Brakes G60's vs UFO's and other combos............

[Bernie Benz]

Dan, you may wish to rethink your "power logic".  New math, new physics?

> From: Dan Cordon <cord4530 at uidaho.edu>
> Date: Mon, 16 Feb 2004 23:50:05 -0800
> To: 200q20v <200q20v at audifans.com>
> Subject: Re: Brakes G60's vs UFO's and other combos............
> 
>>> I'm no brake engineer, but I
>>>> theorize that if I compare two like kind setups braking with the ABS
>>>> working
>>>> and then not engaging the ABS by modulating the brakes at threshold, I'll
>>>> bet
>>>> the ABS will have a longer stopping distance leading to less heat generated
>>>> on
>>>> the brake rotor and its components.
>> 
>> Not so!  Its the same amount of kinetic energy being converted into heat,
>> independent of the braking system.
> 
> Actually, Scott's right on this one. While it *is* the same amount of
> energy (at least for all practical purposes), the energy is converted in
> a shorter amount of time -- meaning more power. Power is a rate of
> energy flow.
> 
>>> The brakes convert car velocity movement into kinetic heat into the rotor
>>>> during stopping.  The result is, you have generated more brake heat in a
>>>> shorter braking distance.
>> 
>> Your terminology is so screwed up that who is to question?
> 
> In this case, that's not quite right. WE could say that brakes convert
> kinetic energy (from vehicle velocity) in to thermal energy by friction.
> But there is  no more heat generated by stopping faster than stopping
> slow. But since the power is greater, the brake component temperatures
> will be greater.
Not true, if one neglects a very slightly larger heat loss during the
extended breaking time.

Bernie
> 
> Still, this is a pretty small difference in time between ABS stopping
> and threshold stopping, so the power difference is probably negligible.
> 
> I remember when ABS was becoming more common, that most published
> numbers for stopping distance reported that stopping with ABS took
> longer than w/o ABS engaging. However, in more recent magazine articles
> this seems to have switched. Aside from tire lockup w/o ABS, I can't see
> how a car would stop faster with ABS engaged.
> 
> Anyone else notice this?