Coil springs help absorb the wheel movements caused by an uneven road. As the springs react to road changes, the shock or strut dampeners reduce the vibrations of the springs to provide steering and ride stability. The weight of the vehicle is also supported by the coil springs to help keep the vehicle from sagging and causing control issues. This constant compression and expansion can cause the coil springs to wear out or become weak. Other factors like rust or worn out shocks and struts can accelerate their wear. If you notice your vehicle sagging or riding too high or low, check the coil springs. If you need a replacement, it is a good idea to replace the coil springs as a set, including the shocks or struts. O'Reilly Auto Parts carries coil springs, shocks, and strut-related parts for all your suspension repair needs.