The Bilstein B4 2011 BMW Z4 sDrive35is Rear Shock Absorber is a high-performance, monotube gas pressure shock absorber designed to provide superior handling and stability for BMW Z4 sDrive35is vehicles. It features a self-adjusting, deflective disc valving system that provides consistent dampening regardless of road conditions, as well as a high-pressure nitrogen gas charge for improved ride quality. This shock absorber also features a corrosion-resistant zinc finish for long-lasting durability.