Sorry for all the recent posts, I'm kind of new to Bullet.
I have a rather large trimesh (makes a car hull - no wheels etc) and whenever it collides with
the ground plane the simulation begins to slow dramatically, like 10 times slower!

Is this due to the number of collisions that are occuring when the trimesh meet the ground plane?
How do i go about speeding up the simulation process, without adjusting the step simulation timing??
NOTE: The trimeshes must be dynamic, not static, so using btBvhTriangleMeshShape probably won't work