It's mostly a matter of personal preference. 33 or so is recommended by manufacturer on manufacturer's recommended tire size. I would say anywhere from 30-40 would be fine on most tires for highway, just match them up. The lower the pressure the more soft the ride. As a downfall it can make turns feel 'mushy' as one person said above and lowers your mileage. Higher pressure will give you better fuel economy and feel more solid in normal turning situations, but you will feel more rocks and bumps than before.

Going really low can have you riding on your side wall which is bad news, it's not as thick on the sides, by far, than on the tire's tread, while too high of a pressure can wear the tread down in the very center and cause premature wear. A lot of people just look at their tires with a quick walk around from a side view and think there is plenty of tread left, but we would have some come in for a balance and there is steel belt showing in the center.

Provided your vehicle is properly aligned keep an eye on your tires as you use them and watch for any strange wear patterns, you should adjust your pressure accordingly, you want the entirety of the tires tread on the ground as you are driving.

If you drive in the city and rarely on highway you may want to choose a slightly higher pressure say 35ish. While if you are on highway and commute and hour everyday maybe 32ish. As the tires get hot the air expands and raises the pressure. The number on your tire of course is the maximum cold pressure however. So, provided your tire is in good condition and not weather cracked or excessively worn putting the max pressure and driving for a long while won't heat up and blow your tire, but having a lot of pressure is usually for load bearing tires or for use on trailers and use daily would probably where it thin in the middle.

Off-road however, is probably more along the lines of personal preference and what you are doing off road. Mudding, Crawling, duning, it's really on a per application basis and it's something you would have to get the feel for with practice.

 

I aired down to 40 p.s.i. The ride is about the same. Next time I gas up, I'm going to check the mileage.

In the past I always ran 32 p.s.i. in nearly every car or truck I owned, except a 3/4-ton '66 Dodge Power Wagon I had, in which I ran 28 p.s.i. I lived up in the Blue mountains in Washington State and spent a lot of time on logging roads and out in logged-over clear-cut areas cutting firewood out of the slash piles.

Off road, I'd go down to about 15 p.s.i. in my Cherokee, provided I had access to an air compressor. Airing down costs gas money on the ride home, and I don't normally go anywhere down here in South Texas that really requires all that much traction. A little mud, maybe. No big rocks or any of that white knuckle stuff like they depict in off-road magazines.

 

I'm surprised nobody with aftermarket tires uses the chalk test. Load ranges for all tires vary and the chalk test is the best way to ensure proper contact patch and tire wear.

 

the chalk method works to a degree.

with off road tires, the sidewalls are much thicker, so there could be a variance of 5psi or more that will go totally unnoticed on the chalk pattern. but it is a very good start, then add or remove pressure to get the right feel.

40-50psi is absurd. but if you really think you need that much air, who am i to say.

 

I agree.

My buddy at Discount Tire always suggests starting with the pressures that are on the door jamb and then go up or down 2 PSI at a time. That combined with a chalk test should get you real close.

 

I run my 35x12.50's at 18 psi on the road and bout 10 off. No bead locks either. The xj spent weigh enuf to run more than 25-30 psi in big tires. I'm bout to do h1's and I'll run them at 15 every day on the street.

 

Thank you for all the input. I like seeing the responses that are generated. I asked simply because I has heard so many different set ups being run. I agree with about 90% of your answerers. And will consider lowering my pressure more next time we have really snowy roads... Assuming that we actually get some snow this winter.
Any stories of tire disasters? Those are always interesting...

 

All good points; chalk test, even pressure, etc. Good discussion. I'll just add that each tire is different. Bias ply act much differently than radials, for instance, so I would play around with it. Try different pressures, see how it acts.

When I first got my LTB's which are bias, I aired down to 12psi offroad which did fine, except in snow. I tried 10, then 8psi and it made a huge difference.
I don't run much more than 20 in them on the road, but it doesn't see much pavement.

But don't be afraid of changing it. It's pretty easy to put back in if you don't like it.

 

Filled up yesterday (to the the of $44.11 for 12.46 gallons), and I had driven 185.4 miles, in city traffic and freeway. With the tires at 40 psi, I got 14.87 mpg. ??? That's better than I did last fillup with the tires at 50 psi. Grrr! My theory about airing up the tires doesn't seem to be holding up. I'll try again.