My rear springs were a trial and error deal. I started with re-pop XHD leafs on an E. As new they sat too high. With time they sagged low and I realized spring rate was too low. A full leaf added to both sides by my local spring shop fixed both problems. Happy now. FWIW, spring rates in round numbers are 140 lb/in for XHD's and 170 lb/in for XHD + a full leaf.