I solved the problem with a trick: instead putting my outdoor terrain (with cars and physic) inside an hollow block, I applied one of these solutions:
1) I created a solid just below the terrain (covering all the size of the mesh):
terrain: /\/\/\/\/\/\/\/\/\
solid: ==================
2) Second solution is putting 4 small cubes just to the corners of the terrain. See this schema (top view):
[] []
|-----------|
| |
| |
| |
|-----------|
[] []
and left/right view:
[]
====================
[]
This synbol "[]" are the cubes.
The terrain must be inside the virtual area between the cubes.
I hope I was enough clear!
