SZ Series - Suspension Shock AbsorberBilstein SZ Series shock absorbers feature a 46mm piston, steel construction and smooth body designed for motorsports applications. These shock absorbers are available in a variety of lengths and standard digressive valve settings that utilize proprietary spring steel valve discs and can be converted to a coilover design (kit sold separately). SZ Series shock absorbers are ideal for racers whose sanctioning rules do not allow or require rebuild