What PSI to run in 31" MTs?

With a slightly larger than stock tire, the psi should be somewhat lower than what's on the door jamb.

RangerX said:

With a slightly larger than stock tire, the psi should be somewhat lower than what's on the door jamb.

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So under 35psi? (35 is what's recommended if I recall correctly). That seems low to me but why should I be running it lower if I use a larger tire? Is it because of the weight distribution and added weight/width of the larger tires?

Well until recently, anything under 45 seemed low to you, right? It's just a number. What you want is for the full width of the tire to make contact with the road. Whatever pressure that it takes to accomplish that is the right pressure.
A street bicycle with a 1" wide tire runs 90-110 psi, but a mountain bike runs 45-60, why?
I run 35s on my Ranger. BFG KM2s, the real aggressive tread. I run them at 27 front and 24 rear, because that's what I determined gets full contact. I have over 40,000 on them and they are wearing evenly. With the tread that's left, I should get another 10,000. I couldn't do that with too high of psi.
Try 35. Drive through a puddle and then look at your tire tracks on the dry pavement. You'll see whether you're getting shoulder to shoulder contact, and can adjust accordingly. Up, down, whatever it takes. It's just a number.

Well said above. I run 26 psi in my 35s and drive 70 mph on the highway regularly. I would suggest 32-35 psi at most for your 31s.

Thanks guys. I guess for some reason my brain was wired for the "more is better" philosophy. I guess that doesn't apply to everything. I do want to maximize the amount of even wear on my tires. Thanks again guys and I'll be airing them down directly.

:JP:

That's the Jurassic Park Ex icon. First time I noticed it. Nice.

I am running about 42 psi in my 31x10.5 15 BFG ATs and I get full contact , but every tire is different so what I do is air them up to about 45 then place a framing square across the tread and air down till its square , sounds silly but it works

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RangerX said:

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Aired down to 35psi a few days ago. Been riding around in the rain and ice/snow and the truck definitely feels like it's gripping the road more than before. I think I'm gonna leave it at 35.

Thanks guys.

Sounds good, glad it works out.

Yep. I was thinking it would feel too spongy for my liking. However, 35 psi feels pretty good.

35psi is normal and give better tire contact for traction.

The "best" pressure to run in a particular tire size depends a lot on the vehicle and the load on the axle the tires are on.

Whatever pressures give even wear across the tread is the "correct" pressure to run a tire at.

There's really a range of pressure you can be within and still get even wear, so the low end gives a softer sidewall and smoother ride, the high end gives a firmer sidewall and stiffer ride.

45-50psi is probably too high for daily driving, since that's close to the maximum pressure, which is what you would use if the tire was fully loaded, such as stuffing the vehicle to max capacity or towing a trailer.

35psi should be a much better pressure, but keep an eye on the tread. Things like cornering and alignment also affect tire wear, and just keeping a tire inflated a few more psi can be the difference between one that wears on one shoulder due to alignment/handling and one that wears evenly.

It should also be noted that the front and rear tire pressures don't always have to be the same. With the weight of the engine, transmisson, air conditioning, etc. in front, even with 200+ lbs of gear in the back, SUVs like the Explorer can be still be front-heavy, so sometimes running the front a psi or two more than the rear can give even wear all around.

It really is trial and error, even with the factory size, but especially when running tires with different characteristics than what it came with (light truck, off-road, high performance, extra load, etc.). The factory tire pressure sticker is a good minimum to go by, but you can get longer tire life, better mileage, and even tire wear by experimenting with pressures and finding what works best for a particular tire in a particular size for a particular vehicle loaded a certain way.