@Sorcerer: I remember your sample where the wheels got stuck in certain conditions after jumping from a high cliff. There's nothing I can do about glitches that can not be reproduced reliably. If your car is constantly stuck in the ground (as in the videos) then I can debug it and find the source of the problem.
The Racer source code has been updated to work with 6.40.x and the car does not get stuck there. By looking at the differences between that implementation and your own you should be able to determine which parameters need to be adjusted to prevent these glitches.