The other Collider the wheel is hitting.
// When attached to the WheelCollider, modifies tire friction based on // static friction of the ground material. function FixedUpdate() { var hit : WheelHit; var wheel : WheelCollider = GetComponent(WheelCollider); if( wheel.GetGroundHit( hit ) ) { wheel.forwardFriction.stiffness = hit.collider.material.staticFriction; wheel.sidewaysFriction.stiffness = hit.collider.material.staticFriction; } }