Bare Knuckle Performance, sprung chain tensionerA secondary (rear wheel) chain tensioner. We all know that rear chain slap; whipping; stretch and regular adjustments comes with the territory. Sounds bad but this automatic chain tensioning device makes the world a better place by keeping a constant tension on the bottom side of the chain for a nicer ride; less maintenance and a longer lasting chain. Note: Requires fitment and welding by a qualified mechanic.