Could you explain this to me. It says 390 per inch so wouldn't going from 1.9 to 1.8 increase it by 39lbs or is there something I am missing or not understanding?
It’s spring rate times the amount of height decrease or increase PLUS/minus the installed height seat load. So your math is correct. Shimming .100 down is a 39 pound INCREASE in spring load.
.100 is a TON of shims. .060 gets you another 24 pounds. .030 gets you 12.
