We use UHMW in all our suspension bushings because it is stiff, has almost zero deflection yet also absorbs some vibration. It will outlast other types of rubber or urethane bushings. When the e36 is driven hard on the street & on the track, the rear trailing arms are exposed to extremely large lateral forces. We include black oxide plated steel plates for each RTAB to prevent lateral movement between the bushing material and the aluminum center. Polyurethane and rubber bushings will deflect and slide, causing your rear alignment settings to change mid-corner. With our bushings, you won't have to worry about dynamic changes in your toe settings, the rear alignment stays in check during hard cornering, braking, and acceleration.