Multiplier for the extremumValue and asymptoteValue values (default 1).

Changes the stiffness of the friction. Setting this to zero will completely disable all friction from the wheel.

Usually you modify stiffness to simulate various ground materials (e.g. lower the stiffness when driving on grass). See Also: WheelCollider.GetGroundHit.

	// 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;
		}
	}