The Bilstein B4 2006 BMW X5 4.4i Formula 1 Rear 46mm Monotube Shock Absorber is a high-performance shock absorber designed to improve the handling and stability of your BMW X5. It features a 46mm monotube design, which offers superior damping and rebound characteristics compared to conventional shock absorbers. The Bilstein B4 also features a patented digressive piston design, which provides a more responsive and smoother ride. Additionally, it is corrosion-resistant and has a long lifespan, making it a great investment for your BMW X5.