The Bilstein B4 2013 BMW X1 xDrive28i Rear Shock Absorber is a high-performance shock absorber designed to improve the ride quality and handling of the BMW X1 xDrive28i. It features a monotube design that provides increased damping power and better control over the suspension. The shock absorber is made from high-quality materials and is corrosion resistant. It is also designed to reduce body roll and improve overall stability.