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Guest Message by DevFuse

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Why air down your tires? and how Low? small article i found for all you 4wheelers

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15 replies to this topic

#1 Rooinater


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Posted 06 September 2003 - 11:15 AM

"Why air down?

Airing down does two basic things to help us maintain traction. First, it allows for a longer and wider footprint. This is important because the more rubber you keep in contact with the terrain, the more traction you will have. In many cases, you can increase your contact with the ground over 200% by airing down. This will increase your overall traction as much 800% assuming you have 4 tires on the ground.
The second thing airing down does for us is that it allows the tire to conform to uneven surfaces. If you imagine your foot for a moment in heavy boots standing on a log, you can see that only a very small portion of your foot is actually in contact with the log at any time. Remove the boot and stand on the log with your bare foot, and your foot can bend and conform to the log giving you a much more firm grip. Tires need to do this when trying to get grip over rocks, gravel, sticks, etc. The difference is truly amazing. An added side benefit is that reducing the pressure in your tires softens the ride tremendously while off-road.

How much air should I use?
This is an issue of MUCH debate. Land Rover recommends that the stock tires should not be aired down below 16 psi in the front and 25 psi in the rear. In truth, with a standard load in the rear, this is probably good advice. If you take out too much air, you run the risk of rolling the tire right off the bead. This is very likely with the stock tires since they really don't grip the rim all that well to begin with. With off-road tires in the larger sizes, you can go lower. I have had my 215/85r16 tires at 12 psi without trouble but I don't recommend going that low. I will defer to a chart provided by Oasis-Offroad. They have taken the time to determine optimum tire pressures for off-roading for a range of different sized tires on vehicles of different weight. While the chart is by no means comprehensive, it does offer good insight into what you should be looking at. Please note that Oasis maintains no responsibilty for the accuracy of this chart and bears no responsibility if you have a loss.

Posted Image

So you can see that this is really not a complicated affair, but one that every off-roader should pursue if you want maximum traction off the road. One thing of note. If you plan on airing down off the road, be SURE you have a way to get air back into your tires when you are done."

article by j of Arizona Backcountry

Thought this would be some interesting info for all you four wheelers out there without having to join this club.

#2 ezapar



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Posted 06 September 2003 - 12:06 PM

Ken aired his swampers all the way down to 40 lbs for the Rubicon. :burnout:

#3 Qman


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Posted 06 September 2003 - 12:08 PM

I hate to let the "air" out of this theory but...

When we got to the Rubicon I started to air down for that exact reason but it was suggested(by my co-pilot) that I wait until I absolutely needed the extra traction. Well, long story short, I ran the trail at street pressure and maintained my overall clearance and had no traction issues. The only time I have had problems with my tires in the past is when I aired down.

I should add that most of the people who air down have much larger and stronger engines then our Subes have. They air down to help eliminate tire spin as much as traction.

#4 TheSubaruJunkie



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Posted 06 September 2003 - 12:14 PM

Yeah. The jeepin buddies of mine that I go out with air down no matter where they are going. I've only had to air down once and that was for snow. We call it Sierra Cement. I had my subie down to 12psi at each tire. Any lower and i was affraid I was going to pop a bead. I noticed with the tires aired down, my engine was almost gutless. But with the snow, you just need to maintain a steady speed and make sure you have no wheelspin.

One of my jeepin buddies has beedlocks, and he can air down to 8psi easily. That with all his crawling gadgetry... he can go almost anywhere.


#5 Adam N.D.J.

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Posted 06 September 2003 - 04:53 PM

When ever I go out to the dunes, I usually air down my tires to 20-25psi in the rear, and about 15-20 in the front. (depending on load). But sand is a whole other bag than mud or rocks. Street pressure for my tires is 55 psi, so thats down quite a bit.
Subaru's really shouldn't air down for rocks and whot not, cause too much traction can cause you to destroy axles, (or stubs in the diff's) Some slip is better on the drivetrain. I've learned that one the hard way.

#6 archemitis


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Posted 06 September 2003 - 05:20 PM

and airing down is only good when you have like 26inch tires or bigger. if you aired down some 13 inch 185/80s you would just loose too much ground clearance, and chance hurting a wheel. but on my 4runner with 31s its awesome to run 15lbs! makes all the difference some times. and the bfgs and lots of off road tires have side treadsl, so they turn into ground treads. some offroad articles i have read say if you have never broken a bead, you run too much pressure. dont know about that though

#7 TheSubaruJunkie



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Posted 06 September 2003 - 05:27 PM

Yeah, funny story regarding 13" street tires and airing down.
My father's answer to everything off-road related is airing down your tires. everytime I explain a story about me and off-road, he always asks "did you air down your tires?"

One time I was off-road with my Wagon, before the lift, before the tires. I was running 175/70R13's, bald street tires and i was stuck in the mud. Picture:
Posted Image

Anyhow. when my father came to pull me out, the 1st thing he asked was "did you air down your tires?" After I said no, i explained why.
So, he came with his '94 Jeep Cherokee, with a 4" lift and some larger tires with mud tread. came to the hole, aired down his tires. After he got stuck in the mud, with the aired down tires and all... he started to rock the jeep back and forth. Until the front axle snapped.
Posted Image


#8 soobme


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Posted 06 September 2003 - 06:30 PM

After wheeling for 14 years, in every thing from Baja bugs to a Jeep wagoneer, and being on each side of the fence on this one. I think it all depends on the driver, the rig , and the specific terain. There are times to run street presure, and times that it will get U stuck, or worse yet, a flat tire. Airing down will help with traction, floatation, and punture resistance. But some times one, or all three of those are not a concern, or they are in the other direction( U want less of them). And some drivers have no idea how to take advantage of lower presure in there driving style, so it would be pointless. I do, and more often then not, I air down. That's NOT to say that every one needs to, but it works for me and it has worked for others. To those who do not, life has GOT to be eazyer;)

#9 MilesFox


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Posted 07 September 2003 - 03:56 AM

its like these highschool kids see me powerslide into mac d's parking lot, and they are like cool.
and i am like get a subaru, they are pimp. and they are like,wei like 2wd. i'll stichk to my crapalier.
and i am like what about the baja'n
and they are like i'll get a jep
and iam lilke, but jeep didnt make a turbo!

and then i get fired for putting stickers on the drive thru

#10 Rooinater


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Posted 07 September 2003 - 03:55 PM

depending what terrain i'm running is to how much i air down. like when I went up lake isabele trail. it was being a pain to get traction, my car was hopping and that's what killed my axle.. so i aired down and gee i had tracition and got right up the rocks. i was running like 8 to 9psi( only because the tires cooled down when we had snow starting to fall.) If i'm just driving some where to play on some small stuff, or a quick trip, then i keep highway pressure, which isn't more than 25 psi with the bias ply tires i had.

i usually run around 12 psi cold with my old tires, now i need to find a happy medium for my new tires. if i don't air down it's a lot bumpier and more impact when a tire comes back down, along with i do notice the traction difference.

not airing down makes my car bounce all over, and i break more stuff, so there's no way are you talking me out of it. i see too many benifits, and to little draw backs not to.
1. less bumpy
2. less impact on parts when tires comes down
3. better traction

1. largest drawback you might lose a bead (been there done that)
2. lose a small piece of diff clearance, (not enough to worry about, 8psi up isabele lake tr.)

i've been 4x4ing since i was 11 and i've seen situations that go both way's for airing down. but i've seen a lot more benifits come from airing down. judge your terrain and what your comfortable with. just trying to give you guys an article for those who air down to take estimates to find there happy medium for airing down.

#11 beauregaardhooligan


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Posted 07 September 2003 - 05:07 PM

I aired FERTHER's 185/80-13s down to 20lbs. to run on the Outer Banks. Went right thru it. Clearance loss, maybe 1/2", wasn't as much of an issue in sand.
Works well in mud and snow also.
If you air down too far, under 10lbs, the contact patch can bow up in the middle and lose contact.
Good advice about not airing down till you need to.

#12 soobme


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Posted 07 September 2003 - 05:24 PM

Yes, it's nice to have a trick up your sleeve when U don't know the trail. But if U know what U are geting into before hand U know what presure U sould be using.

#13 Rooinater


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Posted 07 September 2003 - 06:12 PM

wether you have a bow or not at that low of a speed is not the issue. because your tire will conform to whatever rock or root is in your way. and when each tire holds 2855lbs a tire at 10psi ain't nothing, there is no bow let alone a lot of tire squat. you need to know your tires and i know mine, and what they can be at. my tires were thick 6 ply bias ply's. the weight of my vehicle couldn't hardly get them to began squating till i get to 14psi. and over 25psi they hardly touch the ground but a strip down the center.

#14 sandhappy


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Posted 07 September 2003 - 11:20 PM

The very first time I took my Sube to the dunes I tried to not air down at all and see how far I could go. My car was really straining to get around and it was totally gutless. I then aired my tires down to 15lbs, and it helped out BIG TIME because the car just floated on top and never spun a tire. On my last trip to the dunes I got this thing totally stuck, and there was no one for miles to help. As a last ditch effort I aired all the way down to 9lbs. My car came right out of the hole it was in, and went EVERYWHERE the rest of the weekend. Keep in mind that these tires are 31x10.50x15's, but I am going to use it at that pressure from now on!!

#15 baccaruda



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Posted 08 September 2003 - 12:35 AM

would the lesser weight of our subarus matter, vs a V8 vehicle's weight?

#16 Rooinater


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Posted 08 September 2003 - 08:30 AM

just means you;ll be less likely to lose a bead. they have more weight tearing at the bead at a lower pressure.

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