In a message dated 4/22/02 9:57:04 AM Central Daylight Time,
woods@mae.uta.edu writes:
<< Good discussion. I would like to clarify one thing. You said >>
>If you had unlimited power available, you should be able to make the top
>of the friction circle fill in similar to
>the bottom. Obviously, brakes have more "power" than the engine.
<< This statement is true only for well-balanced 4-wheel drive cars. In
two-wheel drive cars, only two tires are contributing to acceleration
whereas four tires are contributing to braking. >>
Yes, I skipped this point, that is what I get for writing while half asleep.
<< Each tire can only hold a
certain amount of force before it breaks loose. Therefore, considering
weight transfer, a rear-wheel drive can get about 70% of its braking g's
and a front-wheel drive car can get about 40% of its braking g's in
acceleration. These numbers depend upon weight distribution, CG location,
wheelbase, and g's of acceleration. >>
Your numbers very close to what I have seen. Our 95 Celica, at VERY low
speeds in first gear, would just hit about .4 G before wheel spin, and my
beast turbo rear drive Celica with 300 hp has hit over .65 G acceleration in
second gear before wheel spin. It sure would be nice to hit 70, and I think
the car can do it. Too much camber on the rear tires is hurting a bit.
<< I agree with you that brakes have more "power" and my observation is most
folks don't use enough brakes. If your braking g's don't match your
lateral g's, then you need to adjust the brake bias or just use more
brakes... cheapest trick to faster times. >>
I know I never trust the brakes enough. Geez slaps me in the face with that
every run. Just yesterday at our eevnt, we had WET conditions, and it made
for serious fun diving into the braking zones from over 60 mph. For the wet
conditions, I was just about reaching lockup at all four wheels together. It
was no where near 1 G on the water though. On dry pavement, I seem to lock
fronts first, but I have no easy to adjust brake bias control. I have messed
with different brake pads fron to rear to balane it some, and it is far beter
now. Carbotech greens on the back is way too much rear brake on my car.
<< Incidently, if you like "math", my book "Modeling and Simulation of Dynamic
Systems" from Prentice Hall has a complete analysis of a braking system and
how to calculate the bias bar setting in Chapter 10. >>
I'll have to take a look. My libraray of car tuning books is getting pretty
good, but you can never have too much info.
<< -Dr. Bob Woods
University of Texas at Arlington >>
Well, I am not a Dr., I just study this stuff for my own knowledge. I helped
my friend work on his SAE car back (oh wow) 17 years ago. My field of work
has nothing to do with cars. I design, install, and service movie theatre
projection and sound systems. I have now helped build and tune about 5 cars.
I found Geez and driving schools are a much bigger performance improvement
than $1000 shocks.
Gary M.
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