The Bilstein B8 2003 BMW Z4 2.5i Rear 36mm Monotube Shock Absorber is a high-performance shock absorber designed to improve the ride quality and handling of the BMW Z4 2.5i. It features a monotube design, which provides better heat dissipation, improved response, and increased durability. It also features a 36mm piston for increased damping control and a gas-pressurized construction for improved ride comfort and stability. This shock absorber is a great choice for those looking to upgrade their vehicle's suspension system.