I guess you've seen the warning about not using too many collision-points while adding so much of them..
Splitting it up in several objects would be much better..
I can't see the collision polygon of the tank though and don't know if it's correct in every frame of the animation.
I have seen the warning but i didnt care so its hard to split the round but iwill try to do it . thanks anyway
but if u have seen the wheels are dived into the ground too but i have made their collision to circle
sorry for my bad english