235/75 R15 air pressure - JeepForum.com

 
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post #1 of 14 Old 01-30-2015, 07:54 PM Thread Starter
artyup
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235/75 R15 air pressure

What psi on road/off road are Jeeps running with this tire? Looking for the best ride/wear with my LT235/75R15 Big O XTs.

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post #2 of 14 Old 01-30-2015, 07:59 PM
88hatchy
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32?

1997 TJ - Current project: Simple-ish build
1988 Civic Hatch - Runs 12's, gets 30 mpg
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post #3 of 14 Old 01-31-2015, 12:40 AM
TheBoogieman
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30-32 psi.

Quote:
Originally Posted by mrblaine View Post
Springs have one job and one job only and it isn't to affect, determine, or create ride quality.
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post #4 of 14 Old 01-31-2015, 03:07 AM
mesa-jeeper
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I had those size tires on my jeep when I bought it.. I found that 26 psi was the sweet spot for me. Reasonable on and off road performance as well as good wear across the tire surface Soft, but predictable on road. And just enough traction off road that on mild trips, I didn't have to air down to do what I wanted and the ride was still acceptable, meaning I could drive home without airing up, poor airing down. I still have those tires and rims in storage, and put them on for long road trips when I want better mileage vs my 31mtr's that I run currentlywith my horrible 3:07 gears...

I would run 28~30 on road,
15~20 off road...
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post #5 of 14 Old 01-31-2015, 05:30 AM Thread Starter
artyup
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Quote:
Originally Posted by mesa-jeeper View Post
I had those size tires on my jeep when I bought it.. I found that 26 psi was the sweet spot for me. Reasonable on and off road performance as well as good wear across the tire surface Soft, but predictable on road. And just enough traction off road that on mild trips, I didn't have to air down to do what I wanted and the ride was still acceptable, meaning I could drive home without airing up, poor airing down. I still have those tires and rims in storage, and put them on for long road trips when I want better mileage vs my 31mtr's that I run currentlywith my horrible 3:07 gears...

I would run 28~30 on road,
15~20 off road...
15-20 is lower than I thought. Is it hard on the tires to run this low, downside? TP was set at 36 by Big O that seems high to me and I will try 26 to 30 highway and 20 off road. I only had a chance to do a little off road so far but I am very impressed with my little Jeep. Thanks for the input.
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post #6 of 14 Old 01-31-2015, 05:45 AM Thread Starter
artyup
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Trying to understand tire choices I see everyone going to 31'' and bigger tires. What are the advantages/disadvantages to the larger tires? I read its harder on axles and other parts to go big so there must be a positive trade off like floating over sand and higher clearance but what else?
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post #7 of 14 Old 01-31-2015, 05:54 AM
rsurran
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The Assateague National Seashore (MD and VA) posts 20psi as required to go on the beach. My 33's don't seem to have any trouble with that. Truth be known, the beach trail is not very challenging and some guys fudge the required pressure to 25 or so. They also provide an air up station.

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post #8 of 14 Old 01-31-2015, 09:02 AM
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Quote:
Originally Posted by artyup View Post
Trying to understand tire choices I see everyone going to 31'' and bigger tires. What are the advantages/disadvantages to the larger tires? I read its harder on axles and other parts to go big so there must be a positive trade off like floating over sand and higher clearance but what else?
Bigger tires roll over bigger obstacles easier.
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post #9 of 14 Old 01-31-2015, 03:02 PM
Jerry Bransford
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Quote:
Originally Posted by artyup View Post
15-20 is lower than I thought. Is it hard on the tires to run this low, downside? TP was set at 36 by Big O that seems high to me and I will try 26 to 30 highway and 20 off road. I only had a chance to do a little off road so far but I am very impressed with my little Jeep. Thanks for the input.
You're not airing your tires down for offroad use until they're significantly under 15 psi. Yes, really. 20 psi won't help at all offroad and will just make it more likely you'll be spinning tires or damaging them.

When I was still running the factory size tires, I consistently aired down to between 11 and 13 psi. Never lost a bead, never any tire damage, minimal tire spin. Airing down enough allows the tire to better conform to the terrain for better traction, and it also makes it less likely to be punctured by something sharp like a stick or rock.

Quick story... I was on a moderately difficult trail with a large group and a new Rubicon owner was having a LOT of trouble on the trail, more than he should have with a Rubicon. He was slowing the group down and we are all frustrated with his problems getting up & over even easy obstacles. We made sure he was engaging his lockers and when asked what air pressure he had aired down to, he very huffily answered "way down" and rolled his window back up for the a/c because it was too hot outside for him and his wife. They were pissed off early-on thinking they had gotten in over their head on a trail that wasn't all that difficult but it was really just because they hadn't aired down enough.

About the third time I walked up to his window to ask what his air pressure was after determining it was simply too high for the trail, I pushed him enough to where he finally heatedly answered 20 psi. After much pushing and insistence, we finally got his factory size Rubicon tires aired down to 12 psi. He had no more problems the rest of the day and we were all much happier.

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post #10 of 14 Old 01-31-2015, 04:12 PM Thread Starter
artyup
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Good info Jerry, thank you and thanks for all the info Jeep Forum, I'm learning a lot.
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post #11 of 14 Old 01-31-2015, 04:32 PM
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11-13psi regardless of tire?
I believe my 33" DynaPro ATM are 10 ply. No issues with the bead, even with the stiffness of a 10 ply?

I have been doing fairly light wheeling (due to having small kids in back), with some steep climbs with rocks about twice the size of basketballs. Not huge, but big enough. I've aired down to roughly 20-22psi.
So clearly, that isn't low enough to make an appreciable change in tires function?
Thanks in advance,

~Chris
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post #12 of 14 Old 01-31-2015, 04:48 PM
Jerry Bransford
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You typically need to go to even lower pressures for tires with extra plies. The stiffer the tire, the lower the pressure needs to be so the tire can conform to trail obstacles for best traction. Airing down to only 20-22 psi isn't airing down enough to help.

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post #13 of 14 Old 01-31-2015, 05:17 PM
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Thanks for the info.
Much appreciated.
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post #14 of 14 Old 01-31-2015, 06:54 PM
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Quote:
Originally Posted by Jerry Bransford View Post
About the third time I walked up to his window to ask what his air pressure was after determining it was simply too high for the trail, I pushed him enough to where he finally heatedly answered 20 psi. After much pushing and insistence, we finally got his factory size Rubicon tires aired down to 12 psi. He had no more problems the rest of the day and we were all much happier.
I ran into a similar situation with a guy who had a stock Rubicon. I asked him what he was running for tire pressure on the trail, his response was 35 psi. Then I asked him what pressure he was running on the road, he responded "50 psi".

After trying to explain to him about tire pressure, I gave up. He knew everything, all you had to do is ask him.

I told him "have a nice day" and went on my way.

I run 10.5 psi on the trail (it does burp sometimes in the rocks) with 35x12.5 tires and 28 psi on the road, my Jeep weighs 5000 lbs...
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