The Bilstein 14-18 BMW 640i xDrive B4 OE Replacement Shock Absorber - Rear is a direct replacement for the original equipment shock absorber on your 14-18 BMW 640i xDrive. This shock absorber provides superior performance and handling for your vehicle, and is designed to be an exact fit replacement for the factory part. It features a monotube design with a gas-pressurized internal floating piston that provides consistent damping performance. The shock absorber is also designed with a high-pressure nitrogen gas charge that helps to reduce foaming and aeration, leading to improved responsiveness and a smoother ride.