After a few short uses with 29 inch tires I noticed the rear has unsprung weight on speed humps, could be a huge tire, winch and rear battery and not 100% the XL-7 springs. After I drive it some more with the bigger 31 inch tires I will see if I can pinpoint why I feel the sudden launch into space on speed humps. I may buy one of Alteredegos rear bumpers with swing arm, as I feel the heavy wheel may hurt the rear door. I have not even driven offroad yet with the ZL-7 springs.