The APR Suspension Control Unit (SCU) Upgrade directly replaces your factory suspension controller with a new unit that enables advanced control over your vehicle's factory electronic shocks. The factory controller only operates in a "soft" or "stiff" state with no behavior in-between, despite the incredible capability of the factory electronic shocks. Our controller has advanced programming that takes various inputs to provide fine-tuned control over the shocks in real time. The controller still retains factory comfort and sport functionally, and it doesn't compromise ride quality for performance. However, both modes rapidly increase performance depending on various inputs such as acceleration, brake pressure, G-forces, steering angle, speed, and damper shaft velocity. The experience is absolutely transformative. For the casual driver, the vehicle is more comfortable and rides better than stock. Uncomfortable bouncing and stiffness are reduced, and the car settles faster to provide increased stability. This is accomplished by using the full operating range of the electronic shocks to provide a pleasant experience when you're driving normally. But once you begin pushing the vehicle, the controller quickly adapts to provide performance you never knew was possible from the factory shocks. Even on a straight-line launch the system will help control weight transfer so you can improve your 60ft times for better acceleration and better times in the quarter mile. On a twisty back road, or on a proper track, the controller adjusts each shock individually to provide the grip you need to cut faster lap times with more confidence as the chassis is more balanced. It improves weight transfer on corner turns by allowing a smoother transition, all without the shocks loading the tires, while also reducing overall body roll. Simply put, your vehicle will ride and perform better in every scenario and stays true to our mantra of performance without compromise! Fits Audi A3 Quattro 15-18, A3 Sportback e-tron 16-18, RS3 17-20, S3 15-20, TT Quattro 16-23, TT RS Quattro 18-22, TTS Quattro 16-23