After alot of work, I have effectively singled out exactly why certain physics entities have a tendancy to have bad collision on terrain! A while ago I posted about bad collision with physics entities and terrain. http://www.conitecserver.com/ubbthreads/showflat.php?Cat=&Number=320317&page=5&view=collapsed&sb=5&o=&fpart=1#320317 You also may remember that I had previously believed the problem had to do with my function names - I was wrong. After much testing, I've come to the the conclusion that the last entity enabled in the physics engine will have faulty collision detection on terrain! Whats weird is that the entites which previously had faulty collision, will suddenly have perfect collision detection, when another entity is enabled into 3dgsPE on terrain. This problem is much more wide spread then I first believed. Upon further testing I noticed that no matter what, whether there is an constraint or no constraint the last entity enabled into 3dgs PE will have faulty collision detection with terrain. Hopefully this will be an easy fix for you Marco. Simply check why the engine gives faulty collision detection between terrain and models which were enabled in the physics engine last. If you have any questions please ask - I know a few others had this problem, and I'll soon release the vehicle code with the "cheap fix".