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Airing down discussion


Jerry Bransford

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Some things to keep in mind for airing down. A pressure that you may read works for one tire size won't work for all tires of the same size, and the pressures that work will vary by the tire design and wheel combination too.

The tire's Load Range has the biggest effect. A Load Range E tire is stiffer/stronger than a Load Range D which is stiffer/stronger than Load Range C which is the appropriate Load Range for our Wrangler TJs. The stiffer the tire, the more it needs to be aired down to get the same flexibility and size of footprint. A stiffer stronger tire is simply not as flexible so to get the tire to flex/conform to obstacles a higher Load Range tire has to be aired down further than a lower Load Range tire Plus the design of the tire plus its bead strength will also affect how well or how easily it can stay seated when aired down.

Some say they have aired down to some particular PSI and lost a bead while others have no problems going to an even lower air pressure and never lose a bead. How can that be? That is due to the design of the tire, its stiffness/load rating, and even the wheel's width. A 33x12.50 tire mounted on a 15x8 wheel will be able to stay seated at a lower pressure than the same exact tire can if mounted on a wider 15x10 or 15x12 wheel. The wider the wheel the more air pressure the tire requires to keep its beads seated against the two wheel mounting points that are further apart. So if you're running a 15x10 wheel, a 33x12.50 tire will not be able to be aired down as far as the same tire could be on a 15x8 wheel. And if you were running a narrower 33x10.50 tire it's even more important that you avoid wider wheel widths like 15x10 or (especially) 15x12.

Remember that a tire's advertised width is only its widest width half-way up the sidewall which can be up to several inches wider than its mounting beads. A 33x10.50 tire, for example, will probably have beads that are only 7 or 8" apart which is why you should run a 15x7 or 15x8 wheel for a 10.5" wide tire. Trying to run a 33x10.50 tire on a 15x10 wheel, for example, would result in the tire being forced to position its mounting beads much further apart than they were designed for. So never think that you're supposed to buy wheels the same width as the tire's advertised width. It can work for those seeking that low-rider look for the street but it won't work for the trail as tires that are mounted on wheels that are wider than optimal will cause the tire to unseat very easily.

Just keep in mind that there's no hard-fast rule for what tire pressure is acceptable on any given size tire. It varies, again, by lots of variables so listening to one guy telling you what works for him may or may not work for you.

And keep in mind too that airing down properly can make the difference between a difficult vs. a fun day on the trail. :)
 
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Alex01

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I ran 9 psi in Moab and on the Rubicon trail with 35x12.5x15 MTR /Kevlar on 15x8 wheels. I haven't had an issue yet but others on the last trip popped a bead with slightly higher tire pressure.

Well said Jerry. Each tire/wheel combo is certainly going to be different.
 
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StG58

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So, rumor has it that airing down can actually help an off road tire resist side wall damage. We don't have a lot of rocks here on the wet side, but there's other objects that can cut or puncture a sidewall. What's everyone's thoughts on that?
 

Jerry Bransford

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So, rumor has it that airing down can actually help an off road tire resist side wall damage.
Yes for sure since a softer aired-down tire can conform/flex/bend around the sharp object instead of pushing against it. Like skin softly conforming around a sharp point instead of pushing hard against it and likely being punctured in the process.
 
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StG58

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I haven't noticed any strange tire wear from airing down. But then, I'm aired down, at most, about 25% of the time and going pretty slow most of the time when I am. Bad toe in adjustments are a much bigger culprit. Anyone getting uneven tire wear from airing down?
 

jjvw

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I'm not sure I can point to aired down tires specifically being the cause of odd or uneven the wear while off road. There are things offroad that are less likely to be done without airing down, on the other hand.
 
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StG58

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All of this is what I was hoping for in this thread @jjvw.

Most of the objections I hear to airing down have been addressed here. It's a good thread.

Share some stories where airing down made the difference between making it and not. That's useful.

I know that I now routinely air down and disconnect way more than ever before. The pressures are much lower as well.

Let's hear some stories and examples!
 
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StG58

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Years ago, I recall a discussion about determining the optimal air down pressure. It involved airing down until the center of the tire patch would lift off the ground. That was the point past where the tire contact patch was at it's maximum.

I think this required repeatedly stamping the increasingly aired down tire with a floor jack and cardboard.
So once the tread pattern started to stamp a donut, air up until the donut disappears? Interesting...
 
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Jerry Bransford

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Share some stories where airing down made the difference between making it and not. That's useful.
I was on a moderately difficult rock crawling trail with a couple in a newer Rubicon that was having a lot of trouble keeping up with the group. They had to stop repeatedly and get spotted on relatively easy spots. I noticed their tires were spinning ineffectively where they shouldn't have been. After I finally got the drive to roll his window down (it was hot and he was running his a/c), I asked him what he had aired his down to. He huffily replied "way down" and immediately rolled his window back up. I stopped him again when he was having more trouble and pushed him to get the air pressure he had aired down to. He angrily said "All the way down to 20 psi" and started to roll his window back up when I placed my hand on his window to talk with him. With help from a few buddies, we talked him and his equally angry wife into airing down to 12 psi and they had no more problems. My theory for their anger is they were new to wheeling and didn't know what they were in for when they signed up for the trail we were on. We never saw them again.
 
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jjvw

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A question to those who air down. Who gets asked about your tire pressure?

This happens to me very often as I pass others on the trail. I don't know if this happens to others in our group. Most are visibly surprised when I say 8psi. I don't know what causes them to ask the question.
 

jodomcfrodo

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A question to those who air down. Who gets asked about your tire pressure?

This happens to me very often as I pass others on the trail. I don't know if this happens to others in our group. Most are visibly surprised when I say 8psi. I don't know what causes them to ask the question.
I had a bunch of people on Red Cone ask me that. I was just at 20 since I didn't feel the need to go way down.

But I had to help air down a newer JK (from 38 PSI) and a 98 TJ (from 45 PSI) while up there. The JK guy said he was afraid of driving down the highway at lower PSI. The TJ guy said he had just aired up from 25 to 45 before hitting the trail. I think that was the guy who also offered me a joint for helping him out, so that might explain something...
 
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JMT

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Only thing I can’t remember coming up in the thread is the loss of clearance at the diffs when airing down. IMHO this seems to effect less lifted rigs more than anyone. When we ran on granite we had one guy who didn’t air down because I think he had only 1” lift and 31’s and he was running trails for rigs set up on 3.5-4” and 33’s. He did fine but it was a bouncy ride.
 
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jjvw

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Only thing I can’t remember coming up in the thread is the loss of clearance at the diffs when airing down. IMHO this seems to effect less lifted rigs more than anyone. When we ran on granite we had one guy who didn’t air down because I think he had only 1” lift and 31’s and he was running trails for rigs set up on 3.5-4” and 33’s. He did fine but it was a bouncy ride.
The balancing act between traction and clearance is interesting when it starts to matter. Mine is in a position where it needs the traction of an aired down tire and the added clearance of a larger tire. Particularly where the frame side control arms are concerned.
 
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StG58

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Only thing I can’t remember coming up in the thread is the loss of clearance at the diffs when airing down. IMHO this seems to effect less lifted rigs more than anyone. When we ran on granite we had one guy who didn’t air down because I think he had only 1” lift and 31’s and he was running trails for rigs set up on 3.5-4” and 33’s. He did fine but it was a bouncy ride.
The balancing act between traction and clearance is interesting when it starts to matter. Mine is in a position where it needs the traction of an aired down tire and the added clearance of a larger tire. Particularly where the frame side control arms are concerned.
Well crap (scrambles for tape measure), that explains some things! Assumed some loss of clearance under the pumpkins, but thought it would be trivial, so I never checked. :ROFLMAO:
 

Thunderhead

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I was at 12 psi on my 32’s on the Rubicon before Buck Island. Front left pissed some air on one obstacle and I was down to 10. I went back up to 13-14 on that tire and no more problems. I got it back down to 12 though after Buck Island.
We had 2 others who lost a bead like @Alex01 said
 
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Plumber1

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I must say that I enjoy the ride much much more at 12 PSI than at 28 PSI while off road. Just wondering how much difference it makes between 9 PSI and 12 PSI which is what I usually run at.
 

derekmac

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The change in flex from 5 psi to 8psi is surprising. 8 psi and up hardly wrapped around the extinguisher at all. Excellent visual aid!
I was really surprised myself at the difference. I think I might do this again sometime, but use a bigger rock instead. I think that'll visualize it even better since we might be able to better see the tire wrapping around it.