Hi 3run,

This kind of problem is quite difficult to solve, as I already encontered it. I think that the problem come from some numerical errors when converting coordinates between gs and physX (Gs values are scaled down when passed to a physX function) and the difference between physX update rate and gs fps. Even some physX 3 demo (vehicle) have jittering problem and they solve this using a lookup table. Perhaps you can also try to change the way you detect the ground. Hope that helps you to find a solution.