Originally Posted by lucid
I don’t follow you here. Building on your data, assume linear springs and motion ratio = 1, and use a “lowering” spring that barely bridges the perch-perch gap (preload spring compression = 0"; thus, shorter than stock spring), which drops the car by 0.25” (steady state suspension compression = 4.25”). That would result in k = 188 ft lb (800 lb/4.25 in), which is 13% stiffer than stock. So, you can have a shorter and stiffer spring resulting in a net drop over stock.
We're doing exactly the same math. Zero preload, zero drop = 200#, zero preload, 1 inch drop = 160#.
According to the advertising, Eibach drops the front 0.8" (yielding 166#), H&R drops it 1.0 # (yielding 160#) and Dinan drops it 1/2" (yielding 177#).
Dinan is the only one of the three with the opportunity for stiffer than stock springs, and there's no way to know if they actually stiffened them or if they did a shorter stock-rate spring and a smaller pre-load.