AirFX Rear Air Ride Magnum shock pair for Harley-Davidson applications The AirFX Magnum shock out performs all other air ride systems in both comfort and durability. Our new shock technology incorporates a double sealed 63mm extra large composite piston. This requires less air pressure and creates a softer, smoother, and consistent ride. The specially designed shock body uses an upper spherical bearing to allow the shock body to pivot in all directions. This minimizes shock side loading or pivot friction while increasing response when cornering. Spacers are provided to custom fit most aftermarket bags. Rebound is set by adding/removing rebound air to the Schrader valve on each shock, allowing the rider to adjust the ride setting.