This is what I was going to add and I seen it had all ready been mentioned. It's the best way. It depends on the weight of the vehicle, a big F250 diesel might take 50 psi to get a good chalk test. With the same tires on a jeep it might take 30 psi. My 35 MT MTZ's on my 2 door took 30 psi to get a even wear of chalk across the tread. I had 35K on my MT's when I traded in my 2 door, between the tire pressure and doing a 5 tire rotation and balance every 6K my MT's still had 60 to 70% on them.

 

28 most of the time on my Toyos. 35 on long highways drives. 15 on the trails.

 

You have comfort, tire wear and safty to consider. Very large tires are built to run on very heavy rigs. Even a fat JKU at 5500lbs is light compared to a 3/4 or 1 ton truck.

So you need enough to carry the load, not roll over the tread or make too much heat. Also so the tire makes a good contact patch and finally no so much that you get a concussion or bounce like a super ball when you hit a bump.

I run 26psi in 37" Iroks on 16" wheels in the D load range on the street and 8psi off road. BTW my JKU weighs in at 5200lbs with gear and a full tank.

Experiment until you strike a balance. I would start at 28PSI.

 

27.5 35x12.5 KM2s .....haven't done a chalk test though. Probably should before long....I put a lot of highway miles on them.

 

Again, too general of an answer. My Rubi unlimited has lots of mods making it a bit overweight (by a "bit" I mean "a lot"). The BFG KM2 tire seems to like high pressure. I run 35 on the freeway and it's a nice ride - no "shock waves" at all. I've been to 38 just to see the difference and then it's like riding a basket ball down the highway. The chalk test works for me between 28 and 35 PSI - hard to tell the difference.

If you are running a Load Range E bias-ply tire on a 2-door that has been stripped to the bone, 20 might be too much for a good ride. If you have a Load Range C radial on an unlimited with built bumpers, winch, full-sized spare, tools, spare parts, skids, 20 gallons of water, 10 gallons of extra gas, propane tank and grill, a couple of big dogs, roof rack, camping gear, towing a 3500# trailer, wife, kids, and a spare toothpick, 35 might not be enough. Of course with that much crap on/behind the Jeep I'd worry a lot more about other things other than the tires! I've seen it done, though.

The answer is simple. Do what works best for your situation. If 35 PSI is too hard, don't air up to 35. However, my 2 cents is it's better to be slightly over-inflated on the freeway than under-inflated. Excess heat buildup when under-inflated might have disastrous consequences.

 

new 35s were installed tonight. they had 38 lbs in them. waaaaaay too bouncy. i put them down to 30 and they feel really nice now.

 

.....

 

I run 28-30 in my grapplers also.

 

Same here 26-28. Nice ride

 

That's a good place to start and a lot of opinions posted without mentioning what tires are being run.

Look at your placard data for inflation rate of the stock tires. Get the service description number of the OEM tires. Use an ETRTO chart to see how much weight the stock tires were supporting at the given inflation rate. Look up the service description number of the replacement tires. Use the ETRTO chart to find out at what inflation rate they support the same weight as the OEM tires. Inflate tires to given inflation rate. Do a chalk test and hone to desired comfort/economy level.

There is no magic bullet and soliciting opinions without details and getting responses in kind is a hapless journey.