These springs have become the "standard" in BMW Club racings JS class - We designed these springs around BMW's own Group N springs. BMW's springs were designed to compete in Europe's production-based Group N racing series. Our springs are a progressive-rate spring with a range from 200 lb/inch up to 900 lb/inch. There is also a large ratio of rear to front stiffness which will help eliminate understeer. These springs will lower a stock M3 by about 1.50" front and 1.25" rear but they work on any E30. Although you can buy these springs as only a set, we strongly recommend installing in conjunction with our modified Bilstein shocks at the same time.