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Old 08-09-2011, 03:33 PM   #1
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Quick Tire Pressure Question

Just wanted to know what is a good starting point for TP in 33x12.5x15 rocky mountains? What do you all run on the street and then what do you air down to for off road? I don't have any extra bumpers or anything right now. It's just a normal TJ that is lifted 3" with bigger tires. Thanks!

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Old 08-09-2011, 03:37 PM   #2
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I don't know anything about those tires. But i'd say a good starting point for a C load range 33x1250 is between 20 and 25 psi. I have been running 24 lbs in mine and they have been wearing great.

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Old 08-09-2011, 07:14 PM   #3
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For a 33x12.50x15 supporting a Wrangler, 26-28 psi is appropriate. 26 around town with just 1-2 people, 28 when fully loaded.
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Old 08-12-2011, 02:23 PM   #4
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How about a 33x10.50-15? I have 28 psi and the sidewalls are very flexible.
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Old 08-12-2011, 02:28 PM   #5
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How about a 33x10.50-15? I have 28 psi and the sidewalls are very flexible.
I normally run 28psi in my 33x10.5 KM1s and it seems to work well .
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Old 08-12-2011, 03:10 PM   #6
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What about 31X10.50 28 psi the same?
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Old 08-13-2011, 03:06 AM   #7
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When I bought my TJ it already had the 33x12.50 Toyos on 18" rims. The PO said that the shop recommended to him that he run them at 50 psi. Does that sound right, or should I let some air out?
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Old 08-13-2011, 03:32 AM   #8
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Hell yes, let some air out! 50 psi is not just going to ruin the center tread of your tires, it's going to ride like hell and probably dangerous.
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Old 08-13-2011, 03:43 AM   #9
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I'm a fan of the chalk test. Go to a level parking lot or quiet street. Draw a inch thick line with chalk across all 4 tires. Drive slowly without turning as much as possible. If the line wears on the inside first, you're over inflated. If it wears on the outside, your under inflated. I usually take air with me, but I bet just a tire gauge is necessary, you won't believe how low you'll end up- especially if your running 50 lbs.
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Old 08-13-2011, 09:11 AM   #10
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So I lowered mine down to about 26 and it definitely rides better but now with the extra bulge I rub on some part of my steering components at a full turn. I never noticed it before when it was higher. I'm not sure what I can do besides new wheels or spacers. These wheels have 4" of backspacing and I was assured by the shop here that I would not rub at all. I guess I could fight them on that and maybe get my money back or something since they guaranteed something that was not true. Any suggestions?
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Old 08-13-2011, 10:17 AM   #11
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So I lowered mine down to about 26 and it definitely rides better but now with the extra bulge I rub on some part of my steering components at a full turn. I never noticed it before when it was higher. I'm not sure what I can do besides new wheels or spacers. These wheels have 4" of backspacing and I was assured by the shop here that I would not rub at all. I guess I could fight them on that and maybe get my money back or something since they guaranteed something that was not true. Any suggestions?
Put a washer or two on the steering stops. That will prevent rubbing at full lock. Airing up a pound or three will help too probably.
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Old 08-13-2011, 12:42 PM   #12
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Quote:
Originally Posted by Powertrip View Post
When I bought my TJ it already had the 33x12.50 Toyos on 18" rims. The PO said that the shop recommended to him that he run them at 50 psi. Does that sound right, or should I let some air out?
Whoever recommended 50 psi needs to be either educated or if he's obstinate, forever banned from the automotive industry. He probably said 50 psi because he may have seen 50 psi on the tire's sidewall which is NEVER the correct air pressure to use. The sidewall's air pressure is only its maximum safe pressure which would only be correct if the tire was forced to carry its absolute maximum safe load which should never be done. Our tires normally only carry perhaps 50% of their max safe pressure which is for safety reasons. For that reason, our tire air pressures should never be set to what is on the sidewall.

26-28 is a good air pressure range for a 33x12.50 tire carrying a vehicle with the weight of a Wrangler... 26 when the Jeep is unloaded, 28 psi if it's fully loaded. The correct air pressure is totally dependent on the vehicle's weight so the same tire will have different "correct" air pressures for different vehicles with different weights.

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Originally Posted by HarryJeepGuy View Post
I'm a fan of the chalk test. Go to a level parking lot or quiet street. Draw a inch thick line with chalk across all 4 tires. Drive slowly without turning as much as possible. If the line wears on the inside first, you're over inflated. If it wears on the outside, your under inflated.
Be wary though as using the chalk test as the sole indicator is a very common cause of under-inflated tires. A heavy-dose of experience and common sense needs to be part of the chalk test where determining the proper air pressure goes. Underinflation can often be a bigger problem than overinflation.

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Put a washer or two on the steering stops. That will prevent rubbing at full lock.
X2 and here's how to do that... Jeep Steering Stop Adjustment
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Old 08-13-2011, 03:06 PM   #13
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Awesome, thanks so much! That's an easy fix for sure!
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Old 08-13-2011, 10:21 PM   #14
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Thanks guys, I'm looking forward to a much softer ride!!
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Old 08-13-2011, 10:47 PM   #15
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I get a nice wear pattern with 29psi up front and 28psi in the rear.
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Old 08-13-2011, 10:53 PM   #16
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Great info, I get a small amount of rub at FULL turn as well. Glad its THAT easy to fix. One question though, will this limit the turn radius? (I know not much at all, but am I correct in assuming that by adding the washers you are limiting how far the wheels will turn?)
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Old 08-13-2011, 11:08 PM   #17
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Yes it does reduce your turn radius.
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Old 08-13-2011, 11:34 PM   #18
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I have bfg km2's 235/85-16 (32") load e. They say 80psi. I've always kept them around 60-65psi. Opinions?
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Old 08-14-2011, 03:26 AM   #19
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Mike, haven't you noticed your tread wearing out in the middle of the tire only? That has to ride like hell. Off hand, and I've never run 32's, I'd say that 32 front, 30 rear is closer to where you should be. A few lbs in either direction depending on how your set up, but you're way over.
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Old 08-14-2011, 08:16 AM   #20
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Here's a quick and easy way I learned for figuring out the best tire pressure. I learned this from drag racing. It might not apply to Jeeps, but I don't see why it wouldn't.

1. take a spray bottle filled with water and spray a section of your tire tread with the water.

2. roll your vehicle forward on a clean dry surface so the sprayed section of tire leaves a water mark on the pavement.

3. if the mark is darker in the center, and faded on the edges, your pressure is to high, if the mark is dark on the edges and the center is faded looking, your pressure is to low, if the mark is nice and dark and well defined all the way across, then you're right where you need to be.

Everyones rig is different, so tire pressure is best adjusted to your rig, not what someone else is using.
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Old 08-14-2011, 08:41 AM   #21
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Sounds like an easier version of the " chalk test", which I guess isn't a great idea... I don't see why it wouldn't be a good starting point, instead of wearing the middle of your tread to figure it out. I wouldn't go below 20 or above 30 for on road driving. Rest depends on your setup. Just my opinion.
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Old 08-14-2011, 08:54 AM   #22
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Quote:
Originally Posted by Mikekaz1
I have bfg km2's 235/85-16 (32") load e. They say 80psi. I've always kept them around 60-65psi. Opinions?
That is the pressure I would run if those tires were mounted on a heavy truck or something. Your Jeep is super light for those tires so you need less psi.
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Old 08-14-2011, 09:47 AM   #23
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That is the pressure I would run if those tires were mounted on a heavy truck or something. Your Jeep is super light for those tires so you need less psi.
Hmmm ok then. Thanks everyone
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Old 08-14-2011, 11:09 AM   #24
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I have bfg km2's 235/85-16 (32") load e. They say 80psi. I've always kept them around 60-65psi. Opinions?
That's crazy-high for 32" tires supporting a vehicle the weight of a Wrangler, 32" tires should be no higher than 29-30 psi.
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Old 08-14-2011, 03:02 PM   #25
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That's crazy-high for 32" tires supporting a vehicle the weight of a Wrangler, 32" tires should be no higher than 29-30 psi.
I'll be changing soon then!
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Old 08-29-2011, 11:12 AM   #26
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What about 31x10.5?
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Old 08-29-2011, 12:55 PM   #27
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I am running my 31x10.50x15 Trail diggers at 23 lbs all the way around and it looks like they are wearing evenly. Ride is nice as well.
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Old 08-29-2011, 01:15 PM   #28
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I am running my 31x10.50x15 Trail diggers at 23 lbs all the way around and it looks like they are wearing evenly. Ride is nice as well.
Mine had Mastercraft Courser AT2s on it when I bought it all of about 2 weeks ago. Sticker on the door jamb says 29 psi for the OE 29s so I wanted to double check.
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Old 08-29-2011, 01:18 PM   #29
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I am running my 31x10.50x15 Trail diggers at 23 lbs all the way around and it looks like they are wearing evenly. Ride is nice as well.
That's too low for a 31" tire. 29-30 psi is correct for that size tire supporting a vehicle with the weight of a Wrangler.
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Old 08-29-2011, 01:30 PM   #30
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I have bfg km2's 235/85-16 (32") load e. They say 80psi. I've always kept them around 60-65psi. Opinions?
I run 245/75R16 on a 2500 extended cab long bed truck. I run them at 55 psi unless I'm towing or throwing a ton of crap in the bed... That is way to high for a jeep

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