Can't change the extremumSlip of a wheel.

I'm simply trying to change the float value of WheelCollider.forwardFriction.extremumSlip at runtime with the following code: WheelColliders [0].forwardFriction.extremumSlip = 0.06f; But apparently I can't do that as I get this error: error CS1612: Cannot modify a value type return value of 'UnityEngine.WheelCollider.forwardFriction'. Consider storing the value in a temporary variable. Any help would be appreciated.