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Old 04-22-2010, 03:04 PM   #1
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(potentially dumb) question about tire pressure

As far as I am aware, the data plate inside the driver's side door tells me the proper tire pressure for my tires - if they are tires of the size the vehicle was originally equipped with. The tire pressure number on the tire itself is the maximum pressure.

Is that correct?

If so, how would I determine correct tire pressure if my vehicle now has different tires? My Jeep originally came from the factory with 30x9.50 tires on 15" rims, and now has 31x10.50 tires on 15" rims. How would I determine proper / best tire pressure?

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Old 04-22-2010, 03:12 PM   #2
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By how well they ride and tread to road contact.

My tires say something a lot higher than the 28 lbs I run.
If you run at max pressure, you will wear out the center of the tread.
If you run under inflated, you will wear out the sides of the tread.

If you run too little pressure when you have a heavy load on, it will affect things too.

Jerry Bransford answered this question not oo long ago and gave good suggestions for where to start with different tire sizes.. Sorry, I don't know what the name was, but I'll bet you can find it pretty easily

*edit: found it!
http://www.wranglerforum.com/f5/tire...ion-48817.html

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Old 04-22-2010, 03:17 PM   #3
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I have the same set-up on my unlimited and run 28psi. You can't go by either the door or the tire recommendations when you change your set-up. You can always try the chalk test if you like, but at 28psi, I get a good smooth, quiet ride on pavement and my tire wear is even.
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Old 04-22-2010, 03:30 PM   #4
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What kind of tires are you running, JDsDream - or does it make a difference?

I currently have on Nexen Rodian A/T II tires - came with the Jeep - and will have them probably for another two months before getting new ones.
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Old 04-22-2010, 03:34 PM   #5
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I'm running BFG All terrains I keep them 28-30psi depending on my mood

in the Summer I have a mental block against anything lower than 30psi. But my two cars both require less than this, and I'm getting over it.

and yes the tire model has some effect (sidewall stiffness/load range/etc.)
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Old 04-22-2010, 06:27 PM   #6
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Never go by the tire sidewall that is max pressure. If you don't go too much bigger keep them the same. Jerry answered this on 31's keep it about 30-31psi and if you take it offroad I believe it was 12-18psi. 31 is for regular driving and 33 is when you have you jeep filled and like these guys are saying if you jump up way bigger do the chalk test. The tire itself doesn't make a difference wether its BFG, Goodyear, or whatever it's the size.
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Old 04-22-2010, 06:33 PM   #7
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I ran my 31's at 28 after doing the chalk test... They rode great. Mostly it's just by feel, if it feels stiff, let some air out, if it feels smushy, add some air.
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Old 04-22-2010, 06:48 PM   #8
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Generally speaking, the bigger the tire, the less air pressure it requires to hold up the same vehicle. Going from a 30" to a 31" tire would drop the recommende pressure just a tad from that on your door jamb. I'd probably run them at around 30 psi or perhaps 31 psi if your Jeep is fully loaded. For offroading, you can safely take an All Terrain type tire of that size down to 13 psi on a 15x8 (no wider) wheel, just don't drive faster than around 20-25 mph or on the highway at that pressure.
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Old 04-22-2010, 06:53 PM   #9
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Quote:
Originally Posted by AbbyK9 View Post
What kind of tires are you running, JDsDream - or does it make a difference?

I currently have on Nexen Rodian A/T II tires - came with the Jeep - and will have them probably for another two months before getting new ones.
I run the Goodear Wrangler Duratrac. 31x10.5x15
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Old 04-23-2010, 10:28 AM   #10
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Quote:
Generally speaking, the bigger the tire, the less air pressure it requires to hold up the same vehicle. Going from a 30" to a 31" tire would drop the recommende pressure just a tad from that on your door jamb. I'd probably run them at around 30 psi or perhaps 31 psi if your Jeep is fully loaded. For offroading, you can safely take an All Terrain type tire of that size down to 13 psi on a 15x8 (no wider) wheel, just don't drive faster than around 20-25 mph or on the highway at that pressure.
That was really helpful - thank you! My door jamb actually recommends 29psi for the 30x9.50 tires, so I should be good at 28psi with my 31x10.50s.
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Old 04-23-2010, 11:55 AM   #11
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I have 31x10.50's on 15x8... BFG AT's. I am running 35psi at the moment and it is a little bumpy. I am going to bump mine down to 30 and see where that goes.

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