Using the MM Adjustable Rear Lower Control Arms along with our weld-in upper spring adapter allows the use of standard 2.5" (inside diameter) coil-over springs. Why use coil-over springs in the stock location, on the control arm? Because the coil-over springs have a linear rate, and are available in a much wider range of spring rates. This can help when fine-tuning a car's handling to suit the driver's preferences. This is particularly useful when coil-overs have been installed on the front, but not in the rear of the car. We recommend this setup for track use only; for street use a traditional rear spring is much more suitable.