The Air Spring is a self-contained unit that replaces your conventional coil spring. You can come up with limitless spring rates, both digressive, and progressive, with one unit. Developed initially for Dirt Latemodels where dual and triple rate spring curves are the norm. This devices eliminates un-needed inventory, and even eliminates bump stops. Bump stops are normally run to generate a progressive rate at max travel, because of the volume, you get a natural progressive spring curve!