On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net>
wrote:

>flobert wrote:
>> On Fri, 19 Aug 2005 20:08:04 -0700, jim beam <nospam@example.net>
>> wrote:
>>
>>
>>>flobert wrote:
>>>
>>>>On Thu, 18 Aug 2005 19:04:43 GMT, "Larry J."
>>>><usenet2@DE.LETE.THISljvideo.com> wrote:
>>>>
>>>>
>>>>
>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said:
>>>>>
>>>>>
>>>>>
>>>>>>On Thu, 18 Aug 2005 10:39:33 -0600, "'Curly Q. Links'"
>>>>>><motsco_@_interbaun.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Drewaffe wrote:
>>>>>>><SNIP> I shift into Neutral and coast downhill
>>>>>>>
>>>>>>>
>>>>>>>>rather than let the engine do it.
>>>>>>>
>>>>>>>----------------------------
>>>>>>>
>>>>>>>It's illegal to shift into neutral when going downhill, in some
>>>>>>>juristictions. It's for a couple of good reasons. Don't do it.
>>>>>>
>>>>>>And prey tell what ARE those reasons.
>>>>>
>>>>>Much of the speed reduction when going downhill is achieved by taking
>>>>>your foot off the gas and letting the engine do the "brake" work. By
>>>>>putting the transmisison in neutral, you have to rely entirely on
>>>>>your braking system, risking rapid overheating of the brakes.
>>>>>Overheated brakes work very poorly, leaving you open to destruction.
>>>>
>>>>
>>>>Whilst yes, that was the case in the 60s, not since the late 70s at
>>>>the latest has this even been an issue. A semi, comming down a
>>>>mountain, yes, a car down a hill, no. Keep with the times, and stop
>>>>with the decades old misinformation please.
>>>
>>>it's not misinformation, it's dead accurate. brakes linings /do/ over
>>>heat, brake lines fail, brake fluids boil, speeds can become excessive,
>>>and you are not in full control of the vehicle in the event you need to
>>>make any evasive manoevers. it's bad for the transmission too. do not
>>>ever coast in neutral down a hill! /EVER/!
>>
>>
>> For this to work as you say, you'd need the following to happen
>> badly ventilated/cooled brakes.
>> constant application of brakes
>> weakened brake lines
>> under-spec brake fluid
>
>1. all brakes heat on application. that's fundamental fact. if you're
>dissipating /all/ your forward energy through the brakes and are not
>using engine braking because you are in neutral, the brakes will heat
>more!!! that's fact!!!

I'm not arguing that the brakes will generate more heat. I did not at
any time say that. however, brake fading is only an issue in modern
brakes if the temperature goes over a certain temperature. The amount
of fade, and the temperature at which it occurs is variable depending
on the brake type/composition. For instance, brakes in a Formula 1 car
INCREASE in braking abaility as they get hotter, until they actually
burn. there is virtually no fade. They get hot, they get better, they
get too hot, they burn, they dissapear, but it takes a GREAT deal of
heat to burn the,.

I saw some test figures from the development of the Lotus Elise some
10 years ago. They tested the vehicle on an extreme downhill section
of the Alps, at racing constions, and found less than 1% fade. Those
are two clear examples that countradict your blanket assertions.
Modern brakes do not decrease in retardation ability in direct
relationship to their temperature, and haven't for many years.

>
>2. you can easily have constant application of brakes. you're never
>going to have road conditions that just happen to suit you!

So, i can't pick when i'm going to coast? My gearbox has a life of its
own?

What it seems you fail to distinguish here is the difference between
coasting on ALL slopes, regardless of grade, and only doing so where
needed. I will give you two examples from here in Georgia - thers a
series of hills on US19 betwen thomaston and zebulan, they're not
steep gradients, and quite long, i will often coast down them. no
brakes needed, except for the occasioanl momentary check-brake as my
speed rises too high (the southmost slope is by the county line, and
often deputies will hide there checking for speeders). The second
example is a hill much further north - Barnes Mill Road, in Marietta
(just off the 120 loop by exit 265 of I75) a much steeper slope, of
about 1 mile in length, where not only do you keep it in gear, but
have to use your brakes over aout 40% of it. Gradent of the second is
about double that of the first. no-one is suggesting its an 'all or
nothing', and i for one certainly haven't. its you that suggesting
that in all situations, in all circumstances, you're risking life and
limb

>
>3. brake lines deteriorate with age! fact.

Certainly, and if a brake line was to go, it'd be more likely under
the greater heat and pressure of a high speed emergency deceleration,
than under a gentle coasting, where the brakes may or may not be used
at all, see above.

>
>4. brake fluid absorbs water from the air. it starts to degrade the
>moment you open the bottle. fact.

I don't know about you, but i would call brake fluid with heavy water
contamination to be 'under spec'


>
>>
>> Any of these would occur in any sudden deceleration from a high speed
>> (such as an emergency stop on the highway) and be in all probablility
>> more fatel then.
>
>that's stupid.

Whats stupid? The forces and energies invloved in any high speed
sudden deceleration are much more severe on a vehicle's braking
system, than, as you're suggesting, lightly riding them for a mile or
two.

>
>>
>> Modern brakes are designed to cope with small aplication loads for
>> longer periods of time. Many car manufacturers do these kinds of
>> manouvers as tests in their brake systems, to prevent precisely this
>> from happening. /whats more, its the very first fade test. Were you
>> then to take the car on a long winding downhill run from the mountains
>> you'd have a lot more heat buildup in your brakes, and a lot greater
>> application of wear, having heaier repeated applications of the
>> brakes, with a lower ventilation speed.
>
>you don't know what you're talking about. any brake fades as a function
>of temperature. temperature is a function of the speed you want to turn
>into kinetic energy. any form of stop start driving, regardless of
>hills, heats brakes. period.

fraid not. go look up some test results, there is no direct
corrolation between fade and temperature on modern brakes. no straight
line graph that starts with retardation ability being at max when the
temperature is some 'cold point' that we should take to be air ambent
temp, with retardation ability dropping in direct response to
temperature increase. There is instead a gradual decrease from the
brak systems optimal temperature (whichis NOT air ambient) to the 'max
operating' and then a more rapid decrease.

>
>>
>> You're also on the assumption tha when coasting, people ride the brake
>> instead. you know, i've never done that. if i coast, i don't then ride
>> the brake, instead i'll make a check application, every so often.
>
>dude, apart from the fact that coasting is illegal, you're also
>indicating you don't have the vehicle under proper control.

I asked a friend (a deputy in the next county) and he's never heard of
any such law here. Another fact in error/

>
>>
>> As for the 'not in full control' argument, again, thats from the 50's
>> and 60's before the advent of the nice modern synchromesh.
>
>eh? what has synchromesh got to do with it? that's utterly irrelevant.

prior to the synchromesh, when changing gear, entering a gear etc. -
it was neccesary to adjust the engine speed to match, to select the
gear, and so on. with a synchromesh, its easy to put the car in any
gear suitable for the speed of the vehicle. That was the basis of the
original 'loss of control' arguments - you had no near-immediate
ability to recouple the engine to the wheels.

>
>> For an
>> avoidance measure, engine power or no will make no difference.
>
>but engine braking does!!! that's why automatics down-shift - for
>engine braking and safety.

how does engine braking work to increase safety?

>
>> For
>> stopping, your braking speed is limitedby the static friction lmiit of
>> the vehicles tyres.
>
>only if the brakes can supply sufficient friction. if they're toast,
>you can have the best tires in the world, but they won't mean a damned
>thing to stop you running into that kid that's just kicked their ball
>into the road.

ok, so let me get your argument straight. engine braking is required
because its unsafe to coast. Its unsafe to coast because everyone that
does so, does so with badly adjusted and maintained brakes, and
insists on riding those brakes to the point of failure whilst
coasting. thus when there is an emergency, the small engine
retardation effect is then VITAL to stop the car.

I did some tests this adrernoon, using two automatic vehicles, using
an old airstrip here. I weighted things in your favour, by using older
vehicles (which would have brakes more liekly to fade, and have worn
brake systems - a 87 caravan, and an 88 civic. one big car, one little
car. Unfortunatly, both are automatics, but on the upside, they have
drum brakes with cable-operated handbrakes.

I used a speed of 50mph, and attempted a stoping manouver with ONLY
engine braking, so as to measure the braking distance, which can then
be compaired to a standaised figure, such as ohh, the UK DOT standard
braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)

the civic with its 4speed autom box, with me manually downshifting
managed to slow to 8mph in 450ft, and wouldn't slow any further. on
the second run, engaging the handbrake at 20mph reduced the vehicle to
8mph in 420ft and to a stop in 460.
The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
stopped in 430ft with the handbrake application. (well, foot activated
parking brake)

by constrast, the UK figures show the braking distance to be a total
of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
pre-planned stop point. so, 125ft is the actual stopping distance. so
its more than 3x as bad. It gets worse though, since the vehicle used
in the uk govt. figures is a 1964 ford Anglia - a car not noted for
its agility, and which had a braking system marginally better than a
foot operated wooden block pressed to each wheel. Modern cars and SUVs
achieve braking distances almost half that. Both vehicles managed a
standard braking distance of around 100ft (repeated many times - both
with and withouth being in gear)

>
>> In fact, you're not having to brake the rotational
>> inertia of the engine and connected gearbox componants, so you're
>> ahead there too.
>
>what planet are you on??? look up engine braking on google. truck
>manufacturers invest millions in engine braking technology because its
>so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.
>
>> The only way i can see the engine being of any
>> benefit is if you ahve to go FASTER, or a 90dergee+ oversteer
>> situation, but in that case, you'd probably want to change from a
>> cruising gear in any case.
>
>eh?

whats 'eh' about it. The only way the addition of engine power can
assist in any incident is if you are in a spin, or in a situation
where you would be required to go faster. In any other case, the car
being in gear would no be of any consequence, or positive benefit.

>
>>
>> Regardless, I'm sure we'll be able to go around in circles like this,
>> each counter-claiming the other. Instead, i'll send an email over to
>> see if Mythbusters will take a look at it.
>
>be my guest. geeze. i can maybe understand ignorance as an excuse if
>the engineering is not understood, but using it as an excuse against the
>law??? buddy, you take the prize!

Ignorance of engineering is, apprantly, your forte. As is indeed
ignorance of the law. If it was so illegal, why did Saab in the 70s
sell vehicles that were despigned to freewheel down hills without
having to take the car out of gear, you only had to pull a lever i
think it was. It was discontinued mainly because most drivers didn't
use it, and felt uncomfortable when they did, mainly due to the
commonly held misconception you share.

This, like any long term myth, is one that clearly won't go away after
having being delt with in common sense. In short, you say that if you
coast down any hill, you must coast down all (can't pick your
situation, as you call it) and you must ride your brakes at al times.
Oh, and you have an old brake system, that's been poorly maintained,
so they would fade to nothing (despite the fact it would fail at the
50mph braking test above, due to the greater heat generation vs
dissipation, on your straight-line temp-retardation graph) and that in
an emergency, a braking system that has no effect on actual
deceleration under proper braking, and which has very poor
deceleration figures when used on its own is not only usefull, but
legally required to be used. Would you care to attempt to refute these
facts, maybe do some measurements of your own with your own vehicles.
Maybe even employ some simple logic.

 

On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net>
wrote:

>flobert wrote:
>> On Fri, 19 Aug 2005 20:08:04 -0700, jim beam <nospam@example.net>
>> wrote:
>>
>>
>>>flobert wrote:
>>>
>>>>On Thu, 18 Aug 2005 19:04:43 GMT, "Larry J."
>>>><usenet2@DE.LETE.THISljvideo.com> wrote:
>>>>
>>>>
>>>>
>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said:
>>>>>
>>>>>
>>>>>
>>>>>>On Thu, 18 Aug 2005 10:39:33 -0600, "'Curly Q. Links'"
>>>>>><motsco_@_interbaun.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Drewaffe wrote:
>>>>>>><SNIP> I shift into Neutral and coast downhill
>>>>>>>
>>>>>>>
>>>>>>>>rather than let the engine do it.
>>>>>>>
>>>>>>>----------------------------
>>>>>>>
>>>>>>>It's illegal to shift into neutral when going downhill, in some
>>>>>>>juristictions. It's for a couple of good reasons. Don't do it.
>>>>>>
>>>>>>And prey tell what ARE those reasons.
>>>>>
>>>>>Much of the speed reduction when going downhill is achieved by taking
>>>>>your foot off the gas and letting the engine do the "brake" work. By
>>>>>putting the transmisison in neutral, you have to rely entirely on
>>>>>your braking system, risking rapid overheating of the brakes.
>>>>>Overheated brakes work very poorly, leaving you open to destruction.
>>>>
>>>>
>>>>Whilst yes, that was the case in the 60s, not since the late 70s at
>>>>the latest has this even been an issue. A semi, comming down a
>>>>mountain, yes, a car down a hill, no. Keep with the times, and stop
>>>>with the decades old misinformation please.
>>>
>>>it's not misinformation, it's dead accurate. brakes linings /do/ over
>>>heat, brake lines fail, brake fluids boil, speeds can become excessive,
>>>and you are not in full control of the vehicle in the event you need to
>>>make any evasive manoevers. it's bad for the transmission too. do not
>>>ever coast in neutral down a hill! /EVER/!
>>
>>
>> For this to work as you say, you'd need the following to happen
>> badly ventilated/cooled brakes.
>> constant application of brakes
>> weakened brake lines
>> under-spec brake fluid
>
>1. all brakes heat on application. that's fundamental fact. if you're
>dissipating /all/ your forward energy through the brakes and are not
>using engine braking because you are in neutral, the brakes will heat
>more!!! that's fact!!!

I'm not arguing that the brakes will generate more heat. I did not at
any time say that. however, brake fading is only an issue in modern
brakes if the temperature goes over a certain temperature. The amount
of fade, and the temperature at which it occurs is variable depending
on the brake type/composition. For instance, brakes in a Formula 1 car
INCREASE in braking abaility as they get hotter, until they actually
burn. there is virtually no fade. They get hot, they get better, they
get too hot, they burn, they dissapear, but it takes a GREAT deal of
heat to burn the,.

I saw some test figures from the development of the Lotus Elise some
10 years ago. They tested the vehicle on an extreme downhill section
of the Alps, at racing constions, and found less than 1% fade. Those
are two clear examples that countradict your blanket assertions.
Modern brakes do not decrease in retardation ability in direct
relationship to their temperature, and haven't for many years.

>
>2. you can easily have constant application of brakes. you're never
>going to have road conditions that just happen to suit you!

So, i can't pick when i'm going to coast? My gearbox has a life of its
own?

What it seems you fail to distinguish here is the difference between
coasting on ALL slopes, regardless of grade, and only doing so where
needed. I will give you two examples from here in Georgia - thers a
series of hills on US19 betwen thomaston and zebulan, they're not
steep gradients, and quite long, i will often coast down them. no
brakes needed, except for the occasioanl momentary check-brake as my
speed rises too high (the southmost slope is by the county line, and
often deputies will hide there checking for speeders). The second
example is a hill much further north - Barnes Mill Road, in Marietta
(just off the 120 loop by exit 265 of I75) a much steeper slope, of
about 1 mile in length, where not only do you keep it in gear, but
have to use your brakes over aout 40% of it. Gradent of the second is
about double that of the first. no-one is suggesting its an 'all or
nothing', and i for one certainly haven't. its you that suggesting
that in all situations, in all circumstances, you're risking life and
limb

>
>3. brake lines deteriorate with age! fact.

Certainly, and if a brake line was to go, it'd be more likely under
the greater heat and pressure of a high speed emergency deceleration,
than under a gentle coasting, where the brakes may or may not be used
at all, see above.

>
>4. brake fluid absorbs water from the air. it starts to degrade the
>moment you open the bottle. fact.

I don't know about you, but i would call brake fluid with heavy water
contamination to be 'under spec'


>
>>
>> Any of these would occur in any sudden deceleration from a high speed
>> (such as an emergency stop on the highway) and be in all probablility
>> more fatel then.
>
>that's stupid.

Whats stupid? The forces and energies invloved in any high speed
sudden deceleration are much more severe on a vehicle's braking
system, than, as you're suggesting, lightly riding them for a mile or
two.

>
>>
>> Modern brakes are designed to cope with small aplication loads for
>> longer periods of time. Many car manufacturers do these kinds of
>> manouvers as tests in their brake systems, to prevent precisely this
>> from happening. /whats more, its the very first fade test. Were you
>> then to take the car on a long winding downhill run from the mountains
>> you'd have a lot more heat buildup in your brakes, and a lot greater
>> application of wear, having heaier repeated applications of the
>> brakes, with a lower ventilation speed.
>
>you don't know what you're talking about. any brake fades as a function
>of temperature. temperature is a function of the speed you want to turn
>into kinetic energy. any form of stop start driving, regardless of
>hills, heats brakes. period.

fraid not. go look up some test results, there is no direct
corrolation between fade and temperature on modern brakes. no straight
line graph that starts with retardation ability being at max when the
temperature is some 'cold point' that we should take to be air ambent
temp, with retardation ability dropping in direct response to
temperature increase. There is instead a gradual decrease from the
brak systems optimal temperature (whichis NOT air ambient) to the 'max
operating' and then a more rapid decrease.

>
>>
>> You're also on the assumption tha when coasting, people ride the brake
>> instead. you know, i've never done that. if i coast, i don't then ride
>> the brake, instead i'll make a check application, every so often.
>
>dude, apart from the fact that coasting is illegal, you're also
>indicating you don't have the vehicle under proper control.

I asked a friend (a deputy in the next county) and he's never heard of
any such law here. Another fact in error/

>
>>
>> As for the 'not in full control' argument, again, thats from the 50's
>> and 60's before the advent of the nice modern synchromesh.
>
>eh? what has synchromesh got to do with it? that's utterly irrelevant.

prior to the synchromesh, when changing gear, entering a gear etc. -
it was neccesary to adjust the engine speed to match, to select the
gear, and so on. with a synchromesh, its easy to put the car in any
gear suitable for the speed of the vehicle. That was the basis of the
original 'loss of control' arguments - you had no near-immediate
ability to recouple the engine to the wheels.

>
>> For an
>> avoidance measure, engine power or no will make no difference.
>
>but engine braking does!!! that's why automatics down-shift - for
>engine braking and safety.

how does engine braking work to increase safety?

>
>> For
>> stopping, your braking speed is limitedby the static friction lmiit of
>> the vehicles tyres.
>
>only if the brakes can supply sufficient friction. if they're toast,
>you can have the best tires in the world, but they won't mean a damned
>thing to stop you running into that kid that's just kicked their ball
>into the road.

ok, so let me get your argument straight. engine braking is required
because its unsafe to coast. Its unsafe to coast because everyone that
does so, does so with badly adjusted and maintained brakes, and
insists on riding those brakes to the point of failure whilst
coasting. thus when there is an emergency, the small engine
retardation effect is then VITAL to stop the car.

I did some tests this adrernoon, using two automatic vehicles, using
an old airstrip here. I weighted things in your favour, by using older
vehicles (which would have brakes more liekly to fade, and have worn
brake systems - a 87 caravan, and an 88 civic. one big car, one little
car. Unfortunatly, both are automatics, but on the upside, they have
drum brakes with cable-operated handbrakes.

I used a speed of 50mph, and attempted a stoping manouver with ONLY
engine braking, so as to measure the braking distance, which can then
be compaired to a standaised figure, such as ohh, the UK DOT standard
braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)

the civic with its 4speed autom box, with me manually downshifting
managed to slow to 8mph in 450ft, and wouldn't slow any further. on
the second run, engaging the handbrake at 20mph reduced the vehicle to
8mph in 420ft and to a stop in 460.
The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
stopped in 430ft with the handbrake application. (well, foot activated
parking brake)

by constrast, the UK figures show the braking distance to be a total
of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
pre-planned stop point. so, 125ft is the actual stopping distance. so
its more than 3x as bad. It gets worse though, since the vehicle used
in the uk govt. figures is a 1964 ford Anglia - a car not noted for
its agility, and which had a braking system marginally better than a
foot operated wooden block pressed to each wheel. Modern cars and SUVs
achieve braking distances almost half that. Both vehicles managed a
standard braking distance of around 100ft (repeated many times - both
with and withouth being in gear)

>
>> In fact, you're not having to brake the rotational
>> inertia of the engine and connected gearbox componants, so you're
>> ahead there too.
>
>what planet are you on??? look up engine braking on google. truck
>manufacturers invest millions in engine braking technology because its
>so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.
>
>> The only way i can see the engine being of any
>> benefit is if you ahve to go FASTER, or a 90dergee+ oversteer
>> situation, but in that case, you'd probably want to change from a
>> cruising gear in any case.
>
>eh?

whats 'eh' about it. The only way the addition of engine power can
assist in any incident is if you are in a spin, or in a situation
where you would be required to go faster. In any other case, the car
being in gear would no be of any consequence, or positive benefit.

>
>>
>> Regardless, I'm sure we'll be able to go around in circles like this,
>> each counter-claiming the other. Instead, i'll send an email over to
>> see if Mythbusters will take a look at it.
>
>be my guest. geeze. i can maybe understand ignorance as an excuse if
>the engineering is not understood, but using it as an excuse against the
>law??? buddy, you take the prize!

Ignorance of engineering is, apprantly, your forte. As is indeed
ignorance of the law. If it was so illegal, why did Saab in the 70s
sell vehicles that were despigned to freewheel down hills without
having to take the car out of gear, you only had to pull a lever i
think it was. It was discontinued mainly because most drivers didn't
use it, and felt uncomfortable when they did, mainly due to the
commonly held misconception you share.

This, like any long term myth, is one that clearly won't go away after
having being delt with in common sense. In short, you say that if you
coast down any hill, you must coast down all (can't pick your
situation, as you call it) and you must ride your brakes at al times.
Oh, and you have an old brake system, that's been poorly maintained,
so they would fade to nothing (despite the fact it would fail at the
50mph braking test above, due to the greater heat generation vs
dissipation, on your straight-line temp-retardation graph) and that in
an emergency, a braking system that has no effect on actual
deceleration under proper braking, and which has very poor
deceleration figures when used on its own is not only usefull, but
legally required to be used. Would you care to attempt to refute these
facts, maybe do some measurements of your own with your own vehicles.
Maybe even employ some simple logic.

 

"jim beam" <nospam@example.net> wrote
> it's not misinformation, it's dead accurate. brakes linings /do/ over
> heat, brake lines fail, brake fluids boil, speeds can become excessive,
> and you are not in full control of the vehicle in the event you need to
> make any evasive manoevers. it's bad for the transmission too. do not
> ever coast in neutral down a hill! /EVER/!

When you admit you have ceased to speed on a regular basis, then you might
be worth listening to when it comes to safety issues.

Quit freaking out over casual coasting. If you must whine, whine out riding
the brakes.

 

"jim beam" <nospam@example.net> wrote
> it's not misinformation, it's dead accurate. brakes linings /do/ over
> heat, brake lines fail, brake fluids boil, speeds can become excessive,
> and you are not in full control of the vehicle in the event you need to
> make any evasive manoevers. it's bad for the transmission too. do not
> ever coast in neutral down a hill! /EVER/!

When you admit you have ceased to speed on a regular basis, then you might
be worth listening to when it comes to safety issues.

Quit freaking out over casual coasting. If you must whine, whine out riding
the brakes.

 

flobert wrote:
> On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net>
> wrote:
>
>
>>flobert wrote:
>>
>>>On Fri, 19 Aug 2005 20:08:04 -0700, jim beam <nospam@example.net>
>>>wrote:
>>>
>>>
>>>
>>>>flobert wrote:
>>>>
>>>>
>>>>>On Thu, 18 Aug 2005 19:04:43 GMT, "Larry J."
>>>>><usenet2@DE.LETE.THISljvideo.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>On Thu, 18 Aug 2005 10:39:33 -0600, "'Curly Q. Links'"
>>>>>>><motsco_@_interbaun.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>Drewaffe wrote:
>>>>>>>><SNIP> I shift into Neutral and coast downhill
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>rather than let the engine do it.
>>>>>>>>
>>>>>>>>----------------------------
>>>>>>>>
>>>>>>>>It's illegal to shift into neutral when going downhill, in some
>>>>>>>>juristictions. It's for a couple of good reasons. Don't do it.
>>>>>>>
>>>>>>>And prey tell what ARE those reasons.
>>>>>>
>>>>>>Much of the speed reduction when going downhill is achieved by taking
>>>>>>your foot off the gas and letting the engine do the "brake" work. By
>>>>>>putting the transmisison in neutral, you have to rely entirely on
>>>>>>your braking system, risking rapid overheating of the brakes.
>>>>>>Overheated brakes work very poorly, leaving you open to destruction.
>>>>>
>>>>>
>>>>>Whilst yes, that was the case in the 60s, not since the late 70s at
>>>>>the latest has this even been an issue. A semi, comming down a
>>>>>mountain, yes, a car down a hill, no. Keep with the times, and stop
>>>>>with the decades old misinformation please.
>>>>
>>>>it's not misinformation, it's dead accurate. brakes linings /do/ over
>>>>heat, brake lines fail, brake fluids boil, speeds can become excessive,
>>>>and you are not in full control of the vehicle in the event you need to
>>>>make any evasive manoevers. it's bad for the transmission too. do not
>>>>ever coast in neutral down a hill! /EVER/!
>>>
>>>
>>>For this to work as you say, you'd need the following to happen
>>>badly ventilated/cooled brakes.
>>>constant application of brakes
>>>weakened brake lines
>>>under-spec brake fluid
>>
>>1. all brakes heat on application. that's fundamental fact. if you're
>>dissipating /all/ your forward energy through the brakes and are not
>>using engine braking because you are in neutral, the brakes will heat
>>more!!! that's fact!!!
>
>
> I'm not arguing that the brakes will generate more heat. I did not at
> any time say that. however, brake fading is only an issue in modern
> brakes if the temperature goes over a certain temperature. The amount
> of fade, and the temperature at which it occurs is variable depending
> on the brake type/composition. For instance, brakes in a Formula 1 car
> INCREASE in braking abaility as they get hotter, until they actually
> burn. there is virtually no fade. They get hot, they get better, they
> get too hot, they burn, they dissapear, but it takes a GREAT deal of
> heat to burn the,.

those are carbon fiber brakes. they're banned for road use and for
motorcycle track use. different materials behave different. the
materials we're discussing here, cast iron brake disks and carbon/aramid
fiber/ceramic/metal pad composites do not exhibit those characteristics.
they progressively fade as temperature rises. certain formulations
used on racing/performance cars fade less at high temperatures, and oem
honda pads are better than many after-market ones, but they all still
fade. citing an illegal unobtainable exotic is clutching at straws.

>
> I saw some test figures from the development of the Lotus Elise some
> 10 years ago. They tested the vehicle on an extreme downhill section
> of the Alps, at racing constions, and found less than 1% fade. Those
> are two clear examples that countradict your blanket assertions.
> Modern brakes do not decrease in retardation ability in direct
> relationship to their temperature, and haven't for many years.

dude, i used to live in san francisco. and i still work there. have
you ever driven down filbert st hill from broadway to lombard, stopping
at every stop sign? using a crappy set of aftermarket brake pads that
fade like mfsob's? i have. don't talk to me about brake fade being a
thing of the past.

>
>
>>2. you can easily have constant application of brakes. you're never
>>going to have road conditions that just happen to suit you!
>
>
> So, i can't pick when i'm going to coast? My gearbox has a life of its
> own?

not legally, no. how many times do you need to be told? if you have an
accident and the cops investigate, they'll throw the book at you.
assuming you don't run into me of course, in which case the cops would
be the least of your concerns.

>
> What it seems you fail to distinguish here is the difference between
> coasting on ALL slopes, regardless of grade, and only doing so where
> needed. I will give you two examples from here in Georgia - thers a
> series of hills on US19 betwen thomaston and zebulan, they're not
> steep gradients, and quite long, i will often coast down them. no
> brakes needed, except for the occasioanl momentary check-brake as my
> speed rises too high (the southmost slope is by the county line, and
> often deputies will hide there checking for speeders). The second
> example is a hill much further north - Barnes Mill Road, in Marietta
> (just off the 120 loop by exit 265 of I75) a much steeper slope, of
> about 1 mile in length, where not only do you keep it in gear, but
> have to use your brakes over aout 40% of it. Gradent of the second is
> about double that of the first. no-one is suggesting its an 'all or
> nothing', and i for one certainly haven't. its you that suggesting
> that in all situations, in all circumstances, you're risking life and
> limb

1. so you waste gas because your fuel injected car /is/ injecting gas
while you're idling not engine braking

2. you don't have the vehicle under full control /and/

3. you're using brakes where you needn't?

wow, how did nasa ever miss the opportunity of hiring you?

>
>
>>3. brake lines deteriorate with age! fact.
>
>
> Certainly, and if a brake line was to go, it'd be more likely under
> the greater heat and pressure of a high speed emergency deceleration,
> than under a gentle coasting, where the brakes may or may not be used
> at all, see above.

but dude, you're using the brakes /more/ when coasting in neutral!!!

>
>
>>4. brake fluid absorbs water from the air. it starts to degrade the
>>moment you open the bottle. fact.
>
>
> I don't know about you, but i would call brake fluid with heavy water
> contamination to be 'under spec'

water absorbtion means lowers boiling point. excess brake use
approaches the boiling point of a contaminated system more quickly!!!

>
>
>
>>>Any of these would occur in any sudden deceleration from a high speed
>>>(such as an emergency stop on the highway) and be in all probablility
>>>more fatel then.
>>
>>that's stupid.
>
>
> Whats stupid? The forces and energies invloved in any high speed
> sudden deceleration are much more severe on a vehicle's braking
> system, than, as you're suggesting, lightly riding them for a mile or
> two.

eh? of course! but the energy you can absorb by braking is a function
of the available temperature delta. if the initial temperature is
already high because you've been riding the brakes, the available delta
is less. it that hard to understand?

>
>
>>>Modern brakes are designed to cope with small aplication loads for
>>>longer periods of time. Many car manufacturers do these kinds of
>>>manouvers as tests in their brake systems, to prevent precisely this
>>>from happening. /whats more, its the very first fade test. Were you
>>>then to take the car on a long winding downhill run from the mountains
>>>you'd have a lot more heat buildup in your brakes, and a lot greater
>>>application of wear, having heaier repeated applications of the
>>>brakes, with a lower ventilation speed.
>>
>>you don't know what you're talking about. any brake fades as a function
>>of temperature. temperature is a function of the speed you want to turn
>>into kinetic energy. any form of stop start driving, regardless of
>>hills, heats brakes. period.
>
>
> fraid not. go look up some test results, there is no direct
> corrolation between fade and temperature on modern brakes.

rubbish.

> no straight
> line graph that starts with retardation ability being at max when the
> temperature is some 'cold point' that we should take to be air ambent
> temp, with retardation ability dropping in direct response to
> temperature increase.

dude, you're turning speed into heat. if the brakes fade more as the
temperature rises, and they do, you want the initial temperature to me
minimized.

> There is instead a gradual decrease from the
> brak systems optimal temperature (whichis NOT air ambient) to the 'max
> operating' and then a more rapid decrease.

so what is "optimal" for a normal car braking system??? and there's no
physical way brake temperature can decrease if you're dumping kinetic
energy into them.

>
>
>>>You're also on the assumption tha when coasting, people ride the brake
>>>instead. you know, i've never done that. if i coast, i don't then ride
>>>the brake, instead i'll make a check application, every so often.
>>
>>dude, apart from the fact that coasting is illegal, you're also
>>indicating you don't have the vehicle under proper control.
>
>
> I asked a friend (a deputy in the next county) and he's never heard of
> any such law here. Another fact in error/

california vehicle code #21710.

"Coasting Prohibited. The driver of a motor vehicle when traveling on
down grade upon any highway shall not coast with the gears of such
vehicle in neutral."


>
>
>>>As for the 'not in full control' argument, again, thats from the 50's
>>>and 60's before the advent of the nice modern synchromesh.
>>
>>eh? what has synchromesh got to do with it? that's utterly irrelevant.
>
>
> prior to the synchromesh, when changing gear, entering a gear etc. -
> it was neccesary to adjust the engine speed to match, to select the
> gear, and so on. with a synchromesh, its easy to put the car in any
> gear suitable for the speed of the vehicle. That was the basis of the
> original 'loss of control' arguments - you had no near-immediate
> ability to recouple the engine to the wheels.

rubbish. if you can't get the vehicle into gear, whether it's automatic
or stick, synchro or not [i've driven non-synchro transmissions and
there's no reason you can't shift if you double-clutch] then either
you're not competent or the vehicle is defective and shouldn't be on the
road. again, synchro is irrelevant.

>
>
>>>For an
>>>avoidance measure, engine power or no will make no difference.
>>
>>but engine braking does!!! that's why automatics down-shift - for
>>engine braking and safety.
>
>
> how does engine braking work to increase safety?

because, as mentioned so many times before, it takes a substantial load
off the brakes!!! it also allows you to instantly re-power the vehicle
if required.

>
>
>>>For
>>>stopping, your braking speed is limitedby the static friction lmiit of
>>>the vehicles tyres.
>>
>>only if the brakes can supply sufficient friction. if they're toast,
>>you can have the best tires in the world, but they won't mean a damned
>>thing to stop you running into that kid that's just kicked their ball
>>into the road.
>
>
> ok, so let me get your argument straight. engine braking is required
> because its unsafe to coast. Its unsafe to coast because everyone that
> does so, does so with badly adjusted and maintained brakes, and
> insists on riding those brakes to the point of failure whilst
> coasting. thus when there is an emergency, the small engine
> retardation effect is then VITAL to stop the car.

no, it's necessary to keep the brakes cool for maximum stopping power.
remember the temperature delta thing???

>
> I did some tests this adrernoon, using two automatic vehicles, using
> an old airstrip here. I weighted things in your favour, by using older
> vehicles (which would have brakes more liekly to fade, and have worn
> brake systems - a 87 caravan, and an 88 civic. one big car, one little
> car. Unfortunatly, both are automatics, but on the upside, they have
> drum brakes with cable-operated handbrakes.
>
> I used a speed of 50mph, and attempted a stoping manouver with ONLY
> engine braking, so as to measure the braking distance, which can then
> be compaired to a standaised figure, such as ohh, the UK DOT standard
> braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)
>
> the civic with its 4speed autom box, with me manually downshifting
> managed to slow to 8mph in 450ft, and wouldn't slow any further. on
> the second run, engaging the handbrake at 20mph reduced the vehicle to
> 8mph in 420ft and to a stop in 460.
> The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
> stopped in 430ft with the handbrake application. (well, foot activated
> parking brake)
>
> by constrast, the UK figures show the braking distance to be a total
> of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
> pre-planned stop point. so, 125ft is the actual stopping distance. so
> its more than 3x as bad. It gets worse though, since the vehicle used
> in the uk govt. figures is a 1964 ford Anglia - a car not noted for
> its agility, and which had a braking system marginally better than a
> foot operated wooden block pressed to each wheel. Modern cars and SUVs
> achieve braking distances almost half that. Both vehicles managed a
> standard braking distance of around 100ft (repeated many times - both
> with and withouth being in gear)

dude, the engine does not /stop/ the car [unless you turn off the
ignition]. but it does offer braking in proportion to engine speed
[which is why you downshift when engine braking] and yet again, this
reduces the thermal load on the brakes. that's why cars with automatic
transmissions, like honda, detect when the car is braking and down-shift
to increase engine braking. i guess you'd never notice that if you
habitually coast in neutral, but it's fact nevertheless.

>
>
>>>In fact, you're not having to brake the rotational
>>>inertia of the engine and connected gearbox componants, so you're
>>>ahead there too.
>>
>>what planet are you on??? look up engine braking on google. truck
>>manufacturers invest millions in engine braking technology because its
>>so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.
>>
>>
>>>The only way i can see the engine being of any
>>>benefit is if you ahve to go FASTER, or a 90dergee+ oversteer
>>>situation, but in that case, you'd probably want to change from a
>>>cruising gear in any case.
>>
>>eh?
>
>
> whats 'eh' about it. The only way the addition of engine power can
> assist in any incident is if you are in a spin, or in a situation
> where you would be required to go faster. In any other case, the car
> being in gear would no be of any consequence, or positive benefit.

so these situations never occur? you should know that it does rain
occasionally...

>
>
>>>Regardless, I'm sure we'll be able to go around in circles like this,
>>>each counter-claiming the other. Instead, i'll send an email over to
>>>see if Mythbusters will take a look at it.
>>
>>be my guest. geeze. i can maybe understand ignorance as an excuse if
>>the engineering is not understood, but using it as an excuse against the
>>law??? buddy, you take the prize!
>
>
> Ignorance of engineering is, apprantly, your forte. As is indeed
> ignorance of the law. If it was so illegal, why did Saab in the 70s
> sell vehicles that were despigned to freewheel down hills without
> having to take the car out of gear, you only had to pull a lever i
> think it was. It was discontinued mainly because most drivers didn't
> use it, and felt uncomfortable when they did, mainly due to the
> commonly held misconception you share.

well, funky cv transmissioned daf's & volvos had a button that
/increased/ engine braking for downhill situations. one of these
situations does not compute.

>
> This, like any long term myth, is one that clearly won't go away after
> having being delt with in common sense. In short, you say that if you
> coast down any hill, you must coast down all (can't pick your
> situation, as you call it) and you must ride your brakes at al times.

you're the guy riding brakes. i use the engine.

> Oh, and you have an old brake system, that's been poorly maintained,
> so they would fade to nothing (despite the fact it would fail at the
> 50mph braking test above, due to the greater heat generation vs
> dissipation, on your straight-line temp-retardation graph) and that in
> an emergency, a braking system that has no effect on actual
> deceleration under proper braking, and which has very poor
> deceleration figures when used on its own is not only usefull, but
> legally required to be used. Would you care to attempt to refute these
> facts, maybe do some measurements of your own with your own vehicles.
> Maybe even employ some simple logic.

no. you're using twisted logic to put utterly incorrect words in my
mouth. the physics are very simple: a brake turns kinetic energy into
heat. as the temperature rises, the ability to continue turning k.e.
into heat falls. let me know if you can grasp that concept, then we can
continue this discussion.

 

flobert wrote:
> On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net>
> wrote:
>
>
>>flobert wrote:
>>
>>>On Fri, 19 Aug 2005 20:08:04 -0700, jim beam <nospam@example.net>
>>>wrote:
>>>
>>>
>>>
>>>>flobert wrote:
>>>>
>>>>
>>>>>On Thu, 18 Aug 2005 19:04:43 GMT, "Larry J."
>>>>><usenet2@DE.LETE.THISljvideo.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>On Thu, 18 Aug 2005 10:39:33 -0600, "'Curly Q. Links'"
>>>>>>><motsco_@_interbaun.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>Drewaffe wrote:
>>>>>>>><SNIP> I shift into Neutral and coast downhill
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>rather than let the engine do it.
>>>>>>>>
>>>>>>>>----------------------------
>>>>>>>>
>>>>>>>>It's illegal to shift into neutral when going downhill, in some
>>>>>>>>juristictions. It's for a couple of good reasons. Don't do it.
>>>>>>>
>>>>>>>And prey tell what ARE those reasons.
>>>>>>
>>>>>>Much of the speed reduction when going downhill is achieved by taking
>>>>>>your foot off the gas and letting the engine do the "brake" work. By
>>>>>>putting the transmisison in neutral, you have to rely entirely on
>>>>>>your braking system, risking rapid overheating of the brakes.
>>>>>>Overheated brakes work very poorly, leaving you open to destruction.
>>>>>
>>>>>
>>>>>Whilst yes, that was the case in the 60s, not since the late 70s at
>>>>>the latest has this even been an issue. A semi, comming down a
>>>>>mountain, yes, a car down a hill, no. Keep with the times, and stop
>>>>>with the decades old misinformation please.
>>>>
>>>>it's not misinformation, it's dead accurate. brakes linings /do/ over
>>>>heat, brake lines fail, brake fluids boil, speeds can become excessive,
>>>>and you are not in full control of the vehicle in the event you need to
>>>>make any evasive manoevers. it's bad for the transmission too. do not
>>>>ever coast in neutral down a hill! /EVER/!
>>>
>>>
>>>For this to work as you say, you'd need the following to happen
>>>badly ventilated/cooled brakes.
>>>constant application of brakes
>>>weakened brake lines
>>>under-spec brake fluid
>>
>>1. all brakes heat on application. that's fundamental fact. if you're
>>dissipating /all/ your forward energy through the brakes and are not
>>using engine braking because you are in neutral, the brakes will heat
>>more!!! that's fact!!!
>
>
> I'm not arguing that the brakes will generate more heat. I did not at
> any time say that. however, brake fading is only an issue in modern
> brakes if the temperature goes over a certain temperature. The amount
> of fade, and the temperature at which it occurs is variable depending
> on the brake type/composition. For instance, brakes in a Formula 1 car
> INCREASE in braking abaility as they get hotter, until they actually
> burn. there is virtually no fade. They get hot, they get better, they
> get too hot, they burn, they dissapear, but it takes a GREAT deal of
> heat to burn the,.

those are carbon fiber brakes. they're banned for road use and for
motorcycle track use. different materials behave different. the
materials we're discussing here, cast iron brake disks and carbon/aramid
fiber/ceramic/metal pad composites do not exhibit those characteristics.
they progressively fade as temperature rises. certain formulations
used on racing/performance cars fade less at high temperatures, and oem
honda pads are better than many after-market ones, but they all still
fade. citing an illegal unobtainable exotic is clutching at straws.

>
> I saw some test figures from the development of the Lotus Elise some
> 10 years ago. They tested the vehicle on an extreme downhill section
> of the Alps, at racing constions, and found less than 1% fade. Those
> are two clear examples that countradict your blanket assertions.
> Modern brakes do not decrease in retardation ability in direct
> relationship to their temperature, and haven't for many years.

dude, i used to live in san francisco. and i still work there. have
you ever driven down filbert st hill from broadway to lombard, stopping
at every stop sign? using a crappy set of aftermarket brake pads that
fade like mfsob's? i have. don't talk to me about brake fade being a
thing of the past.

>
>
>>2. you can easily have constant application of brakes. you're never
>>going to have road conditions that just happen to suit you!
>
>
> So, i can't pick when i'm going to coast? My gearbox has a life of its
> own?

not legally, no. how many times do you need to be told? if you have an
accident and the cops investigate, they'll throw the book at you.
assuming you don't run into me of course, in which case the cops would
be the least of your concerns.

>
> What it seems you fail to distinguish here is the difference between
> coasting on ALL slopes, regardless of grade, and only doing so where
> needed. I will give you two examples from here in Georgia - thers a
> series of hills on US19 betwen thomaston and zebulan, they're not
> steep gradients, and quite long, i will often coast down them. no
> brakes needed, except for the occasioanl momentary check-brake as my
> speed rises too high (the southmost slope is by the county line, and
> often deputies will hide there checking for speeders). The second
> example is a hill much further north - Barnes Mill Road, in Marietta
> (just off the 120 loop by exit 265 of I75) a much steeper slope, of
> about 1 mile in length, where not only do you keep it in gear, but
> have to use your brakes over aout 40% of it. Gradent of the second is
> about double that of the first. no-one is suggesting its an 'all or
> nothing', and i for one certainly haven't. its you that suggesting
> that in all situations, in all circumstances, you're risking life and
> limb

1. so you waste gas because your fuel injected car /is/ injecting gas
while you're idling not engine braking

2. you don't have the vehicle under full control /and/

3. you're using brakes where you needn't?

wow, how did nasa ever miss the opportunity of hiring you?

>
>
>>3. brake lines deteriorate with age! fact.
>
>
> Certainly, and if a brake line was to go, it'd be more likely under
> the greater heat and pressure of a high speed emergency deceleration,
> than under a gentle coasting, where the brakes may or may not be used
> at all, see above.

but dude, you're using the brakes /more/ when coasting in neutral!!!

>
>
>>4. brake fluid absorbs water from the air. it starts to degrade the
>>moment you open the bottle. fact.
>
>
> I don't know about you, but i would call brake fluid with heavy water
> contamination to be 'under spec'

water absorbtion means lowers boiling point. excess brake use
approaches the boiling point of a contaminated system more quickly!!!

>
>
>
>>>Any of these would occur in any sudden deceleration from a high speed
>>>(such as an emergency stop on the highway) and be in all probablility
>>>more fatel then.
>>
>>that's stupid.
>
>
> Whats stupid? The forces and energies invloved in any high speed
> sudden deceleration are much more severe on a vehicle's braking
> system, than, as you're suggesting, lightly riding them for a mile or
> two.

eh? of course! but the energy you can absorb by braking is a function
of the available temperature delta. if the initial temperature is
already high because you've been riding the brakes, the available delta
is less. it that hard to understand?

>
>
>>>Modern brakes are designed to cope with small aplication loads for
>>>longer periods of time. Many car manufacturers do these kinds of
>>>manouvers as tests in their brake systems, to prevent precisely this
>>>from happening. /whats more, its the very first fade test. Were you
>>>then to take the car on a long winding downhill run from the mountains
>>>you'd have a lot more heat buildup in your brakes, and a lot greater
>>>application of wear, having heaier repeated applications of the
>>>brakes, with a lower ventilation speed.
>>
>>you don't know what you're talking about. any brake fades as a function
>>of temperature. temperature is a function of the speed you want to turn
>>into kinetic energy. any form of stop start driving, regardless of
>>hills, heats brakes. period.
>
>
> fraid not. go look up some test results, there is no direct
> corrolation between fade and temperature on modern brakes.

rubbish.

> no straight
> line graph that starts with retardation ability being at max when the
> temperature is some 'cold point' that we should take to be air ambent
> temp, with retardation ability dropping in direct response to
> temperature increase.

dude, you're turning speed into heat. if the brakes fade more as the
temperature rises, and they do, you want the initial temperature to me
minimized.

> There is instead a gradual decrease from the
> brak systems optimal temperature (whichis NOT air ambient) to the 'max
> operating' and then a more rapid decrease.

so what is "optimal" for a normal car braking system??? and there's no
physical way brake temperature can decrease if you're dumping kinetic
energy into them.

>
>
>>>You're also on the assumption tha when coasting, people ride the brake
>>>instead. you know, i've never done that. if i coast, i don't then ride
>>>the brake, instead i'll make a check application, every so often.
>>
>>dude, apart from the fact that coasting is illegal, you're also
>>indicating you don't have the vehicle under proper control.
>
>
> I asked a friend (a deputy in the next county) and he's never heard of
> any such law here. Another fact in error/

california vehicle code #21710.

"Coasting Prohibited. The driver of a motor vehicle when traveling on
down grade upon any highway shall not coast with the gears of such
vehicle in neutral."


>
>
>>>As for the 'not in full control' argument, again, thats from the 50's
>>>and 60's before the advent of the nice modern synchromesh.
>>
>>eh? what has synchromesh got to do with it? that's utterly irrelevant.
>
>
> prior to the synchromesh, when changing gear, entering a gear etc. -
> it was neccesary to adjust the engine speed to match, to select the
> gear, and so on. with a synchromesh, its easy to put the car in any
> gear suitable for the speed of the vehicle. That was the basis of the
> original 'loss of control' arguments - you had no near-immediate
> ability to recouple the engine to the wheels.

rubbish. if you can't get the vehicle into gear, whether it's automatic
or stick, synchro or not [i've driven non-synchro transmissions and
there's no reason you can't shift if you double-clutch] then either
you're not competent or the vehicle is defective and shouldn't be on the
road. again, synchro is irrelevant.

>
>
>>>For an
>>>avoidance measure, engine power or no will make no difference.
>>
>>but engine braking does!!! that's why automatics down-shift - for
>>engine braking and safety.
>
>
> how does engine braking work to increase safety?

because, as mentioned so many times before, it takes a substantial load
off the brakes!!! it also allows you to instantly re-power the vehicle
if required.

>
>
>>>For
>>>stopping, your braking speed is limitedby the static friction lmiit of
>>>the vehicles tyres.
>>
>>only if the brakes can supply sufficient friction. if they're toast,
>>you can have the best tires in the world, but they won't mean a damned
>>thing to stop you running into that kid that's just kicked their ball
>>into the road.
>
>
> ok, so let me get your argument straight. engine braking is required
> because its unsafe to coast. Its unsafe to coast because everyone that
> does so, does so with badly adjusted and maintained brakes, and
> insists on riding those brakes to the point of failure whilst
> coasting. thus when there is an emergency, the small engine
> retardation effect is then VITAL to stop the car.

no, it's necessary to keep the brakes cool for maximum stopping power.
remember the temperature delta thing???

>
> I did some tests this adrernoon, using two automatic vehicles, using
> an old airstrip here. I weighted things in your favour, by using older
> vehicles (which would have brakes more liekly to fade, and have worn
> brake systems - a 87 caravan, and an 88 civic. one big car, one little
> car. Unfortunatly, both are automatics, but on the upside, they have
> drum brakes with cable-operated handbrakes.
>
> I used a speed of 50mph, and attempted a stoping manouver with ONLY
> engine braking, so as to measure the braking distance, which can then
> be compaired to a standaised figure, such as ohh, the UK DOT standard
> braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)
>
> the civic with its 4speed autom box, with me manually downshifting
> managed to slow to 8mph in 450ft, and wouldn't slow any further. on
> the second run, engaging the handbrake at 20mph reduced the vehicle to
> 8mph in 420ft and to a stop in 460.
> The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
> stopped in 430ft with the handbrake application. (well, foot activated
> parking brake)
>
> by constrast, the UK figures show the braking distance to be a total
> of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
> pre-planned stop point. so, 125ft is the actual stopping distance. so
> its more than 3x as bad. It gets worse though, since the vehicle used
> in the uk govt. figures is a 1964 ford Anglia - a car not noted for
> its agility, and which had a braking system marginally better than a
> foot operated wooden block pressed to each wheel. Modern cars and SUVs
> achieve braking distances almost half that. Both vehicles managed a
> standard braking distance of around 100ft (repeated many times - both
> with and withouth being in gear)

dude, the engine does not /stop/ the car [unless you turn off the
ignition]. but it does offer braking in proportion to engine speed
[which is why you downshift when engine braking] and yet again, this
reduces the thermal load on the brakes. that's why cars with automatic
transmissions, like honda, detect when the car is braking and down-shift
to increase engine braking. i guess you'd never notice that if you
habitually coast in neutral, but it's fact nevertheless.

>
>
>>>In fact, you're not having to brake the rotational
>>>inertia of the engine and connected gearbox componants, so you're
>>>ahead there too.
>>
>>what planet are you on??? look up engine braking on google. truck
>>manufacturers invest millions in engine braking technology because its
>>so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.
>>
>>
>>>The only way i can see the engine being of any
>>>benefit is if you ahve to go FASTER, or a 90dergee+ oversteer
>>>situation, but in that case, you'd probably want to change from a
>>>cruising gear in any case.
>>
>>eh?
>
>
> whats 'eh' about it. The only way the addition of engine power can
> assist in any incident is if you are in a spin, or in a situation
> where you would be required to go faster. In any other case, the car
> being in gear would no be of any consequence, or positive benefit.

so these situations never occur? you should know that it does rain
occasionally...

>
>
>>>Regardless, I'm sure we'll be able to go around in circles like this,
>>>each counter-claiming the other. Instead, i'll send an email over to
>>>see if Mythbusters will take a look at it.
>>
>>be my guest. geeze. i can maybe understand ignorance as an excuse if
>>the engineering is not understood, but using it as an excuse against the
>>law??? buddy, you take the prize!
>
>
> Ignorance of engineering is, apprantly, your forte. As is indeed
> ignorance of the law. If it was so illegal, why did Saab in the 70s
> sell vehicles that were despigned to freewheel down hills without
> having to take the car out of gear, you only had to pull a lever i
> think it was. It was discontinued mainly because most drivers didn't
> use it, and felt uncomfortable when they did, mainly due to the
> commonly held misconception you share.

well, funky cv transmissioned daf's & volvos had a button that
/increased/ engine braking for downhill situations. one of these
situations does not compute.

>
> This, like any long term myth, is one that clearly won't go away after
> having being delt with in common sense. In short, you say that if you
> coast down any hill, you must coast down all (can't pick your
> situation, as you call it) and you must ride your brakes at al times.

you're the guy riding brakes. i use the engine.

> Oh, and you have an old brake system, that's been poorly maintained,
> so they would fade to nothing (despite the fact it would fail at the
> 50mph braking test above, due to the greater heat generation vs
> dissipation, on your straight-line temp-retardation graph) and that in
> an emergency, a braking system that has no effect on actual
> deceleration under proper braking, and which has very poor
> deceleration figures when used on its own is not only usefull, but
> legally required to be used. Would you care to attempt to refute these
> facts, maybe do some measurements of your own with your own vehicles.
> Maybe even employ some simple logic.

no. you're using twisted logic to put utterly incorrect words in my
mouth. the physics are very simple: a brake turns kinetic energy into
heat. as the temperature rises, the ability to continue turning k.e.
into heat falls. let me know if you can grasp that concept, then we can
continue this discussion.

 

On Sun, 21 Aug 2005 19:24:36 -0700, jim beam <nospam@example.net>
wrote:

>flobert wrote:
>> On Sat, 20 Aug 2005 12:34:13 -0700, jim beam <nospam@example.net>
>> wrote:
>>
>>
>>>flobert wrote:
>>>
>>>>On Fri, 19 Aug 2005 20:08:04 -0700, jim beam <nospam@example.net>
>>>>wrote:
>>>>
>>>>
>>>>
>>>>>flobert wrote:
>>>>>
>>>>>
>>>>>>On Thu, 18 Aug 2005 19:04:43 GMT, "Larry J."
>>>>>><usenet2@DE.LETE.THISljvideo.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Waiving the right to remain silent, flobert <nomail@here.NOT> said:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>On Thu, 18 Aug 2005 10:39:33 -0600, "'Curly Q. Links'"
>>>>>>>><motsco_@_interbaun.com> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>Drewaffe wrote:
>>>>>>>>><SNIP> I shift into Neutral and coast downhill
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>rather than let the engine do it.
>>>>>>>>>
>>>>>>>>>----------------------------
>>>>>>>>>
>>>>>>>>>It's illegal to shift into neutral when going downhill, in some
>>>>>>>>>juristictions. It's for a couple of good reasons. Don't do it.
>>>>>>>>
>>>>>>>>And prey tell what ARE those reasons.
>>>>>>>
>>>>>>>Much of the speed reduction when going downhill is achieved by taking
>>>>>>>your foot off the gas and letting the engine do the "brake" work. By
>>>>>>>putting the transmisison in neutral, you have to rely entirely on
>>>>>>>your braking system, risking rapid overheating of the brakes.
>>>>>>>Overheated brakes work very poorly, leaving you open to destruction.
>>>>>>
>>>>>>
>>>>>>Whilst yes, that was the case in the 60s, not since the late 70s at
>>>>>>the latest has this even been an issue. A semi, comming down a
>>>>>>mountain, yes, a car down a hill, no. Keep with the times, and stop
>>>>>>with the decades old misinformation please.
>>>>>
>>>>>it's not misinformation, it's dead accurate. brakes linings /do/ over
>>>>>heat, brake lines fail, brake fluids boil, speeds can become excessive,
>>>>>and you are not in full control of the vehicle in the event you need to
>>>>>make any evasive manoevers. it's bad for the transmission too. do not
>>>>>ever coast in neutral down a hill! /EVER/!
>>>>
>>>>
>>>>For this to work as you say, you'd need the following to happen
>>>>badly ventilated/cooled brakes.
>>>>constant application of brakes
>>>>weakened brake lines
>>>>under-spec brake fluid
>>>
>>>1. all brakes heat on application. that's fundamental fact. if you're
>>>dissipating /all/ your forward energy through the brakes and are not
>>>using engine braking because you are in neutral, the brakes will heat
>>>more!!! that's fact!!!
>>
>>
>> I'm not arguing that the brakes will generate more heat. I did not at
>> any time say that. however, brake fading is only an issue in modern
>> brakes if the temperature goes over a certain temperature. The amount
>> of fade, and the temperature at which it occurs is variable depending
>> on the brake type/composition. For instance, brakes in a Formula 1 car
>> INCREASE in braking abaility as they get hotter, until they actually
>> burn. there is virtually no fade. They get hot, they get better, they
>> get too hot, they burn, they dissapear, but it takes a GREAT deal of
>> heat to burn the,.
>
>those are carbon fiber brakes. they're banned for road use and for
>motorcycle track use. different materials behave different. the
>materials we're discussing here, cast iron brake disks and carbon/aramid
>fiber/ceramic/metal pad composites do not exhibit those characteristics.
> they progressively fade as temperature rises. certain formulations
>used on racing/performance cars fade less at high temperatures, and oem
>honda pads are better than many after-market ones, but they all still
>fade. citing an illegal unobtainable exotic is clutching at straws.

One of those was an 'exotic', but the brakes on an elise is fully road
legal - hell, they were designed and developed in the US, in
California actually - I'll dig out the manufacturers name if you want.
I could go and retrofit a set onto my civic or caravan any time I
wanted.

I'd love if you could cite me a make, and manufacturer of a brake
system that had its optimal braking temperature at room temp. Any type
of vehicle will do, as long as its a powered braking system (no
bicycles)

>
>>
>> I saw some test figures from the development of the Lotus Elise some
>> 10 years ago. They tested the vehicle on an extreme downhill section
>> of the Alps, at racing constions, and found less than 1% fade. Those
>> are two clear examples that countradict your blanket assertions.
>> Modern brakes do not decrease in retardation ability in direct
>> relationship to their temperature, and haven't for many years.
>
>dude, i used to live in san francisco. and i still work there. have
>you ever driven down filbert st hill from broadway to lombard, stopping
>at every stop sign? using a crappy set of aftermarket brake pads that
>fade like mfsob's? i have. don't talk to me about brake fade being a
>thing of the past.

Its been about 5 years since i was in san fransisco last (i used to
work on contract for a company, having to drive to, from, around SF
all day long, as well as oakland, sausalito, and yerba buena/treasure
island. i think i only drove over the hill once, usually i take the
tunnel, california street was it? all i remember is driving from the
bay bridge to the GG bridge, i drove past the strip clubs, througha
tunnel, and then joined up with lombard about 3 streets over. First
time i ever drove in America, back then, and the first time i'd ever
driven an automatic on the roads.

From what i remmeber, though, the hills weren't that bad. I id much
heavier testing and laoding of my brakes, i had no fade problems. It
sounds like you need to take better care of your brake system. Use
adequately rated parts, not any old crap you can find.

>
>>
>>
>>>2. you can easily have constant application of brakes. you're never
>>>going to have road conditions that just happen to suit you!
>>
>>
>> So, i can't pick when i'm going to coast? My gearbox has a life of its
>> own?
>
>not legally, no. how many times do you need to be told? if you have an
>accident and the cops investigate, they'll throw the book at you.
>assuming you don't run into me of course, in which case the cops would
>be the least of your concerns.
>
You ahve strange definitions of whats legal and whats not. You believe
that if its illegal in californai, it is everywhere. Its not, as far
as i, and the law enforcment personnel i have questioned, illegal
here, where i am, therefore they would NOT throw the book at me. nor
was it, or is it illegal in the UK - its not reccomended there, but
then neither is crossing your arms on the wheel - the action is not
'citeable'. No action can be taken. In other words, it is legal. Do it
during your driving test, and you will get a minor error, not even an
immediate failing error.

>>
>> What it seems you fail to distinguish here is the difference between
>> coasting on ALL slopes, regardless of grade, and only doing so where
>> needed. I will give you two examples from here in Georgia - thers a
>> series of hills on US19 betwen thomaston and zebulan, they're not
>> steep gradients, and quite long, i will often coast down them. no
>> brakes needed, except for the occasioanl momentary check-brake as my
>> speed rises too high (the southmost slope is by the county line, and
>> often deputies will hide there checking for speeders). The second
>> example is a hill much further north - Barnes Mill Road, in Marietta
>> (just off the 120 loop by exit 265 of I75) a much steeper slope, of
>> about 1 mile in length, where not only do you keep it in gear, but
>> have to use your brakes over aout 40% of it. Gradent of the second is
>> about double that of the first. no-one is suggesting its an 'all or
>> nothing', and i for one certainly haven't. its you that suggesting
>> that in all situations, in all circumstances, you're risking life and
>> limb
>
>1. so you waste gas because your fuel injected car /is/ injecting gas
>while you're idling not engine braking

but i then save it due to the increased momentum when i come to the
next incline - i need to accelerate later. See later for actual
figures.

>
>2. you don't have the vehicle under full control /and/

still not sold me on this 'full control' thing. I've given two
situations, the ONLY two me and the deputy mentioned further down
could think of.

>
>3. you're using brakes where you needn't?

when am i doing that. repeatedly told you, i don't ride the brakes as
part of coasting. I allow the vehicles momentum to increase - thats
half the point. whats the point of concerving the energy of memntum by
not dumping it in the engine, if you're gong to dump it into the
brakes instead?

>
>wow, how did nasa ever miss the opportunity of hiring you?

by me not having applied. Friends already work there, and i've heard
too many bad stories about what moral,a nd the structure and work
situation is like.

>
>>
>>
>>>3. brake lines deteriorate with age! fact.
>>
>>
>> Certainly, and if a brake line was to go, it'd be more likely under
>> the greater heat and pressure of a high speed emergency deceleration,
>> than under a gentle coasting, where the brakes may or may not be used
>> at all, see above.
>
>but dude, you're using the brakes /more/ when coasting in neutral!!!

not really. depends on the hill, the situation, my speed, the speed of
the vehicles around me, and a few other facts under my control. As i
noted previously, on the hills i coasted down (LEGALLY) yesterday, the
brakes were not used at all, and the engine was not put back into gear
until a mile after the last hill, when my speed 'boost' from coasting
had diminished.

>
>>
>>
>>>4. brake fluid absorbs water from the air. it starts to degrade the
>>>moment you open the bottle. fact.
>>
>>
>> I don't know about you, but i would call brake fluid with heavy water
>> contamination to be 'under spec'
>
>water absorbtion means lowers boiling point. excess brake use
>approaches the boiling point of a contaminated system more quickly!!!

yes, and a contaminated system is one which has obviously not been
taken care of. Such fluid would boil, and thus make the car fail under
any severe braking condition. It is thus underspecification, and
dangerous. Any brake fluid this highly contaminated with water should
already ahve been changed.

>
>>
>>
>>
>>>>Any of these would occur in any sudden deceleration from a high speed
>>>>(such as an emergency stop on the highway) and be in all probablility
>>>>more fatel then.
>>>
>>>that's stupid.
>>
>>
>> Whats stupid? The forces and energies invloved in any high speed
>> sudden deceleration are much more severe on a vehicle's braking
>> system, than, as you're suggesting, lightly riding them for a mile or
>> two.
>
>eh? of course! but the energy you can absorb by braking is a function
>of the available temperature delta. if the initial temperature is
>already high because you've been riding the brakes, the available delta
>is less. it that hard to understand?

again, you have this assumption, this ERONOIUS assumption, that
1) you are not using the engine to check the speed thus
2) you MUST be using the brakes to perform the same action.

the problem, that you seem to have trouble accepting is that *shock
horror* 2 does not follow from 1. performing action number 1 does NOT
require action number 2 to be followed. Instead of riding my brakes,
checking my speed, I LET MY SPEED INCREASE. the amount is usually
5-9mph, but it is momentum which keeps me going on the flat at a speed
and for a distance that would require me to re-engage the
transmission, and power my engine, meaning it runs on fuel, a time
earlier. can i quantify those fuel consumptiopn figures, no, i can't.

Hows about this way. on those same hills on US19, that i have
previously described, there is a small hill in between two of the
largest. if i go down that hill, in gear, at a starting speed of
55mph, i have to use about 40% throttle half way up that minor hill in
between, in order to stay above 45mph. If I coast down the first hill,
in neutral, at a starting speed of 55mph, i am up and over the small
hill, and 20% or so up the next big hlil before my speed drops to
45mph.Which uses more fuel? 90 seconds at idle, or 30 seconds at 40%
throttle.

>
>>
>>
>>>>Modern brakes are designed to cope with small aplication loads for
>>>>longer periods of time. Many car manufacturers do these kinds of
>>>>manouvers as tests in their brake systems, to prevent precisely this
>>>>from happening. /whats more, its the very first fade test. Were you
>>>>then to take the car on a long winding downhill run from the mountains
>>>>you'd have a lot more heat buildup in your brakes, and a lot greater
>>>>application of wear, having heaier repeated applications of the
>>>>brakes, with a lower ventilation speed.
>>>
>>>you don't know what you're talking about. any brake fades as a function
>>>of temperature. temperature is a function of the speed you want to turn
>>>into kinetic energy. any form of stop start driving, regardless of
>>>hills, heats brakes. period.
>>
>>
>> fraid not. go look up some test results, there is no direct
>> corrolation between fade and temperature on modern brakes.
>
>rubbish.

of cours,e you say its rubbish, so it must be so. no proof, no
research, one single word. modern brakes are not as simple nowadays as
the brake systems of the 60s and earlier. you do know what 'direct
corrolation' means, don't you? it means there is a very simple,
linearr (no quadratics, or logarythmic functions) equation, of the
form y = kx where k is some constant. charting retardation ability
against temperature.

>
>> no straight
>> line graph that starts with retardation ability being at max when the
>> temperature is some 'cold point' that we should take to be air ambent
>> temp, with retardation ability dropping in direct response to
>> temperature increase.
>
>dude, you're turning speed into heat. if the brakes fade more as the
>temperature rises, and they do, you want the initial temperature to me
>minimized.

yes, i notice your phrasing, "*IF* the brakes fade more as the
temperature rises" they do, but its not a straight line graph. You
don't have maximum retardation at 20C, and complete failure at say
300c, and at 150C they're only at 50% strength.

>
>> There is instead a gradual decrease from the
>> brak systems optimal temperature (whichis NOT air ambient) to the 'max
>> operating' and then a more rapid decrease.
>
>so what is "optimal" for a normal car braking system??? and there's no
>physical way brake temperature can decrease if you're dumping kinetic
>energy into them.

Lets use the tank analagy. Its one often used to illustrate energy
changes. You have a water tank, and you have a tap, or hose, that puts
water into that tank. the water is the amount of thermal energy. if
the tank has a number of perforatiosn in it, to allow the water to
leave the tank, is there any way the hose can be running, and yet the
level in the tank decrease? yes, simply, the amount of water leaving
the tank via the holes, can be greater than the amount brought in by
the hose. its a fitting analagy, since the greater the water level,
the higher the pressure, and the faster the water leaves, same as the
radiative and conductive levels of a body to its surroundings
increases as the thermal difference between the two increases - a fact
easily verifyable with a cup of boiling water, a thermometer, and a
watch - just measure the temperature every minute.

>
>>
>>
>>>>You're also on the assumption tha when coasting, people ride the brake
>>>>instead. you know, i've never done that. if i coast, i don't then ride
>>>>the brake, instead i'll make a check application, every so often.
>>>
>>>dude, apart from the fact that coasting is illegal, you're also
>>>indicating you don't have the vehicle under proper control.
>>
>>
>> I asked a friend (a deputy in the next county) and he's never heard of
>> any such law here. Another fact in error/
>
>california vehicle code #21710.
>
>"Coasting Prohibited. The driver of a motor vehicle when traveling on
>down grade upon any highway shall not coast with the gears of such
>vehicle in neutral."

great, thats california, and they have, from experiance, some of the
stupidest, and most politically minded laws there. For isntance, i had
an event out in Long Beach in 99 - mainly gasolene and electricaly
powered vehicles, and the possibility of ONE alcohol powered one.
Because of that possibility, HALF our fire extinguishers had to be
water, and not CO2, because that was state regs. The additive
requirement has already been argued elsewhere on this group in the
last day or two, now they're thinking about (last i heard) certifying
hybrids like the pruis as suitable for carpooling, even with single
occupancy, on the highways. I've already stated elsewhere how modern
diesel vehicles (available in europe, but not the US) get much better
consumption figures than any hybrid can, or does, and yet despite this
easily available, vastly documented fact, the laws are still
considered. One states regulatiosn banning a practice does not hold
for all states. No moreso than, say, west virginia's ban on radar
detectors doesn't make them illegal in the rest of the country.

>
>
>>
>>
>>>>As for the 'not in full control' argument, again, thats from the 50's
>>>>and 60's before the advent of the nice modern synchromesh.
>>>
>>>eh? what has synchromesh got to do with it? that's utterly irrelevant.
>>
>>
>> prior to the synchromesh, when changing gear, entering a gear etc. -
>> it was neccesary to adjust the engine speed to match, to select the
>> gear, and so on. with a synchromesh, its easy to put the car in any
>> gear suitable for the speed of the vehicle. That was the basis of the
>> original 'loss of control' arguments - you had no near-immediate
>> ability to recouple the engine to the wheels.
>
>rubbish. if you can't get the vehicle into gear, whether it's automatic
>or stick, synchro or not [i've driven non-synchro transmissions and
>there's no reason you can't shift if you double-clutch] then either
>you're not competent or the vehicle is defective and shouldn't be on the
>road. again, synchro is irrelevant.
>

irrelevent, you've just proved my point. without it, youll have to
double-clutch, taking time, and some thought, meaning att he critical
time, you're not placing full concentration on avoidance, as you're
attempting to match engine RPMs. nor can you, as you have called a
requirement and the whole reason its so illegal, slap it into the
lowest gear possible and let the clutch take a heavier load, dumping
it to rob the vehicle of more speed as the energy is transfered to
rotating the engine fast enough to match the wheel speed, throught he
transmission. In an emergency, as you claim this whole thing is the
reason for, this method slows the vehicle substantially quicker than
double clutching, can, or allowing the automatic gearbox to kickdown
on its own. .

>>
>>
>>>>For an
>>>>avoidance measure, engine power or no will make no difference.
>>>
>>>but engine braking does!!! that's why automatics down-shift - for
>>>engine braking and safety.
>>
>>
>> how does engine braking work to increase safety?
>
>because, as mentioned so many times before, it takes a substantial load
>off the brakes!!! it also allows you to instantly re-power the vehicle
>if required.

what substantial laod off the brakes? I think my actual experimental
figures show that at best, they'll work as quarter as well as brakes.
however, they make no difference to the braked stopping distance. In
fact, since the braking is so much quickre than the engine-braked
time, the brakes are actually having to dissipate the inertia of the
engine and flywheel AS WELL.

You can't have a connected system slowing down at different speeds.
the engine wants to slow you from 50mph in about 450ft. the brakes
want to slow you from 50mph in 100ft. therefore the brakes must
dissipate 4x the energy of the engine, and so, for each watt of energy
the engine dissipates, the brakes has to dissipate 3 for the engine.

>
>>
>>
>>>>For
>>>>stopping, your braking speed is limitedby the static friction lmiit of
>>>>the vehicles tyres.
>>>
>>>only if the brakes can supply sufficient friction. if they're toast,
>>>you can have the best tires in the world, but they won't mean a damned
>>>thing to stop you running into that kid that's just kicked their ball
>>>into the road.
>>
>>
>> ok, so let me get your argument straight. engine braking is required
>> because its unsafe to coast. Its unsafe to coast because everyone that
>> does so, does so with badly adjusted and maintained brakes, and
>> insists on riding those brakes to the point of failure whilst
>> coasting. thus when there is an emergency, the small engine
>> retardation effect is then VITAL to stop the car.
>
>no, it's necessary to keep the brakes cool for maximum stopping power.
>remember the temperature delta thing???

really. then why is it, after 6 heavy braking runs, one after another
(to test distance repeatedly for neutral and in gear) could i still do
a 4 wheel lockup on demand. 6 times I'd dumped excessive amounts of
heat, with little ventalation cooling into the brakes (6 stops from
50mph to 0mph, with the resulting lack of airflow over the brakes that
comes with motion) and they hadn't faded. This was both vehicles. No
standard pads, both vehicles at their standard weights, a bit over if
anything, what with the car seats, vcr, tools+fluids in the van, and
200lb of batteries in the back of the civic (lots of lovely hawker
SBS30's- never know when they'll come in handy). They were hot, yes,
faded, no. Both vehicles had standard pads, regular ones from
autozone, civic's changed in december (all 4, plus master cylinder)
and the caravans in march (front only, plus master cyl). Lovely and
humid here too, so when i check the fluid levels, you can be sure they
get some moisture from the air. Brake lines are original, but don't
appear to have any cracks. Heavy loads, lots of heat, possibly wet
brake fluid, not-new pads, still NO FADE. perhaps you ought to rethink
your theory somewhat. I could even probably work out for you the
approximate brake temps after the first run, if you really wanted. I'm
sure that would be 'hot enough' for you.

>
>>
>> I did some tests this adrernoon, using two automatic vehicles, using
>> an old airstrip here. I weighted things in your favour, by using older
>> vehicles (which would have brakes more liekly to fade, and have worn
>> brake systems - a 87 caravan, and an 88 civic. one big car, one little
>> car. Unfortunatly, both are automatics, but on the upside, they have
>> drum brakes with cable-operated handbrakes.
>>
>> I used a speed of 50mph, and attempted a stoping manouver with ONLY
>> engine braking, so as to measure the braking distance, which can then
>> be compaired to a standaised figure, such as ohh, the UK DOT standard
>> braking distances (http://www.highwaycode.gov.uk/09.htm at the bottom)
>>
>> the civic with its 4speed autom box, with me manually downshifting
>> managed to slow to 8mph in 450ft, and wouldn't slow any further. on
>> the second run, engaging the handbrake at 20mph reduced the vehicle to
>> 8mph in 420ft and to a stop in 460.
>> The caravan, with a 3lv6, and 3sp auto, slowed to 9mph in 390ft, and
>> stopped in 430ft with the handbrake application. (well, foot activated
>> parking brake)
>>
>> by constrast, the UK figures show the braking distance to be a total
>> of 120ft, INCLUDING THINKING DISTANCE - not a factor since it was a
>> pre-planned stop point. so, 125ft is the actual stopping distance. so
>> its more than 3x as bad. It gets worse though, since the vehicle used
>> in the uk govt. figures is a 1964 ford Anglia - a car not noted for
>> its agility, and which had a braking system marginally better than a
>> foot operated wooden block pressed to each wheel. Modern cars and SUVs
>> achieve braking distances almost half that. Both vehicles managed a
>> standard braking distance of around 100ft (repeated many times - both
>> with and withouth being in gear)
>
>dude, the engine does not /stop/ the car [unless you turn off the
>ignition]. but it does offer braking in proportion to engine speed
>[which is why you downshift when engine braking] and yet again, this
>reduces the thermal load on the brakes. that's why cars with automatic
>transmissions, like honda, detect when the car is braking and down-shift
>to increase engine braking. i guess you'd never notice that if you
>habitually coast in neutral, but it's fact nevertheless.

well, lets see. i did listen to the engine. under the heavy braking, i
didnt hear it shift once, not in D, or D3 in my civic. Something i
will check tomorow, when its light, is which gears have engine braking
on them. Its something that just poccured to me. The onyl automatic my
father had, was a 1979 ford granada, 2.8 ghia. It had no engine
braking on its 3rd speed.

>
>>
>>
>>>>In fact, you're not having to brake the rotational
>>>>inertia of the engine and connected gearbox componants, so you're
>>>>ahead there too.
>>>
>>>what planet are you on??? look up engine braking on google. truck
>>>manufacturers invest millions in engine braking technology because its
>>>so effective AND SAFE BECAUSE IT DOESN'T OVERHEAT BRAKES.
>>>
>>>
>>>>The only way i can see the engine being of any
>>>>benefit is if you ahve to go FASTER, or a 90dergee+ oversteer
>>>>situation, but in that case, you'd probably want to change from a
>>>>cruising gear in any case.
>>>
>>>eh?
>>
>>
>> whats 'eh' about it. The only way the addition of engine power can
>> assist in any incident is if you are in a spin, or in a situation
>> where you would be required to go faster. In any other case, the car
>> being in gear would no be of any consequence, or positive benefit.
>
>so these situations never occur? you should know that it does rain
>occasionally...

Oh, i know rain very well, being a brit. i know if a lot better than
you do in Sf. The only time you use or need piower still, is to drive
a car out of a rear-wheel slide, and even then only REQUIRED if its
over a certain angle, 30-45deg, depending on car balance. OR to go
faster. In any other situation, excess of power will not help. dynamic
friction (when a wheel is spinning in comparison to the ground, aka a
skid)) is less than static (the normal driving method) and so an
excess of power would not help, except to provide some form of force
tangental to the slide to correct, or for acceration. I think i've
said these two reasons, these ONLY two reasons enough times, in enough
ways for even you to understand.

>
>>
>>
>>>>Regardless, I'm sure we'll be able to go around in circles like this,
>>>>each counter-claiming the other. Instead, i'll send an email over to
>>>>see if Mythbusters will take a look at it.
>>>
>>>be my guest. geeze. i can maybe understand ignorance as an excuse if
>>>the engineering is not understood, but using it as an excuse against the
>>>law??? buddy, you take the prize!
>>
>>
>> Ignorance of engineering is, apprantly, your forte. As is indeed
>> ignorance of the law. If it was so illegal, why did Saab in the 70s
>> sell vehicles that were despigned to freewheel down hills without
>> having to take the car out of gear, you only had to pull a lever i
>> think it was. It was discontinued mainly because most drivers didn't
>> use it, and felt uncomfortable when they did, mainly due to the
>> commonly held misconception you share.
>
>well, funky cv transmissioned daf's & volvos had a button that
>/increased/ engine braking for downhill situations. one of these
>situations does not compute.

i HAD one of theem. A 1986 'rubber band' volvo 340. it wasn't so much
a button that incrased engine braking, it was just one that locked the
transmission ratio to a fixed number. was mainly used for towing, and
hill climbing. I still ahve a 340 in fact, but a 89 manual tranmission
one. Its my work vehicle when i'm in thre UK - love them.

>
>>
>> This, like any long term myth, is one that clearly won't go away after
>> having being delt with in common sense. In short, you say that if you
>> coast down any hill, you must coast down all (can't pick your
>> situation, as you call it) and you must ride your brakes at al times.
>
>you're the guy riding brakes. i use the engine.

i'm not now, nor have i ever ridden brakes. show me where i said i
have. You're the only one that can't seem to understand that the only
way to coast is to then ride your brakes. Who can't understand that
you can instead let your vehicles momentum incrase, just as if you
were using your accelerator slightly down the hill.

>
>> Oh, and you have an old brake system, that's been poorly maintained,
>> so they would fade to nothing (despite the fact it would fail at the
>> 50mph braking test above, due to the greater heat generation vs
>> dissipation, on your straight-line temp-retardation graph) and that in
>> an emergency, a braking system that has no effect on actual
>> deceleration under proper braking, and which has very poor
>> deceleration figures when used on its own is not only usefull, but
>> legally required to be used. Would you care to attempt to refute these
>> facts, maybe do some measurements of your own with your own vehicles.
>> Maybe even employ some simple logic.
>
>no. you're using twisted logic to put utterly incorrect words in my
>mouth. the physics are very simple: a brake turns kinetic energy into
>heat. as the temperature rises, the ability to continue turning k.e.
>into heat falls. let me know if you can grasp that concept, then we can
>continue this discussion.

Oh, i understand the concept just fine. Lets see if you can grasp the
more basic one. coasting, does not require riding the brakes. if the
hills incluide is such that you must ride the brakes, you don't coast.
its a judgement thing, Clearly you have no judgement.

Here's another thought to ponder. By your definition, push-starting a
vehicle, is not only illegal, but impossible. illegal because push
starting is, at its basis, coasting, and then putting the car into
gear. This is clearly illegal all over the world, since theres a law
about it in California. Secondly, its impossible because, whilst
caoating, you have your foot on the brake, riding it. You ride your
brakes when people are giving youa push, and they'll wake your *** up
in a hurry.

When you can get THAT concept, that coasting does not require riding
the brakes, that continuance of a limited speed is not the aim, rather
the utlisation of the concervation of momentum, , then by all means
post back. If you still haven't grasped that, then don't bother.

 

On Mon, 22 Aug 2005 01:18:02 GMT, "Elle"
<elle_navorski@nospam.earthlink.net> wrote:

>"jim beam" <nospam@example.net> wrote
>> it's not misinformation, it's dead accurate. brakes linings /do/ over
>> heat, brake lines fail, brake fluids boil, speeds can become excessive,
>> and you are not in full control of the vehicle in the event you need to
>> make any evasive manoevers. it's bad for the transmission too. do not
>> ever coast in neutral down a hill! /EVER/!
>
>When you admit you have ceased to speed on a regular basis, then you might
>be worth listening to when it comes to safety issues.
>
>Quit freaking out over casual coasting. If you must whine, whine out riding
>the brakes.

To him, it seems the two are one and the same. If you're in neutral
down a hill, you MUST be riding the brakes. Your brakes must also be
in poor condition, have parts replaced with below spec cheap and/or
unsuitable parts, or be from 40+ years ago.

Hes got no clue.

>

 

"jim beam" <nospam@example.net> wrote in message
news:xPqdnWEAG9f5qpTeRVn-tQ@speakeasy.net...

> those are carbon fiber brakes. they're banned for road use

In what juristiction are they banned?


>> So, i can't pick when i'm going to coast? My gearbox has a life of its
>> own?
>
> not legally, no. how many times do you need to be told? if you have an
> accident and the cops investigate, they'll throw the book at you. assuming
> you don't run into me of course, in which case the cops would be the least
> of your concerns.

Do you have a citation for this?

 

"flobert" <nomail@here.NOT> wrote
> <elle_navorski@nospam.earthlink.net> wrote:
>
> >"jim beam" <nospam@example.net> wrote
> >> it's not misinformation, it's dead accurate. brakes linings /do/ over
> >> heat, brake lines fail, brake fluids boil, speeds can become excessive,
> >> and you are not in full control of the vehicle in the event you need to
> >> make any evasive manoevers. it's bad for the transmission too. do not
> >> ever coast in neutral down a hill! /EVER/!
> >
> >When you admit you have ceased to speed on a regular basis, then you
might
> >be worth listening to when it comes to safety issues.
> >
> >Quit freaking out over casual coasting. If you must whine, whine [about]
> > riding
> >the brakes.
>
> To him, it seems the two are one and the same. If you're in neutral
> down a hill, you MUST be riding the brakes.

Yup. But the guy's not stupid. His ego is preventing him from admiting a
post-o.

He likes to lecture about safety, then admits he speeds or rides his bicycle
in heavy traffic. Go figure <shrug>.

> Your brakes must also be
> in poor condition, have parts replaced with below spec cheap and/or
> unsuitable parts, or be from 40+ years ago.

Among other things already mentioned, like a _very_ long, steep, grade is
needed to raise the likelihood of a brake malfunction to something
meaningful.

You're wrong on this one, Jim.

 

On Mon, 22 Aug 2005 00:47:45 -0400, flobert <nomail@here.NOT> wrote:

<heavy snipping done before and after, to get to the cux>

>>
>>no, it's necessary to keep the brakes cool for maximum stopping power.
>>remember the temperature delta thing???
>
>really. then why is it, after 6 heavy braking runs, one after another
>(to test distance repeatedly for neutral and in gear) could i still do
>a 4 wheel lockup on demand. 6 times I'd dumped excessive amounts of
>heat, with little ventalation cooling into the brakes (6 stops from
>50mph to 0mph, with the resulting lack of airflow over the brakes that
>comes with motion) and they hadn't faded. This was both vehicles. No
>standard pads, both vehicles at their standard weights, a bit over if
>anything, what with the car seats, vcr, tools+fluids in the van, and
>200lb of batteries in the back of the civic (lots of lovely hawker
>SBS30's- never know when they'll come in handy). They were hot, yes,
>faded, no. Both vehicles had standard pads, regular ones from
>autozone, civic's changed in december (all 4, plus master cylinder)
>and the caravans in march (front only, plus master cyl). Lovely and
>humid here too, so when i check the fluid levels, you can be sure they
>get some moisture from the air. Brake lines are original, but don't
>appear to have any cracks. Heavy loads, lots of heat, possibly wet
>brake fluid, not-new pads, still NO FADE. perhaps you ought to rethink
>your theory somewhat. I could even probably work out for you the
>approximate brake temps after the first run, if you really wanted. I'm
>sure that would be 'hot enough' for you.
>

Ok, i just spent the last half hour or so getting some figures to
match to my facts.

The difference in values for the figures for a fast emergency stop to
zero, and for riding the brakes was even greater than i thought. and
to vastly simplify the maths (so i comfortably got the entire set of
calculations on s single sheet of paper, i even made many assumptions
in your favour. Lets see them brakes burn!.

I'm using for the vehicle, my 88 honda civic DX - partly since its
relevent, this being a honda group, but also because i had the figures
for it to hand, unlike the caravan, and its been so much longer since
its brake service (which plays to you)

Mass, approximatly 1000KG (2200lb) Its about right, and makes a nice
easy figure for calculations. for the rapid braking, i'll use the
50mph distance from yesterday, but attribute itt o a speed of 55mph -
eases to your argument, since its more energy dumped into the brakes,
and saves me calculating too many values. For the 'coasting and riding
your brakes' which i'll call 'coasting' now, I used the model of the
hill on US19 that i've previously mentioend. cresting the hill at
55mph, in gear the engine braking keeps the speed at 55mph, or
thereabouts, unchecked it gets to about 65mph, in the distances of
about 1 mile. Thus, i'll call the difference in KE between 55mph and
65mph (now see why i picked 55mph as the speed for the braking
distance above) as the amount dumped into the brakes, or engine going
down a hill.

Kinetic energy: (1/2 Mv^2)
brake - 0.5 x 1000 x 24.5872^2 (using meters/sec)
= 302,265.2 J
coast - 0.5x 1000 x 29.6576^2 - 302265.2
= 422172.05 - 302265.2
= 119,906.85 J

Hmm, the coast energy is only just over 1/3 the brake energy. Oh dear,
not looking good for your argument...

Lets see about how much energy per second is put into the brakes per
second. I'm assuming, of course, that the vehicle only has front
brakes. Again, simplifies for me, and is biased towards your claims.

assuming a linear speed decrease - it isn''t, i know, but as its a
quadratic decrease, divide it by your straight line assertation of
brake performance decrease with temp,a nd it comes to a near linear
line

55-0 mph in 100ft is a time of 2.47sec. 55mph to cover 1 mile is 65.44
seconds.
joules per second works out as
brake - 302265.2 / 2.47 = 122374.57 J/s
coast - 119906.85 / 65.4 = 1832.3174

Hang on, notice something there? in one second, the emergency stop has
absorbed more energy than over the entire run of the coast. Odd...

Now, i mentioned temperature just before. how hot will it get? Again,
for simplicity, all the energy is going into heating the brake discs
only. There is NO cooling effect allowed for. This HEAVILY favours
your arguments, and this is where you win through, clearly. The weight
of each brake disc for a honda civic is 10lb, or 4.54Kg. The specific
heat capacity of cast iron is 460J/Kg/K - or, in other words, for
every 460J of energy put into it, 1Kg of cast iron will be raised 1
Kelvin (or 1 Centrigrade) in temperature. Lets dump those energies in,
shall we? Remember, 2 discs, (or rotors if you will) so 9.08kg

lets see then
brake - (302265.2 / 9.08) / 460 = 72.36K rise.
coast - (119906.85 / 9.08) / 460 = 28.70K rise.

Lets say the ambient temperature here in georgia was 90F, or 32.2C. We
add those figures, and what do we get?

brake - 104.2C - 219F
coast - 60.9C - 141F

look att hat, If we used water as our brake fluid, assuming it was run
right onto the disc, it would have boiled.

What are the boiling points for brake fluid?
acording to govt. specs, the WET boiling point of DOT3 brake fluid
(3.7% h2O by vol) is 284F - significantly higher than the maximum
possible temperature of any braking componant in these tests.

in short, your claims and assertations are utter bullshit. I've given
the amth, worked it through. Where i've had to approximate, i've done
so heavily biased in your direction (front brakes only, no cooling,
all temperature udmped into one comonant only) and even then they were
a ways away from failure point. As I said, only very badly maintained
brakes would fail the way you claim happens, and only then if you
heavily ride the brakes as you coast, and if that were to happen,
you'd be a lot more ed if you had to do any kind of emergency
stop. Just as an aside, any ideas what sort of speed that coast energy
figure represents? just 35mph. So, a car that has the braking from
35mph over a mile and still has brake failure - sounds like
you've got a lot of problems there.

thats the brake failure utterly annihilated, even for your claims that
you have to be riding the brakes. AS for 'full control' - the only two
manouvers, as i've said before now, is aceleration (which was what you
were trying to counter with your engine braking anyway) and to correct
rear wheel skids. anything else you do NOt want the application of
power, and thus having the engine connected to the wheels is
meaningless.

hope i've enlightened you with how things actually, numerically work
in the real world, or even in heavily biased 'jim beam world'. If you
can prove any factual, or numerical problems with my figures, then go
ahead, if not, why not act like a man for onec, and actual admit you
were wrong.

 

flobert wrote:
<snip>

dude

if i've been short tempered or even rude, i apologize. i'm really not
interested in personalizing any disagreement, so in future, let's just
try and stick to the tech stuff. and i'm pushed for time right now, so
i'm not in a positon to do a point-by-point review of your posts, but i
hope to get back to you later in the week. meanwhile, other than to say
that your "filling tank" analogy is absolutely on-target and that i
disagree with a lot of your other stuff, check out the following:

http://encyclopedia.laborlawtalk.com/disc_brake
http://www.whnet.com/4x4/brakepads.html
http://www-personal.engin.umich.edu/...animation.html
http://www.e-z.net/~ts/ts/Brakfade.htm

 

On Mon, 22 Aug 2005 20:17:48 -0700, jim beam <nospam@example.net>
wrote:

>flobert wrote:
><snip>
>
>dude
>
>if i've been short tempered or even rude, i apologize. i'm really not
>interested in personalizing any disagreement, so in future, let's just
>try and stick to the tech stuff. and i'm pushed for time right now, so
>i'm not in a positon to do a point-by-point review of your posts, but i
>hope to get back to you later in the week. meanwhile, other than to say
>that your "filling tank" analogy is absolutely on-target and that i
>disagree with a lot of your other stuff, check out the following:
>
>http://encyclopedia.laborlawtalk.com/disc_brake
>http://www.whnet.com/4x4/brakepads.html
>http://www-personal.engin.umich.edu/...animation.html
>http://www.e-z.net/~ts/ts/Brakfade.htm

Whats more to say, the maths is there. Its broken down simply. Its
heavily biased towards your degrees, and it STILL doesn't come close
to your predictions of doom.

Taken a car, made it stop from a faster speed, using front brakes
only, eliminated cooling, eliminated heat dissipation, eliminated heat
, and its still only equating a 35mph stop.

you're talking . If you can disprove the maths, do so. You can't
get more 'tech stuff' than simple mathematics and physics. You know,
energy calculations. I'm Kinda busy at work myself too - you know, got
car designs to work on, funnily enough, i start work ona braking
system on thursday. The maths though i purposefully kept simple, just
so you could follow it - took me less than half an hour, start to
finish, and that included getting references. Any website you care to
try and use, as a reference will actually detract from your argument.
theyll point out heat dissipation, ablation energy disipation, thermal
transference, ventilation and all those other things which DROP the
temperature of the brakes from the peak temp.

None of this matters though, as you still claim that riding your
brakes as a check speed causes excessive heat buildup and failure. As
i more than amply demonstrated, all things being equal, the braking
energy required to keep a vehicle at a speed when it would normally go
faster is insignificant in reference to any form of sudden stop. in
short you say that putting 1832J of energy into a braking ssytem per
second leads to failure - equivilent to a stop of 2mph.

You'd best get back to work though, must be time for you to change all
the oil at the McD's you work at. You sure as hell don't work in any
technologically related field.

 

On Mon, 22 Aug 2005 20:17:48 -0700, jim beam <nospam@example.net>
wrote:

>flobert wrote:
><snip>
>
>dude
>
>if i've been short tempered or even rude, i apologize. i'm really not
>interested in personalizing any disagreement, so in future, let's just
>try and stick to the tech stuff. and i'm pushed for time right now, so
>i'm not in a positon to do a point-by-point review of your posts, but i
>hope to get back to you later in the week. meanwhile, other than to say
>that your "filling tank" analogy is absolutely on-target and that i
>disagree with a lot of your other stuff, check out the following:

Oh, i checked out your links too

>
>http://encyclopedia.laborlawtalk.com/disc_brake

Factually incorrect in many areas. A good example was the MMC piece,
which is WAY off the mark. The MMc brakes didn't require a high
temperatureand ran cooler, due to the differing method of ablation
used. The manufacturer is still very much in operator (and theres not
just one, there's many) the reason for the change was for reasons of
cost. The first few thousand were done 'cheap' but after the initally
licensed 2000 sets, the full costs were passed onto lotus. Hence after
chassis number 3700-ish, they switched perminantly back to cast iron
discs. Oh yeah, there was also some question of wet operational
ability.
http://www.elises.co.uk/components/s1/brakes/ is a better link on that
detail, for instance.


>http://www.whnet.com/4x4/brakepads.html

A sales page about a new 'type of brakepad' - basically one that has
an integrated anti-squeal shim, whoopie.

>http://www-personal.engin.umich.edu/...animation.html

This is the only one of any relevence. It does show a disc getting to
the point of DOt3 wet boil after appoximatly 36 seconds. i have sent
an email to Prof barber (and as a fellow brit, he'll help me out
(especially as i believe i have a friend who was studying mechanical
engineering at cambridge at the same time as him) and i'm sure we'll
find that he was putting excessive braking loads throguh a single
disc. I wouldn't be surprised if he was simulating at least twice the
load that i calculated. I'm sure he'll drop an email back to me in the
next day or so.

>http://www.e-z.net/~ts/ts/Brakfade.htm

Drum brakes, utterly irrelevent. Thermal masses and mass ratios, plus
heat dissipation figures are massivly different to those of disc
brakes. Also, unless i'm very much mistaken, drum brakes haven't
provided more than about 40% of braking ability in any vehicle made in
the last 30 years.

in short, what little research you have done has turned up one usefull
page, which is basically a thermal buildup animation, with no
accompanying data. Thus whilst it is contributory, and shows how the
heat builds up, it doesn't explain under what conditions this buildup
of heat over time occurs. Persoanlly, i'm betting its a static jig, as
in no ventilation. Again, we'll wait and see.

 

flobert wrote:
<snip>
>
> Ok, i just spent the last half hour or so getting some figures to
> match to my facts.

"getting"? you didn't do them yourself?

>
> The difference in values for the figures for a fast emergency stop to
> zero, and for riding the brakes was even greater than i thought. and
> to vastly simplify the maths (so i comfortably got the entire set of
> calculations on s single sheet of paper, i even made many assumptions
> in your favour. Lets see them brakes burn!.
>
> I'm using for the vehicle, my 88 honda civic DX - partly since its
> relevent, this being a honda group, but also because i had the figures
> for it to hand, unlike the caravan, and its been so much longer since
> its brake service (which plays to you)
>
> Mass, approximatly 1000KG (2200lb) Its about right, and makes a nice
> easy figure for calculations. for the rapid braking, i'll use the
> 50mph distance from yesterday, but attribute itt o a speed of 55mph -
> eases to your argument, since its more energy dumped into the brakes,
> and saves me calculating too many values. For the 'coasting and riding
> your brakes' which i'll call 'coasting' now, I used the model of the
> hill on US19 that i've previously mentioend. cresting the hill at
> 55mph, in gear the engine braking keeps the speed at 55mph, or
> thereabouts, unchecked it gets to about 65mph, in the distances of
> about 1 mile. Thus, i'll call the difference in KE between 55mph and
> 65mph (now see why i picked 55mph as the speed for the braking
> distance above) as the amount dumped into the brakes, or engine going
> down a hill.
>
> Kinetic energy: (1/2 Mv^2)
> brake - 0.5 x 1000 x 24.5872^2 (using meters/sec)
> = 302,265.2 J

first, for this to be a safe vehicle, you have to assume max gross
vehicle weight [mgvw]. that's ~3000lbs or 1363kg. the brakes are no
good if they can't stop the vehicle when fully loaded.

that's KE = 0.5 x 1363 x 24.5872^2
i.e. 412,180J from your 55mph velocity.

> coast - 0.5x 1000 x 29.6576^2 - 302265.2
> = 422172.05 - 302265.2
> = 119,906.85 J

to clarify & grossly simplify, "coast" is the _additional_ energy that
needs to be dissipated by the brakes if it's not being dissipated by
engine braking.

using mgvw, KE = (0.5 x 1363 x 29.6576^2) - 412,180
i.e. 599,429 - 412,180 = 187,249J is dissipated by engine braking.

>
> Hmm, the coast energy is only just over 1/3 the brake energy. Oh dear,
> not looking good for your argument...

not sure you understand the concept, but let's continue...

>
> Lets see about how much energy per second is put into the brakes per
> second. I'm assuming, of course, that the vehicle only has front
> brakes. Again, simplifies for me, and is biased towards your claims.
>
> assuming a linear speed decrease - it isn''t, i know, but as its a
> quadratic decrease, divide it by your straight line assertation of
> brake performance decrease with temp,a nd it comes to a near linear
> line
>
> 55-0 mph in 100ft is a time of 2.47sec. 55mph to cover 1 mile is 65.44
> seconds.
> joules per second works out as
> brake - 302265.2 / 2.47 = 122374.57 J/s

ok, let's just get back to mgvw, so we have:
412,180J / 2.47 = 166,874W

> coast - 119906.85 / 65.4 = 1832.3174
>
> Hang on, notice something there? in one second, the emergency stop has
> absorbed more energy than over the entire run of the coast. Odd...

this is way off. the "coast" is the energy difference. you're not
trying to calculate the energy dissipated by just drifting along, you're
trying to calculate how much difference engine braking makes to brake
temperature.

per the above, if the engine is not braking the car, you need to
dissipate an additional 187,249J / 2.47 = 75,809W. this is a GROSS
simplification ignoring wind, friction, etc., but it'll do for first order.

>
> Now, i mentioned temperature just before. how hot will it get? Again,
> for simplicity, all the energy is going into heating the brake discs
> only. There is NO cooling effect allowed for. This HEAVILY favours
> your arguments, and this is where you win through, clearly. The weight
> of each brake disc for a honda civic is 10lb, or 4.54Kg. The specific
> heat capacity of cast iron is 460J/Kg/K - or, in other words, for
> every 460J of energy put into it, 1Kg of cast iron will be raised 1
> Kelvin (or 1 Centrigrade) in temperature. Lets dump those energies in,
> shall we? Remember, 2 discs, (or rotors if you will) so 9.08kg
>
> lets see then
> brake - (302265.2 / 9.08) / 460 = 72.36K rise.

the running surface of the disk, the bit that gets hot, is less than
that because the 10lbs includes the hub part, not just the rotor. that
does not heat significantly for this first order calc, but hey...

so, with mgvw, that's 412,180J / (9.08lbs x 460) = 99K rise.

> coast - (119906.85 / 9.08) / 460 = 28.70K rise.

with mgvw, that's 187,249J / (9.08lbs x 460) = 45K rise.

that gets /added/ to the rise in disk temp if you're coasting because no
energy is being dissipated by the engine.

>
> Lets say the ambient temperature here in georgia was 90F, or 32.2C. We
> add those figures, and what do we get?
>
> brake - 104.2C - 219F
> coast - 60.9C - 141F

make that:
131C for normal braking, and
176C without additional engine braking
but neither are anything too serious given that we're talking single
application.

>
> look att hat, If we used water as our brake fluid, assuming it was run
> right onto the disc, it would have boiled.
>
> What are the boiling points for brake fluid?
> acording to govt. specs, the WET boiling point of DOT3 brake fluid
> (3.7% h2O by vol) is 284F - significantly higher than the maximum
> possible temperature of any braking componant in these tests.

that's true, for one single stop, from cold. here's where we get to the
point, and where your water tank analogy comes in: you don't just
operate a brake once. for example, like my descent of filbert st,
coming to a halt at each stop sign. each time you brake, you "fill the
tank". particularly if you're at mgvw. now we need to figure out how
quickly is the heat "leaving the tank"? in other words, to what already
existing disk temp are you now adding your delta T? you want to take a
shot at the heat dissipation rate? [hint: it's /less/ than the heating
rate.]

>
> in short, your claims and assertations are utter bullshit. I've given
> the amth, worked it through. Where i've had to approximate, i've done
> so heavily biased in your direction (front brakes only, no cooling,
> all temperature udmped into one comonant only) and even then they were
> a ways away from failure point. As I said, only very badly maintained
> brakes would fail the way you claim happens, and only then if you
> heavily ride the brakes as you coast, and if that were to happen,
> you'd be a lot more ed if you had to do any kind of emergency
> stop. Just as an aside, any ideas what sort of speed that coast energy
> figure represents? just 35mph. So, a car that has the braking from
> 35mph over a mile and still has brake failure - sounds like
> you've got a lot of problems there.

ok, let's get to the links i posted.

if you'd bothered to scroll to the bottom of this page:
http://www.whnet.com/4x4/brakepads.html
you'd see this:
http://www.whnet.com/4x4/pix/hot_brake.jpg

that looks remarkably like a disk that's exceeded 176C to me. how could
that possibly be? [rhetorical]. easy, multiple brake applications that
"fill the tank", just like the one i described to you for filbert st.

and let's look at this:
http://www.e-z.net/~ts/ts/Brakfade.htm
that graphic shows brake fade. you try to assert it's "irrelevant"
because it happens to mention drums, not disks. that's an
extraordinarily incorrect statement considering that the friction
material and the drum material in both systems is identical and their
friction characteristics are temperature dependent in exactly the same way.

disks don't get hot? from:
http://encyclopedia.laborlawtalk.com/disc_brake
we have:
http://encyclopedia.laborlawtalk.com/Image:1901.jpg
now, that's a stretch because it's a racing car driven to the limit, but
the disks still look warm to me. [i initially included the article for
the carbon disk discussion, since you raised them.]

finally, from:
http://www-personal.engin.umich.edu/...animation.html
we have the animated disk warming measurement where delta T is shown
settling at 236C after peaking at 242C. this exceeds your worse case
scenario, and still does not approach the temperatures seen in the links
i've just posted. did you notice hot the temp rise starts at 98C?
that's only possible if the time for heat dissipation to ambient is
somewhat slower than the period to brake re-application, i.e. real world
usage.

>
> thats the brake failure utterly annihilated, even for your claims that
> you have to be riding the brakes. AS for 'full control' - the only two
> manouvers, as i've said before now, is aceleration (which was what you
> were trying to counter with your engine braking anyway) and to correct
> rear wheel skids. anything else you do NOt want the application of
> power, and thus having the engine connected to the wheels is
> meaningless.
>
> hope i've enlightened you with how things actually, numerically work
> in the real world, or even in heavily biased 'jim beam world'. If you
> can prove any factual, or numerical problems with my figures, then go
> ahead, if not, why not act like a man for onec, and actual admit you
> were wrong.

now, to be fair, i acknowledge that your opinion may be colored by your
never having experienced brake fade, particularly if you live in
flatlands that surround airfields and drive a well-braked car like a
lotus elise, but to say fade does not happen is simply incorrect.

let's just re-state some facts for the record:

1. fade can and does happen.

2. brake heating is exacerbated by not taking advantage of engine braking.

3. fade is partly dependent on brake materials.

4. fade is partly dependent on the rate at which a brake component can
be cooled.

i have personally seen brakes on a normal family sedan glow red after
repeated emergency braking tests. i can personally attest to these hot
brakes exhibiting significant fade. i have cited links that evidence
both fade and highly elevated brake temperatures. if you've never seen,
experienced or don't care to believe, hey, good luck to you.