Adding components to 3d models

I want to add a 3d model of a car to my game and controll it. Now i am using a cube from unity as player, with a rigidbody and his collider, so it stays on the ground (plane). But when i import my 3d model, y can add collider to it, but when i add rigidbody component the car go through the ground without colliding. I put a mesh filter and a mesh colllider to the car, but when the rigidbody is turned it doesnt work.

Is the Mesh Collider of the car convex? Setting it to be convex should solve the problem. Non-convex Mesh Colliders with Rigidbody are not supported in Unity anymore.