How to get the relative distance and velocity of two collision bodies

The novice has encountered problems. After the road model is introduced into unit, rigid body is added to the road surface, wheel collider is added to the wheel. How can the relative distance and relative speed of the wheel and the road surface be obtained when the collision is conducted? After the road model is introduced into unit, a collider is added to the wheel and road surface. How to get the collision when the vehicle is colliding, What about the relative distance between the wheel and the road surface, the relative speed and so on?

read the documentation for the physics.collision class.
Collision class gives you access to all kinds of useful information about the collision that occured.