Tire air pressure

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Pepperbelly

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Sep 3, 2023
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Fort Worth Texas
I just bought a used 2015 Unlimited Sport.
It came with Cooper STT mud tires, 285/70 17. The dealership aired the tires to 39psi and it rides like a buckboard.
I am thinking about airing down to 35psi or maybe 32.
What is a good pressure and what is the TPMS set for?
 
Snowbird Tom said:
Again, as explained in many threads about tire pressure, do a chalk test and adjust your tire pressure downward. I’m running 28psi in my 35s as my sweet spot. JScan will allow you to adjust the TPMS settings so the light comes on as appropriate.
Click to expand...
28psi feels amazing on my 35s as well…. Freeway and city driving
 
Snowbird Tom said:
Again, as explained in many threads about tire pressure, do a chalk test and adjust your tire pressure downward. I’m running 28psi in my 35s as my sweet spot. JScan will allow you to adjust the TPMS settings so the light comes on as appropriate.
Click to expand...
I will see about the chalk test. I think we used to do something similar with a bysiness caed. We parked so a lug of the tire was at the bottom and aired down until we could only slide the card under 1/8”. Is the chalk text about the same?
SocalRugger said:
28psi feels amazing on my 35s as well…. Freeway and city driving
Click to expand...
What is the oem setting psi for the TPMS? I don’t have a Jscan module yet.
 
Chalk test is where you run a line of chalk across the tread of the tire and then drive and see where it wears. You want an even wear. If it wears off in the center more than at the edges, you're still over inflated.

I don't recall what the factory settings are, but the placard on your door will tell you what the Jeep thinks it should be at. And for whatever reason shops and tire places always seem to want to put in 40 PSI regardless of what the placard says. J scan or other devices just allow you to run at the quote unquote proper pressure for your vehicle. Without the nanny light coming on
 
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JerryD said:
Chalk test is where you run a line of chalk across the tread of the tire and then drive and see where it wears. You want an even wear. If it wears off in the center more than at the edges, you're still over inflated.

I don't recall what the factory settings are, but the placard on your door will tell you what the Jeep thinks it should be at. And for whatever reason shops and tire places always seem to want to put in 40 PSI regardless of what the placard says. J scan or other devices just allow you to run at the quote unquote proper pressure for your vehicle. Without the nanny light coming on
Click to expand...
The dealer had the tires at 40psi whennI picked it up. It rode rough.
I just aired down to 32psi. My TPMS says 34psi. It’s better. I may try airing diwn to 30psi on my gauge and see if the nanny light comes on. I guess it really doesn’t matter if it’s on. It’s annoying but not a real problem.
I will be ordering a Jscan anyway.
 
Pepperbelly said:
I will see about the chalk test. I think we used to do something similar with a bysiness caed. We parked so a lug of the tire was at the bottom and aired down until we could only slide the card under 1/8”. Is the chalk text about the same?

What is the oem setting psi for the TPMS? I don’t have a Jscan module yet.
Click to expand...
The chalk test is a pretty useful tool. Draw a series of parallel lines across each tire. I've used anything from three to five lines. Then drive down the street, or in a big, mostly empty, parking lot for a couple of hundred yards at least. Then inspect the sets of lines on each of the tires. If the lines are gone from the central portion of the tread, but not from the edges, your pressure is too high. If the lines are missing from the edges of the tread but still noticeable in the centers, the pressure may be low. What you want to see is even removal of chalk across the entire tread width. The maker's recommended pressure is on the placard on the driver's side door or B-pillar. But . . . that pressure is for the factory issued tire size. My JKU Rubicon Hard Rock came with 255/75R17s, which are the same as 32.1 X 10R17s. When I bought it used, it was wearing the same size. I keep mine around 35 PSI. The TPMS doesn't complain until the pressure drops to about 32 PSI.
 
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