It's definitely not tire related. I'm pretty sure I've put a lot more stress on my end links than you'd get from just having a stiffer tire. I've taken mine out jumping in the desert. Rock crawling. Etc. I've even bent the rear fixed link by dropping it onto a big rock. Bushings are still good at 50k. The only think I've noticed is that the metal straps that are supposed to help hold the bushings on have come off. But other than that - no issues. The folks who are running 20" wheels with lower profile tires have harsher ride than putting on E rated 17" tires. So for example all of the GX's will have firmer tire/wheel combos than an E rated 265/70/17.