You wouldn't drive your car for thousands of miles without changing the oil, would you Well, the same goes for the FOX shock on your trusty mountain bike, requiring regular maintenance to keep it operating smoothly. The Fox Rear Shock Rebuild Kit is just what you'll need to keep your FOX Factory Performance or Float X Shock running smoothly on the trail. FOX recommends using this Rear Shock Rebuild Kit for every 125 hours of riding, which means you can usually get away with performing a single rebuild every year, unless you ride a ton throughout the season.