car is under my terrain

hi...
i started to use OgreBullet
i read some tutorials and examples, and tried my first application...
my problem is:
when I use HeightmapCollisionShape for terrain in my project my car hides under some parts of the terrain, and climb it perfectly other parts...
although I defined the collision shape for this object ....
i tried making the tiles size of my terrain too small (17) in order to make my terrain more punctual...
my terrain is smooth but i wonder why my car disappear under some hills?
is there some thing i missed? or pararmeter that makes collision with the terrain better?
thanks in advance...

It sounds like your terrain collision mesh is not matched to your visible terrain. The sample code that comes with Ogre Bullet will show you how to use a height map to generate your collision mesh, assuming you use the same height map to generate your visible terrain.

- Fish