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Highway pressure for 37's on a 392XR?

stumblinhorse

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That is not the tire my 2021 392XR came with from the factory. Mine came with 35x12.5R17 113/110S KO2. Perhaps the 2022 models have a different tire now?
That tire is not on the BFG site…. I edited once I remembered you have an XR. So they are prolly mopar only KO2s.
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richk225

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My 2021 392 Rubicon XR came with BFG KO2`s 315/70/17 C range and I had BFG KO2 37x12.50x17`s put on before I picked it up. The BFG KO2 35x12.50 x17 is a C range tire
The 3 BFG KO2 tires size 315/70/17 all have a 8"-11" rim recommendation, one is for a Jeep and has a S speed rating, one is for the Ford Raptor and has a T rating, and one has a E range and is discontinued according to BFG. The 35x12.50x17 has a E range and a R speed rating and has a recommended rim size of 8.5"-11"

https://www.bfgoodrichtires.com/auto/tires/all-terrain-t-a-ko2?tyreSize=17#sizes

Jeep Wrangler JL Highway pressure for 37's on a 392XR? 062.JPG


Jeep Wrangler JL Highway pressure for 37's on a 392XR? 064.JPG
 
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Chris-AZ

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My 2021 392XR arrived at dealer on 35’s (not 315’s) in 3rd week of December and I picked it up 1st week of January. Maybe they ran out of 315’s? AFAIK, the 35’s are supposed to be on a 8.5” rim. But I’m not going to dismount to measure.
 

stumblinhorse

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My 2021 392XR arrived at dealer on 35’s (not 315’s) in 3rd week of December and I picked it up 1st week of January. Maybe they ran out of 315’s? AFAIK, the 35’s are supposed to be on a 8.5” rim. But I’m not going to dismount to measure.
Agree, most 35s the manufacturer specs 8.5” rims. But not the 315 KO2s. So for sure XR rims are only 8“. So wonder how Jeep can explain having the 35s out in the wild on XR rims.
 

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1996cc

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That is cool that you can still drive like that at 90 years old LOL
That`s more like fly a way speed!
Are you running true bead locks?
Yes. KMC XD 231’s
 

Whaler27

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I agree with you, when I picked up my 392 XR it had 37 psi in all 4 tires and after a hour of driving this went up to 40 psi. I have always run nitrogen in my tires to combat this problem, one benefit of Costco. There are other ways to purchase it and it does make the tire run cooler and not suffer as much air loss due to being a gas that is more dense than air
Nitrogen doesn’t combat that problem.

Nitrogen, like all gasses, responds to temperature.

The air we breathe is approximately 80% nitrogen anyway, so any effect from swapping to 100% nitrogen has a bigger impact on your wallet than your tire behavior.
 

richk225

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Nitrogen doesn’t combat that problem.

Nitrogen, like all gasses, responds to temperature.

The air we breathe is approximately 80% nitrogen anyway, so any effect from swapping to 100% nitrogen has a bigger impact on your wallet than your tire behavior.
Thanks for the info, much appreciated
 

veddersbetter

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My 2021 392XR arrived at dealer on 35’s (not 315’s) in 3rd week of December and I picked it up 1st week of January. Maybe they ran out of 315’s? AFAIK, the 35’s are supposed to be on a 8.5” rim. But I’m not going to dismount to measure.
Interesting .. mine was built around the last day of 21 production.. 12/18 or 12/21 I think.. and arrived second week in January.. mine are 315's. I assumed they all were
 

Petes_392

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My 2021 392XR arrived at dealer on 35’s (not 315’s) in 3rd week of December and I picked it up 1st week of January. Maybe they ran out of 315’s? AFAIK, the 35’s are supposed to be on a 8.5” rim. But I’m not going to dismount to measure.
Can you post a picture of the sidewall showing the tire size..??
 

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Isn’t 35 vs 315 at most only like a 0.5” difference? Sounds like similar/same tires to me
 

richk225

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Isn’t 35 vs 315 at most only like a 0.5” difference? Sounds like similar/same tires to me
BFGOODRICH® ALL-TERRAIN T/A KO2 - 35X12.50R17/E 121R RWL

35X12.5R17 121R RWL
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Mileage Warranty50,000
Section Width on Measuring Rim Width12.50" on 10.00"
Overall Diameter34.5
Max Load, Single (LB @ PSI)3195 @ 65
Revs/MI602
Tire Weight66.36
Rim Width Range (Min/Max)8.50-11.00
Tread Depth (in 32nds)151
Specifications
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BFGOODRICH® ALL-TERRAIN T/A KO2 - LT315/70R17/C 113S RBL
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Section Width on Measuring Rim Width
12.70" on 9.50"
Overall Diameter
34.4
Max Load, Single (LB @ PSI)
2535 @ 45
Revs/MI
604
Tire Weight
63.40
Rim Width Range (Min/Max)
8.00-11.00
Tread Depth (in 32nds)
151
Specifications
3PMSF
M+S

BFGOODRICH® ALL TERRAIN T/A KO2 - 315/70R17 121S RBL
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MSPN
08806
Mileage Warranty
50,000
Section Width on Measuring Rim Width
12.70" on 9.50"
Overall Diameter
34.4
Max Load, Single (LB @ PSI)
3195 @ 65
Revs/MI
604
Tire Weight
65.21
Rim Width Range (Min/Max)
8.00-11.00
Tread Depth (in 32nds)
151
Specifications
3PMSF
M+S

BFGOODRICH® ALL-TERRAIN T/A KO2 - LT315/70R17/C 113T RBL
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MSPN
07361
Mileage Warranty
50,000
Section Width on Measuring Rim Width
12.70" on 9.50"
Overall Diameter
34.4
Max Load, Single (LB @ PSI)
2535 @ 45
Revs/MI
604
Tire Weight
63.67
Rim Width Range (Min/Max)
8.00-11.00
Tread Depth (in 32nds)
151
Specifications
3PMSF
M+S
 

JMP

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Nitrogen doesn’t combat that problem.

Nitrogen, like all gasses, responds to temperature.

The air we breathe is approximately 80% nitrogen anyway, so any effect from swapping to 100% nitrogen has a bigger impact on your wallet than your tire behavior.

“"But air is 80% nitrogen," I pointed out, "What's the advantage of using pure nitrogen?" Peter explained that nitrogen is used in aircraft tires to reduce the effect of temperature fluctuations on pressure.

I didn't press him on the issue, but I remained puzzled. Under everyday conditions, the gas in a tire should behave like an ideal gas—that is, its pressure should be proportional to its temperature regardless of its molecular composition. Curious, I looked into the matter.

Aircraft tires indeed are filled with nitrogen to mitigate temperature fluctuations, but not because nitrogen has any special heat-absorbing qualities. Rather, it's the presence of water that makes standard, commercially available compressed air a poor, even dangerous choice for aircraft tires.

At low temperatures, such as a plane might encounter at Chicago's O'Hare airport in midwinter, the water in an air-filled tire exists as liquid droplets. But if that plane had to land and brake suddenly, heat from the screeching tires would vaporize the droplets, adding an extra pressure-exerting component to the gas in the tires.

The sudden increase in pressure from the water vapor can be fatal. On 31 March 1986, a tire on Mexicana Flight 940 was mistakenly filled with air, not nitrogen. Fifteen minutes after takeoff from Mexico City, an overheated landing gear brake caused the tire to explode. The resulting crash killed all 167 passengers and crew.

Pure nitrogen has other advantages over air besides its dryness. When tires get very hot, oxygen, the second most abundant component of air, can react with volatile chemicals in the rubber and cause an explosion. Even at lower, everyday temperatures, oxygen reacts with rubber, weakening it.

So will I refill my tires with nitrogen? Not if it costs more than a few dollars. Having owned the same car for 18 years, I know that worn treads will prompt me to replace the tires long before oxidation sets in.”
 

C.Sco

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In my 4xe on 37's I usually inflate to 32psi cold. Normally they'll warm up and get to about 35-36 on a typical day, and on a hot day with a lot of driving they'll get themselves up to 39-40 sometimes.

So 32 psi cold seems like the sweet spot for me.
 

Whaler27

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“"But air is 80% nitrogen," I pointed out, "What's the advantage of using pure nitrogen?" Peter explained that nitrogen is used in aircraft tires to reduce the effect of temperature fluctuations on pressure.

I didn't press him on the issue, but I remained puzzled. Under everyday conditions, the gas in a tire should behave like an ideal gas—that is, its pressure should be proportional to its temperature regardless of its molecular composition. Curious, I looked into the matter.

Aircraft tires indeed are filled with nitrogen to mitigate temperature fluctuations, but not because nitrogen has any special heat-absorbing qualities. Rather, it's the presence of water that makes standard, commercially available compressed air a poor, even dangerous choice for aircraft tires.

At low temperatures, such as a plane might encounter at Chicago's O'Hare airport in midwinter, the water in an air-filled tire exists as liquid droplets. But if that plane had to land and brake suddenly, heat from the screeching tires would vaporize the droplets, adding an extra pressure-exerting component to the gas in the tires.

The sudden increase in pressure from the water vapor can be fatal. On 31 March 1986, a tire on Mexicana Flight 940 was mistakenly filled with air, not nitrogen. Fifteen minutes after takeoff from Mexico City, an overheated landing gear brake caused the tire to explode. The resulting crash killed all 167 passengers and crew.

Pure nitrogen has other advantages over air besides its dryness. When tires get very hot, oxygen, the second most abundant component of air, can react with volatile chemicals in the rubber and cause an explosion. Even at lower, everyday temperatures, oxygen reacts with rubber, weakening it.

So will I refill my tires with nitrogen? Not if it costs more than a few dollars. Having owned the same car for 18 years, I know that worn treads will prompt me to replace the tires long before oxidation sets in.”
Yup, although Chicago in the winter never gets as cold as the air at commercial flight altitudes. It can be 40 degrees below zero up there when it’s 80 degrees on the ground below.

For automotive uses, It’s probably a good idea to use nitrogen if you expect to keep your tires more than 60 or 70 years. For the rest of us, free air works pretty well.
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