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

Dan Cordon cord4530 at
Tue Feb 17 13:06:28 EST 2004

I'm still going to stick to my initial statement, but amend it with 
this. For all practical purposes, the brake temperature at the end of a 
60-0 mph event will likely be the same with or w/o ABS.

But here's why it *may* not be. Lets look at three separate cases of 
braking - even in the same time. Lets call it 10 seconds to make it easy.

Case 1 - The vehicle slows *very* rapidly at the beginning. With 9 
seconds left the car is barely crawling at 2 mph, and the rotors are 
glowing red hot. Because of the high temperature difference between the 
rotors and the ambient air, the heat will leave the rotors at a faster 
rate. By the time 10 seconds is up, the rotors are not very hot at all.

Case 2 - The vehicle slows so slowly that with one second remaining it's 
still moving at 58 mph. In the last second it stops. At this point. the 
rotors are still glowing red hot (or melted in a puddle) at the end of 
10 seconds.

Case 3 - Consistent deceleration from 60-0. This case will likely yield 
a final temperature somewhere in between.

In all these cases, the energy absorbed *and* average power are exactly 
the same. Neither can be directly correlated to the rotors final 

But back to the original situation, for the cases where there's constant 
(and rapid) deceleration, and one case happens faster than the other - 
the case that brakes harder will have a higher rotor temperature when it 
comes to a stop. But it *may* have a lower rotor temperature than the 
other case by the time the other case comes to a stop. Again, for all 
practical purposes, my judgment says it will be negligible.

There are *far* more variables (like thermal mass of the system, charge 
cooling, etc.) that will effect the brake temperature at the end for a 
given mass and deceleration.

I think we're both agreeing with another on this....but in a strange way.

Bernie Benz wrote:

> Think harder, Dan. 
> Your lesson in "physics phacts" is irrelevant to the point of the
> discussion, that being the relative temperature rise of the braking
> components.  Neglecting the very slight additional heat loss during an
> extended breaking time, the temp rise is independent of time, in the
> practical sense.  Your erroneous initial point, and one that you have been
> backing away from since, was that the temperature rise is not a function of
> the kinetic energy absorbed, but rather the rate of absorbption.
> Bernie

Dan Cordon
Mechanical Engineer
University of Idaho - Engine Research Facility

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