Good info, and this comes up all the time on the RV.net forums.

Take my motorcoach for example. The rear axle weighs 17,800 lbs., the front 9,600 lbs. Just because the Toyo M120z tires which are mounted on 22.5'' wheels say 120 PSI max doesn't mean they need to be blown up to that amount. According to Toyo's charts for the tire's particular size, the rear tires (the PSI pressures per weight are different if they're dual) run 100 PSI. The front axle tires run 105 PSI. That's a helluva lot less than the 120 PSI max. If they were maxed, they would wear out in the tread center.

Commercial vehicles which can include heavy RV's, always need to be weighed and a tire manufacturer's chart consulted before just guessing as what to put in a tire. It shouldn't be any different for our Jeeps. Especially the Commander for that matter, as it's a heavy rig. My XK weighs a bit more then our Ford Expedition in fact, despite being a smaller vehicle. An XK is a stiff as a Tonka Toy for a reason. (Very little body twist)