Traction Control & Racing

[Rich Vandervoort]

<snip>

What traction control is all about is reducing the power to the wheels,
>or specific wheel, when the tire's adhesion ability is exceeded.  There
>is a lot of potential ways to achieve this, the most common by the OEMs
>is to chop ignition to one or more cylinders in a logical fashion,
>reducing flywheel power.  This is good because while hard on the engine,
>it won't destroy it the same way as cutting fuel to an injector, and
>leaning the hell out of the engine.  BOOM!  There are some who believe
>applying brakes is a good form of traction control - bad - because it
>would be very difficult for a vehicle to determine if its sliding
>forward or sideways, and much to complex to make reliable and cheap,
>which is the OEM goal.  Therefore, applying brakes automatically by an
>ECM could result in a slight slide (driver fuckup) turning into a slide
>off the road over a cliff, into the ocean (worse case).
>
<snip>

Traction control is actually about maximizing traction without upsetting the 
stability of the vehicle.  The traction control system ideally allows just 
enough tire slip to allow the tires to operate at the peak of the 
longitudinal Mu slip curve (usually between 15 and 20 percent).  The reason 
you shut off traction control for autocross, solo, ect. is that so you can 
alter the handling balance with the throttle.  All cars including race cars 
are set up to understeer, by using the throttle on a rear drive car you can 
cut the available lateral grip on the rear tires and make the car oversteer.

Brake traction control is generally used in higher powered vehicles to 
quickly bring slip under control or to redistribute power in a split Mu 
situation.  Lower priced vehicles typically have engine only traction 
control systems because they are very cheap, a little engine code, some code 
in the ABS control unit and hardware to communicate back and forth.  
Traction control intervention will not cause a vehicle to go out of control. 
  Try driving a traction control vehicle on ice and doing donuts; it won't 
do them.  You have to get the car spinning before you hit the throttle, 
since traction control controls longitudinal slip it actually enhances 
lateral grip.  The max lateral grip versus longitudinal slip curve is a 
concave asymptotic curve with a peak of nearly one G at zero longitudinal 
slip and a minimum of zero G at one hundred percent longitudinal slip.

Try beating the stopping distance of ABS on dry pavement.  If you have a 
decent ABS system (not 1st generation or KH) you can not do it.  If you 
don't believe me you get a fifth wheel and try it.  This is possible because 
ABS efficiency is better than your proportioned brake efficiency.

If you have any more questions about ABS or TCS please contact me offline 
via my email address.

Rich V.


_______________________________________________________________
Get Free Email and Do More On The Web. Visit http://www.msn.com