The Bilstein B3 1999-2003 BMW 528i / 540i / 525i Replacement Rear Coil Spring is an aftermarket suspension component designed to replace the original equipment coil spring on compatible BMW models. This coil spring is designed to improve ride comfort and handling, and to restore the original height and ride quality of the vehicle. The spring is made from high-strength steel and is corrosion-resistant for long-lasting performance. It is also tested and certified to meet or exceed OE specifications.