Lowers the rear of your S550 Mustang ;Improves handling and ride quality;980lb/in linear spring rate;Manufactured from chrome silicon high-tensile spring wire;Cold wound on a CNC Coiling Machine to exact specifications;Lifetime warranty against spring sag;Stress-relieved at 750 degrees F;Shot-peened;Computer tested for accurate height and spring rate;Made in the U.S.A.