The way I would go about doing it:
1- make certain areas slippery
(almost like a collision detection - try to
detect through progrmamming certain areas)
2- there is a command in the physics where you
can change the friction (in the middle of
the game, too!)
I think it is: ph_setfriction.
do this to the tires.
You can also change the friction
based on the speed of a car (if it is
going a certain slow speed, give it
more friction, if it is going fast,
reduce friction a little)....
Also, I wouldn't use the PlCar01, because you would
manually have to add each vehicle.
I would go to the Wiki and download the newer car physics
that someone made
(although I discoveres 3 problems, it never seemed to get out
of beta - but I figured it out and got it working after about
10-15 hours worth of work)
-Jimc74