The Koni Special Active Shock FSD 02-08 Audi A4 Rear is a performance shock absorber designed to provide superior handling and stability for the Audi A4. It features a unique Frequency Selective Damping technology, which allows for adjustable damping depending on the frequency of the road surface. The shock absorber is adjustable with a knob, allowing the driver to choose between a comfortable ride and a sporty feel. The Koni Special Active Shock FSD 02-08 Audi A4 Rear is designed with a gas-pressurized monotube design, providing a consistent damping force throughout the stroke. It also features a special low-friction seal for improved performance and durability.