The Bilstein B3 13-17 BMW X3 Replacement Rear Coil Spring is a high-quality aftermarket suspension component designed to replace the factory-installed rear coil spring on the BMW X3. The spring is constructed from a high-tensile steel alloy and features a corrosion-resistant coating to help protect against rust and other environmental damage. The spring is designed to provide a comfortable ride while maintaining a high level of performance, and it is designed to be a direct replacement for the factory-installed spring. The spring also features a progressive rate design, which helps to provide a smoother ride and improved handling.