noob question how to make car stick to ground

ok so i followed a few tutorials and have a car setup where in i have the 3 scripts carsetup.py, powertrain.py and suspension.py… the cars run fine on flat surfaces , but when say while climbing a mountain made from bezier curves, the car jumps all around . i tried to change few values in the scripts but was unable to do anything good with them…

A blend file showing the problem would probably help others to investigate what the problem is exactly.

Ray -z(short distance)------(python)

If own.worldLinearVelocity.z<(threshold):
own.worldVelocity.z=own.worldVelocity.z*.45

If the force is under x, dampen it

thanks. ill give it a go…