PROGRESSIVE SPRINGS Progressive Springs increase in rate late in stroke to provide additional bottom-out support and open up the use of coil shocks on frames previously only suited to air shocks. As with our Enduro SL springs, these springs are offered in a single free length per rate that fits most shocks from 200 (7.875") to 230mm. They accomodate up to 65mm of shock stroke. A 38mm ID fits our Hazzard shock and Rock Shox models natively, and spacer kits are available to use with other makes and models. Please refer to our Technical Features tab for Spring Rate and Length Information See compatibility on MRP's Coil Spring Spacer page. Some shock length and spring rate combinations require spacers to increase the total effective spring length and engage the threading on the shock body and to account for allowable max preload. Reference the listed free lengths and measure your shock to make sure any spring will fit.