i'm going to be roadracing the DA and need a stiffer spring than what I currently have, which is ground control coilovers. I will be mating the new spring to koni yellows that have a modified shorter shock rod. I am wondering what all of you that have had springs custom made had the spring rate set at? The manufacturer will be eibach- their ERS line. Any advice on how to calculate the best spring rate for my application as well as your previous history or knowledge is greatly appreciated