Tire pressures for 37s

BillArnett

New member
Of course, the door sticker that displays the recommended tire pressures is completely irrelevant when going to much bigger tires. So what pressure would you recommend for freeway driving? For easy trails? For heavy rock crawling?

I know there are supposed to be a couple of ways to figure this out. The easiest would be to check the tire manufacturer’s load vs pressure tables. But I’ve never been able to find them on the Net. And I’ve tried the method of putting a chalk mark on the tire and driving a bit to see which part wears off but I’ve never had much luck interpreting the results :-(

Also, have any of you succeeded in getting your JL’s computer set so that the TMPS warning comes on at a pressure more suitable for your larger tires? Supposedly the dealer can do this but they may be reluctant.
 

Onlyone

Member
Of course, the door sticker that displays the recommended tire pressures is completely irrelevant when going to much bigger tires. So what pressure would you recommend for freeway driving? For easy trails? For heavy rock crawling?

I know there are supposed to be a couple of ways to figure this out. The easiest would be to check the tire manufacturer’s load vs pressure tables. But I’ve never been able to find them on the Net. And I’ve tried the method of putting a chalk mark on the tire and driving a bit to see which part wears off but I’ve never had much luck interpreting the results :-(

Also, have any of you succeeded in getting your JL’s computer set so that the TMPS warning comes on at a pressure more suitable for your larger tires? Supposedly the dealer can do this but they may be reluctant.

I run about 28 in mine. It seems happy at that pressure.
 

unaseer

New member
I aired mine to 25 psi and didn't like the feel. They feel better with 30 psi. I'm running 37x12.5 17 Cooper STT Pros.
 

wayoflife

Administrator
Staff member
It really depends on the 37 as tread width and load range will make a big difference in how much air you'd want to run in them. Typically, around 30 psi or less is where you'd want to be for a nice ride and even wear. That being said, there currently is no means to turn off the TPMS warning light on the dash.
 

BillArnett

New member
I’ll be running 37x13.5 17 Cooper STT Pros, same as Jet Li. What pressures were you using on your trip to Moab?
 

wayoflife

Administrator
Staff member
What kind of mileage do you get with 37s?

We drove about a thousand miles out to Moab averaging about 70-80 MPH, crossed multiple mountain ranges, spent a week doing a lot of low range wheeling and then drove home again. According to our calibrated trip computer, we still managed to average 14.5 MPG. This is a HUGE improvement over our JK's.
 

JTCO

Meme King
We drove about a thousand miles out to Moab averaging about 70-80 MPH, crossed multiple mountain ranges, spent a week doing a lot of low range wheeling and then drove home again. According to our calibrated trip computer, we still managed to average 14.5 MPG. This is a HUGE improvement over our JK's.

That's damn good. My WJ (granted I carry a lot of shit) was getting 11-13 with 33s but with 35s, it's getting 9-10 mpg. 14.5 with 37s is very impressive IMO.
 

wayoflife

Administrator
Staff member
That's damn good. My WJ (granted I carry a lot of shit) was getting 11-13 with 33s but with 35s, it's getting 9-10 mpg. 14.5 with 37s is very impressive IMO.

I'm glad you mentioned it, I carry a ton of shit too and that includes a heavy ass welder, tools, fluids, etc. and we STILL got pretty decent MPG. :yup:
 

BillArnett

New member
To Moab, about 37 psi. Too high for my taste but it at least got the TPMS warning to stop coming on.

Wow, that's really high for those tires on a JL. You'll probably see very uneven tread wear. That might partially explain your really good mpg, though.

If you believe the hype from Z Automotive Technologies their Taser JL will let you reset the TMPS threshold. I'm hoping I can convince my dealer to do it for me.
 

BillArnett

New member
I did the calculation based on the load and inflation tables from Toyo (these tables are generic to all tires of a given size; Toyo just added a nice write up of how to use them):
https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf
The result is 25 psi for a JLUR running 37x13.5R17LT tires. Maybe a little more if you’re carrying a lot of gear; add 1 psi for every 69 lbs. But I suspect the recommended pressure that we’re starting with includes some load already.

So I’m going to start with 25 psi for normal driving and see how it goes. Higher pressures usually translate to slightly better fuel efficiency so that might be a worthwhile trade off for long trips though it will cause uneven tire wear and hence shorter tire life. But the cost of a set of these tires will buy a lot of gas so I doubt it would be worth it. More important will be what the ride/handling is like at different pressures. That will take some experimentation and be highly subjective.

Off road pressure is not so easy. I guess I’ll start with about 1/2 of the street pressure. Sound reasonable?
 

JTCO

Meme King
An easy way to determine a good on-road tire pressure is by using sidewalk chalk and chalk an entire 6 inch area across the tread. Reverse the Jeep about 50 feet and then go forward again to the spot you started. Get out and look at the chalk that's remaining. It should be evenly worn off or be about the same shade of color.

If the chalk is still more visible in the center, your tire is under-inflated and you need to add more air and check again.
If the chalk is still more visible on the outer edges, your tire is over-inflated and you need to remove air and check again. On mud tires, the very outside of the outer lugs on both sides will probably still have some chalk, it's hard to get the very edge to wear with the center on aggressive mud terrain tires.
If the chalk is still more visible on ONE edge only, you likely have some kind of alignment problem.
 

Amric

New member
I used the tire temperature method and get even tire temperatures inside to outside tread at 26 psi when running 37” KO2s.
 

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