Highway pressure for 37's on a 392XR?

[Chris-AZ]

I have a 392 XR, came with 35's but I put 37's on (BFG KM3) stock XR wheels (which I think are 8.5" wide with 4.5" backspace). What would be the ideal tire pressure for street/highway? I have a Tazer to reset the target.

 

[richk225]

I have a 2021 392 Rubicon XR that I had 37" BFG KO2`s put on before I picked it up, I also had a 2021 392 with 35" BFG KO2`s. I believe the XR is an 8' wide wheel
Also a Ford Raptor with the same 35'`s on it
There is a lot of debate on what pressure to run, you can do a tire chalk test, follow what is on the vehicle mfg sticker.
I personally run 34 psi in the front and 32 psi in the rear and it suites me just fine. You can listen to what people have run, and it depends if you are driving a empty Jeep with 2 people or a loaded up one with 4 people and gear along with what accessories you have added to yours. You can always air up when loaded up and air down when your just cruising the highway. My Raptor was a whole different story, the ass end would skip left or right at highway speed (65 plus) when it hit a gap in the road or expansion joint on a bridge. I tried all different tire pressures and nothing worked and after reading up on the issue on the Raptor forums the rear leaf springs were the culprit. I had changed them and never had an issue at any tire pressure, Raptors are now using coil springs in the rear so that should solve that problem

 

[stumblinhorse]

a lot of variables in tire psi. So try a psi and adjust. Remember 1 psi increase per 10 degrees increase in temp of air in the tire, on average. So I set to 30psi 1st thing in the morning when I check. That might get to 35-36 in The heat of the day on the hiway. It is cold here in the morning in my garage. You might be outside and in the sun in the AM when you check. I never want more than 35 psi in my tires at their hottest, so I adjust based upon highest psi.

 

[guarnibl]

I have mine (KM3) 37" set to 32 psi cold.

 

[richk225]

a lot of variables in tire psi. So try a psi and adjust. Remember 1 psi increase per 10 degrees increase in temp of air in the tire, on average. So I set to 30psi 1st thing in the morning when I check. That might get to 35-36 in The heat of the day on the hiway. It is cold here in the morning in my garage. You might be outside and in the sun in the AM when you check. I never want more than 35 psi in my tires at their hottest, so I adjust based upon highest psi.

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

 

[Terpsmandan]

I have a JLURD with a Mopar lift and 37" KO2's I started at 35 and then to 32 psi but when I ran over a puddle the tire track that it left was not a full tread. I am running 30psi now and thinking that might be still too much. I am going to chalk the tires soon the check it out.

 

[guarnibl]

I have a JLURD with a Mopar lift and 37" KO2's I started at 35 and then to 32 psi but when I ran over a puddle the tire track that it left was not a full tread. I am running 30psi now and thinking that might be still too much. I am going to chalk the tires soon the check it out.

Yeah, always should chalk test. For me, 32 psi was the right number on my KM3's. My KO2's I run at 27. Could just be weight differences or something, not sure. Both are D rated. 37" KO2s on my JTRD, 37" KM3's on my 392XR.

or I'm terrible at chalk testing

 

[richk225]

Yeah, always should chalk test. For me, 32 psi was the right number on my KM3's. My KO2's I run at 27. Could just be weight differences or something, not sure. Both are D rated. 37" KO2s on my JTRD, 37" KM3's on my 392XR.

or I'm terrible at chalk testing

The best part about a chalk test back in the day was you got to throw the eraser at someone.
I have seen guys use a spray bottle of water to lightly wet the tread down and then give it a roll over something flat, I have used a piece of plywood when I was not at my garage, but you are 100% correct in that every Jeep is set up differently and tire pressure is just part of the equation. My neighbor bought a GMC pick up and was running 75 psi in the tires, I swear you would loose a filling if you rode in that truck, he did not understand how to read the sidewall and just went to the max

 

[guarnibl]

The best part about a chalk test back in the day was you got to throw the eraser at someone.
I have seen guys use a spray bottle of water to lightly wet the tread down and then give it a roll over something flat, I have used a piece of plywood when I was not at my garage, but you are 100% correct in that every Jeep is set up differently and tire pressure is just part of the equation. My neighbor bought a GMC pick up and was running 75 psi in the tires, I swear you would loose a filling if you rode in that truck, he did not understand how to read the sidewall and just went to the max

Yeah my 3500 HD SRW came filled to something stupid like 90. I mean I know for sure when you're towing you want more pressure and everything, but damn.

 

[MSparks909]

Running 28-30psi cold in my 37s currently

 

[Chris-AZ]

Thanks for all the feedback guys, appreciate it.

 

[Covet]

XR 35s, 300 miles in, dealer set them at 42. Been averaging 17 and some change mpg highway, uphill and downhill. Waiting for the temp to get to a more regular # then going to play with the psi

 

[MSparks909]

XR 35s, 300 miles in, dealer set them at 42. Been averaging 17 and some change mpg highway, uphill and downhill. Waiting for the temp to get to a more regular # then going to play with the psi

Lower it to 32-36 tops. It’ll ride smoother.

 

[richk225]

The one thing I forgot to ask you is, what motor is in your XR?

 

[Dyolfknip74]

The one thing I forgot to ask you is, what motor is in your XR?

Read the thread title again.

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