Tire pressure for 31s? Same width means same pressure?

[SSTJ]

Keep in mind; when we talk about lowering pressure for ride quality or for any other reason, we're only talking about a few pounds. It's very subjective and most would never notice the difference in comfort or tire wear. Think about how most people were never concerned with the difference between summer and winter air pressure until cars got TPMS.
IMO, you're overthinking it.

True, and I'm not losing sleep over it. I just want to know how to take care of my tires, not do anything stupid, and learn something along the way.

What's interesting is that I thought it was a simple rookie question, but here we are on page four of the discussion and it got a little heated along the way!

 

[SSTJ]

@SSTJ You never mentioned what width wheels you will be running with the upsized tires. As long as the rim is the same width as the wheels you are running the 30x9.5x15 tires on a chalk test would likely work for your needs and not run any risk of being under inflated. Typically that becomes an issue only when much wider tires are put on narrow wheels.

Here are a few articles concerning this subject. They also cover some cautionary points.

https://www.intercotire.com/using_chalk_method_determining_psi
https://fourwheeltrends.com/what-is-the-chalk-test-for-tire-pressure/
https://www.4wheelparts.com/the-dirt/how-to-find-the-right-tire-pressure-for-your-4x4-using-chalk/

Interesting, thanks. Yes, I had stumbled upon that Interco article earlier.

Well, I think that I'm going to stick with 29psi for my 30s, because that's what the door jamb recommends. For the 245/75/17s, which are being mounted on JK Moabs (7.5" wide, I think), I'll start with 28 because they're bigger and have a stiffer sidewall. I may play with the chalk test, but it sounds like the real way to make sure you aren't abusing your tires is to watch how it wears down over time.

 

[Srogers71]

I have my 31 10.5 15 x3s at 29lbs. No lift or any significant weight added to my 01. I Haven’t really investigated or tried any kind of Chalk test. But seems to be doing well. Ride is fine. I drive mine a lot on and off road. Been running some rougher trails and creeks etc. I would like to entertain a compressor and drop them even more depending on what I’m into. Still deliberating. I see these guys on you tube with all the crazy tire flex. It’s awesome. These are made for that. I wanna use them as designed.

 

[bobthetj03]

There are enough Jeepers on this forum who have cycled thru more than one set of tires, no matter what the size. Common wisdom would dictate a tire pressure that gives the best performance for our Jeeps. Personally, I'm on my 4 set of tires, all of which have seen 26-28 psi as the norm.

 

[freedom_in_4low]

2.2 bar is @ 32psi
View attachment 298172

Note the contact patch differences

do you have a link to this calculator? I'd like to play around with it...and see what it says if the corner weights are equal. I would fully expect the contact patch to be bigger with 100 pounds more weight on it.

I played around with the numbers in that link I posted above and found that at a given pressure, the wider tire had a smaller contact patch at low loads load, but grew more quickly than the narrower tire, reached a crossover point, and then had the larger patch at more load. These were some sort of racing tires on 13"ish wheels that I can't find any more data for, so I have to assume they were similar load ratings...I would love to find some radius vs load data for tires we actually use.

 

[reddvltj]

do you have a link to this calculator? I'd like to play around with it...and see what it says if the corner weights are equal. I would fully expect the contact patch to be bigger with 100 pounds more weight on it.

I played around with the numbers in that link I posted above and found that at a given pressure, the wider tire had a smaller contact patch at low loads load, but grew more quickly than the narrower tire, reached a crossover point, and then had the larger patch at more load. These were some sort of racing tires on 13"ish wheels that I can't find any more data for, so I have to assume they were similar load ratings...I would love to find some radius vs load data for tires we actually use.

View attachment 299381

Here ya go.

http://bndtechsource.ucoz.com/index/tire_data_calculator/0-20