how to make tank never come off the terrain

HI i got a question, how can my tank never come off the terrain. When i am driving on about 50km/h and I am starting steering my tank is comming off the terrain. I have assigned rigidbody, and Center of mass to my vehicle but, as I see they did not affect. Here is image about what i exactly want:
This is what usually happens:
32157-1.png
and this what I need:
[32158-i+am+stoped.png|32158]

Try to put your Center of mass lower then the vehicle.

Increase the tank’s weight.