PSi is based in the Motorsports Industrial Park at Sonoma Raceway, (Sears Point) in Sonoma, California. We specialize in Racing Shock Absorbers, Springs, Clutches and Gearboxes. We are a Factory Authorized Sales and Service Agency for all ZF-Sachs shocks and clutches, Koni, Ohlins, Penske, Moton, Bilstein Racing, JRZ & AST shocks.