Vsc/trac

wwest · December 7, 2003

Is well on its way to becoming a much greater problem than ABS can/will ever be.

But.

First, VSC (PSM,etc.) is almost always coupled with Trac.

Trac is fairly simple to explain in that all it really does is prevent wheelspin if/when too much gas is being applied for the circumstance. Early versions (92 LS)applied braking to the driven wheels while simultaneosuly dethrottling the engine.

Newer, more modern versions (00 GS) still apply the braking immediately but delay the dethrottling slightly to give the operator time to react and lift the throttle on his/her own.

VSC/Oversteering, more common to RWD.

If the rear is coming around to the right then the right front brake is applied lightly to create a braking "moment", force, counter to the motion of the rear. To the left then the left front brake...

VSC/understeering, more common to FWD.

The assumption would be that you're trying to turn left and the car isn't tracking the steering angle. At the moment there are two different methods in the marketplace for overcoming this problem. One of these is to simply apply both rear brakes on the theory, correct, that slowing the car will always help. The other method is simply the reverse of the over-steering cure, apply a single rear brake to create a "moment", force, this time as an aid to the steering angle.

The problem with all of this is that driver's will see/feel its, VSC/PSM/etc, effect as no different than a new set of tires with a larger contact patch.

Without some feedback to the driver (providing a learning experience) indicating that the car has just approached the "edge", and why, most driver's will simply begin to rely on VSC, again and again, just as they would the bigger contact patch.

One of the reasons I like the ABS implementation is that vibrating brake pedal tells me that the tire/roadbed adhesion coefficient is not up to the task at hand.

Do you know that BMW now has a system that will counter-steer the car, against the driver's steering inputs, if their VSC says the turn is too tight???

Now that's going a bit too far!