The coilover springs supplied with my kit are 500# for the front, and 400# for the rear. This compares to the 600# front springs from my previous Mk4. So I assume the difference is because of the sway bar. I can't compare for the rear springs. This is my first IRS build, and I know spring rates for solid axle and IRS are different. Plus I don't know how previous IRS setups compare to the 2015 Mustang setup and geometry. The provided Koni double-adjustable shocks could play into this somehow too.Nice to see the continued evolution of the chassis. Having a front and rear swaybars, and slightly softer spring rates would be nice for the bumper corners.