Manual Collision

I have a sphere (graphic wheel mesh). How Can I avoid it to come thorough track? I can not put collider on it, because it wheel harm wheel collider physic.

This is work great only for flat parts of track.

 dist = w.colider.radius * 0.8f;
             if(Physics.Raycast(w.transform.position, Vector3.down, out hit, dist)) {
             
                 Vector3 newPos = w.transform.position;
                 newPos.y +=  (dist - hit.distance);
                 w.transform.position = newPos;
                 w.isGrounded = true;
              }