Subject: What friction is experienced by a car when its brakes are off?

I'm attempting to write a Java simulation for the famous "airplane on a conveyor
belt" problem, to show nontechnical folks what's occurring. One form of the
problem leads to a positive feedback loop, and the conveyor speeds up toward
+infinity until the friction it creates either brakes or breaks the car/plane.
This sort of thing is Very Cool, but requires that I do a better approximation
than just "frictionless wheels." How do car wheels experience and transfer
friction forces to a car when their brakes are disengaged?

Re: What friction is experienced by a car when its brakes are off?