We currently don’t support actual collision on the tires. This is something we’re working with NVIDIA to add. The case where the tires are very far from the body is more difficult as it really exposes this flaw. One approach you could take (we do this in the jeep sample game) is to add collision shapes to act as invisible fenders around the tires. This would be extra shapes added to the chassis of the car inside PhAT which you’d have to play with to get it so that it doesn’t hit the ground, but at the same time blocks these bad cases.
We are looking to improve this however so that you can actually get proper blocking behavior from the tires. Not sure how soon we’ll get this in though.
Hope that helps