Mesh collider makes car fall thru ground at start of game

So when I put a box collider on my car, it doesn’t fall, only the physics are awful. SO i decide to put a mesh collider onto my car, but then the car falls thru the terrain. How can I fix this?

Non convex mesh colliders cannot collide with other non convex mesh colliders. To fix this, either mark your car’s mesh colliders as convex or use multiple box colliders to better approximate the shape of the car.