Hello,I have -85 Z-28 Camaro with Eibach Pro-kit,Koni reds and 17" wheels.Problem is that the rear suspension bottom`s too easy at higher speed`s(120 km/h and up).Here Finnland some roads are bit rough.I think that the rear spring rate are too weak(rear:1st rate 107lbs/in 2st rate 180 lbs/in)Does anybody know what kind spring rate work`s better on my car,and what company make`s them?