Yakima Heavy Duty Shocks Increases the carrying capacity of your Yakima- Rack And Roll Trailer Progressive spring rate provide a sturdy and comfortable ride Works on both the Rack and Roll 66 or 78 trailers Increases the Rack and Roll 66 to 250lbs and the Rack and Roll 78 to 300lbs. Do not exceed weight limits. Adjustable, Dual Spring progressive rate, motorcycle-style shock absorbers provide four inches of wheel travel. Independent suspension.