Problems like this can sometimes be fixed with the solution in this thread. (I know it’s not exactly the same situation as yours, but the suggestion might still work for you.)
I’ve tried this. I’ve also put a big collider around the car, to make sure that the wheels aren’t touching the walls, but same thing. Sometimes the car jumps. I’ve saw this on other demos too, and others are fine. I just don’t know what else this can be.