Proper air pressure for 315/70/17’s

Cruuzer

New member
I have some C range 315’s - currently they are at 42PSI, and its too much (flighty) I’m thinking 35 PSi is better, but curious what others are running?
 

wayoflife

Administrator
Staff member
I have some C range 315’s - currently they are at 42PSI, and its too much (flighty) I’m thinking 35 PSi is better, but curious what others are running?

Assuming you're okay with the TPMS warning light coming on or that you have a Tazer JL, I personally would run them closer to 30 psi. A chalk test would verify what you'd really want them at though.
 

Cruuzer

New member
Assuming you're okay with the TPMS warning light coming on or that you have a Tazer JL, I personally would run them closer to 30 psi. A chalk test would verify what you'd really want them at though.

Thanks

I just got my Tazer in the mail (thanks to WOL for the discount) so i can play with the TPMS settings, I’m going to try 32, do the chalk test and go from there, thanks again for the feedback
 

Cruuzer

New member
FYI for the 315’s at load range C, 32psi gives a great ride and it lost the “flighty” feeling it had before.

Although, it still doesn’t steer as well as my JK on 37’s with the EVO steering flip, its much better.

Much of this is personal preference I’m sure, just wanted to share for other out there.
 

SNACK_PACK

New member
Assuming you're okay with the TPMS warning light coming on or that you have a Tazer JL, I personally would run them closer to 30 psi. A chalk test would verify what you'd really want them at though.

Ultimately the BEST way to figure this out is a chalk test.
 

JTCO

Meme King
A chalk test would verify what you'd really want them at though.

Ultimately the BEST way to figure this out is a chalk test.

do the chalk test and go from there

Chalk test indeed is the most accurate way to determine proper tire pressure, especially in a heavy Jeep with gear and tools.

For anyone reading who isn't familiar with it, a chalk test is easy. Grab some sidewalk chalk, and mark about 6-8 inches of the tire.

IMG_20180517_165818_413.jpg

Drive the Jeep backwards about 50 feet, then go forward again to the starting point. Get out and take a look.

IMG_20180517_165947_643.jpg

The pattern above is nearly perfect.The chalk is worn evenly. This is a 35" tire with about 31 psi. On a mud tire, the very edges of the outer lugs will still show some untouched chalk and nothing can be done about it. They'll eventually wear with the center over time. All terrains and finer treads should wear all the way across evenly.

If the center shows fresh chalk, then the tire is underinflated. If the center shows worn chalk but the rest of the tread doesn't, then the tire is overinflated. If just one edge is worn, there is an alignment problem.
 

BillArnett

New member
Chalk test indeed is the most accurate way to determine proper tire pressure...

I tried that yesterday. I inflated each of my 37x13.5 STT Pro tires to a different pressure: 20, 22, 25, and 30. The one at 30 was clearly overinflated. But I couldn't tell the difference between the others. So I'm sticking with 25 which is close to the 24.8 that I calculated from the load tables.
 

JTCO

Meme King
I tried that yesterday. I inflated each of my 37x13.5 STT Pro tires to a different pressure: 20, 22, 25, and 30. The one at 30 was clearly overinflated. But I couldn't tell the difference between the others. So I'm sticking with 25 which is close to the 24.8 that I calculated from the load tables.

Truthfully I've never checked all 4 tires at the same time. And obviously weight and temperature plays a role. Were you on flat pavement when you did the test? Weird that you got 4 different readings.
 

BillArnett

New member
I tried that yesterday. I inflated each of my 37x13.5 STT Pro tires to a different pressure: 20, 22, 25, and 30. The one at 30 was clearly overinflated. But I couldn't tell the difference between the others. So I'm sticking with 25 which is close to the 24.8 that I calculated from the load tables.

Truthfully I've never checked all 4 tires at the same time. And obviously weight and temperature plays a role. Were you on flat pavement when you did the test? Weird that you got 4 different readings.

Not quite flat, just up and back on my driveway (part of which you see in my avatar).
 

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