The Koni Special Active Shock FSD 05-13 BMW 3-Series (E90) RWD Rear is a performance shock absorber designed to improve the handling and ride quality of the BMW 3-Series (E90) RWD. It features a patented Frequency Selective Damping (FSD) technology that allows the shock to adjust to the frequency of the road surface, providing a more comfortable ride while still providing excellent handling and control. The shock is built with a heavy-duty steel body and features a corrosion-resistant finish for long-lasting performance. It also features a gas-charged design for improved damping and a low-friction seal to reduce stiction.