Is there an easy formula to figure out DS lengths when you lift a vehicle before doing so? My Sami has a SPOA high pad lift and I have a chance to get 4" springs for next to nothing. My old springs are negative arch now and the on road handling is horrible. I currently have DS spacers but was thinking that I would need to lengthen my DS's when I add 4" more. Is this true and if so how much?