Wheel springs help

I have a 3d model of a car, I set up the wheel colliders and everything, but when I add a torque to it sometimes it slides off and the angular velocity increases just for a while. That's the first problem, and to move my car I usually use rigidbody.Addrelativeforce and addrelativetorque, but the second question is this, how can I give the impression of a spring between the wheel and the car as if there were a suspension??

Thank you