I know some of you guys are running LT tires. My zj calls for 36psi but that's with a P tire. I got some Michelin LT 225 16's. What do you guys put your pressure at? I figure 36lbs isn't enough since its not a P tire anymore I'm putting them on in a few hrs will post pics..
The LT tires are going to ride a bit rougher, but with the same size tire, it really shouldn't need all that much more pressure. Don't fill them up to what some guy on here tells you to, and especially dont fill them up to the "max psi" pressure, instead, fill them using the chalk method.
It involves rubbing a line of chalk over the tire tread, and driving a few revolutions, and checking the wear on the chalk line. You want the whole thing to wear evenly. If you have too much wear to the Inside and less on the shoulders, you're overinflated. If the shoulders are wearing more than the center, you're under inflated. It may take some playing with it to get it right, but your tires (and your jeeps ride) will thank you later.
95 Limited Chargold ZJ 5.2L -5.5" lift (IRO, Ironman, and RC parts), 33" BFG M/T's, 15x8 procomp crawlers, 242 swap, 2 12" subs, 1000w amp, cherry bomb, full skid package, Kevins rear stealth bumper clone w 3/4" D rings, Rlcwelding front bumper w 3/8" D rings, XRC-8, front tow hooks, 2 daylighter fairlead lights, 2 daylighter windsheild lights, 2 55w driving lights, OBA, Cobra 18 CB, dual 4' whips, RC disconnects, smittybuilt jack, optima yellowtop.
My guess is that you will end up in the low 30s to get even wear unless you are carrying a heavy load. Look at the load rating of the tire. If it is higher than the tire you are taking off, the correct pressure will be lower than 36 psi. The stiffer sidewall will not flex as much as the "P" tire.
Air is what holds the vehicle up. The tire just holds air in. When you see tires rated for higher pressure, that doesn't mean they need higher pressure. It means in order to support the higher weight rating on the side of the tire, you need more pressure, and this tire will contain that pressure safely.
So unless the weight of your truck increased by 1000 lbs with LT tires, you're always safe at the old/lower pressure specified by the lighter tire.
The chalk test is a good way to verify, but so is playing with pressures to find what you like, then observing tire wear closely to see if you can live with that wear pattern. Over the years I've found my preference is typically lower than the chalk test. Possibly because of pressure rise with heat, or maybe just because.
I find it hard to believe that your tires will wear evenly at 40 psi supporting about 1100# per tire. What is the load capacity of the new tires? What Load Range are they? There are performance tables that tell what pressure to carry on a particular tire based on its capacity and the load it is carrying. Too high a pressure in an LT tire can still show a good chalk pattern, but will give a harsh ride. I've used performance tables on a lot of tires, but most are on larger sizes and all of the tires have worn correctly.
edit: Look up Load/Inflation Tables. You'll have to search a little to find one that will cover your tire, but using those tables I have run OEM Avalanche tires over 80,000 miles with the psi between 28 & 36 depending on the load. The chalk test will get you close, but the load/inflation table is put out by the tire makers and they are correct. To do it right, you have to know what the tire is carrying.
You may be reading too much into the "LT" rating and what the max pressure says on the side of the tire. I run Michelin M/S LTX tires on all 4 of our Jeeps, keep them inflated between 33-34psi, and the tread wears evenly. Just went out and looked at the LTX tires on my 96 ZJ (235/75R15) and it says I can put 60psi in them, the Michelin site says up to 44psi max, and there's no way I'd run more than 35psi in mine.
Know every Jeep/tire is a little different, and you have the 5.2 vs 4.0, but believe I'd be checking the middle tread wear fairly soon if running 38-40psi.
I just can't live with the ride of my E Load tires at those pressures. It's terrible enough at 32.[/QUOTE]
When I had 33" KM2s on my ZJ, which were an LT load range E, I ran them at 28-30 psi for ride and even wear. (the tire said 80 psi for max load) The 35s I have now are LT LR D and I run them at 26-28 psi for even wear and good ride. (my ZJ weighs 5300#s with all the armor, bumpers and suspension) Another rule of thumb that is close, is that if the load on the tire is 75% of its max rating, you can run 75% of its max pressure. That formula happens to match the load/inflation chart the Michelin puts out for the 275/80x22.5 load range G tires on my motorhome. It also works for the tires on my 3/4 ton pickup.
The tire information is available, but if the OP wants to run 40 psi in his tires, it won't hurt a thing accept his ride and how they wear.
Yeah, 40psi is too much pressure for the Michelin LTX. I've had 2 replacement sets, currently running 4 fairly new LTX sets on my 96 ZJ, 93 XJ, wife's 2000 TJ, and son's 96 XJ. The couple tire companies I've used fill them to 35psi and say that's the LTX spec for all of them. Like I said I keep them filled between 33-34psi but if going on a long trip I'll go to 35psi for better gas mileage.