Progressive Suspension 31-4001 High Performance Fork Cartridge - Lowered True high performance front suspension is finally available for the HD Dyna line. Progressive Suspension has gone back to the drawing board and created a state of the art Fork Cartridge Kit designed to outperform everything on the market. Their new asymmetrical design places a preload adjuster over a progressive rate spring in one leg and an aluminum bodied, sealed cartridge damper on the other. The result is superior damping and ride control combined with tunable preload and a new benchmark for high performance suspension on the Dyna platform Each kit includes components for stock height or 1in. lowered 06-13 Dyna applications