Coilover springs are manually adjustable springs which fit over your existing shocks/stucks. There are two type of coilovers. They are true coilovers and sleeve type coilovers. True coilovers are a set up where the shocks have a threaded-body, when as the other one utilize a 'sleeve type' thread. Both allow you to adjust the travel of the spring, typically from 4 inches all the way down to 0 inches. A simple Allen wrench or hex screwdriver is all you need to raise and lower the springs; which raise and lower your car.