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Discussion Starter · #1 ·
Ok, newer to the forum and I am trying to get my head wrapped around airing down before going off road. I get it if one is going in sand, but why would you air down for:

1. Mud?
2. Snow?
3. Dirt?
4. Rocks?

I live in Utah and am in the Rocky Mountains all of the time. Lot's of rocks and sometimes very sharp. Would I air down in this scenario? Why? I just want to learn here and this seems like the place to do it. Currently I have a 2003 Jeep Wrangler Rubi with 31 X 10.50 X 15 wheels and tires (BF Goodrich All Terrain TA's) placed on by the PO.

Still not sure if I want to replace them with a more stock configuration or to continue with this. Would love suggestions. Also, my wheel configuration seems to pull the wheel and tire outside of the wheel well even though there is plenty of room. Again is this what I should have? Not sure if I will ever seriously rock climb, however I love to drive in the Rocky Mountains and Utah deserts. Recommendations?
 

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Airing down its a very important even in sharp rocks. The tire deforms and allows to distribute all the weight in a bigger area. Thats the key the only point in airing down.
You will see try to do a slick rock with 30psi without lockers you will spin like crazy 15psi will hug the rock and it wont spin.
Believe me try to do the same thing first with 30 psi and later lower your air to 25-20-17-15 believe its a world of difference.
In all circumstances not only in rocks gravel mud sand snow its the same principle bigger area to distribute the weight.

In my personal opinion i always go to 15 for mud sand rocks and im gonna do only gravel or dirt 20psi.
Btw its also more comfortable since the tires are absorbing the impacts on the rocks not the suspension.
Hope this helps
 

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The usual threshold for being aired down is below 15 psi. Above that & there isn't that much benefit. When I ran smaller stock-size tires on dry rocky desert terrain, I usually ran 11-13 psi.

As said above, airing them down does a lot for you... it increases the amount of rubber on the obstacle for better traction, the tread conforms more easily to the obstacle for better traction, and there is less chance for damage to the tire if it has a little extra give when encountering sharp obstacles that can do things like puncturing a sidewall.

You especially want to air down when you're on deep snow or deep mud, to help your TJ stay on top of the deep snow/mud without digging in.

But for up to just a couple inches of snow or mud over the top of good traction, your tires should be fully aired up to give them as narrow of a profile as possible. That helps them to cut down through a light coating of mud or snow to the better traction below.

I would never offroad in most conditions without airing down, there are just too many benefits you'd miss not to.

One illustration: A new Rubicon owner & his wife were in a group I was on & we were doing some moderately difficult rocky trails. He was fully locked, having lots of trouble, and both he & his wife were pissed at us for leading him on a run that was "way too difficult". Well, it wasn't that difficult of a trail so we verified his lockers were on, they were. Then I asked him if he had aired down & he gave me a pretty testy "plenty" answer but wouldn't say what air pressure he had aired down to.

After lots more trouble on the trail that was delaying everyone, with him & his wife being really pissed/scared, I pushed back on his tire pressure once again since his tires were spinning like crazy & not hooking up on the trail. He gave me a pretty huffy answer of 20 psi. After much back & forth discussion, none of which he was happy with, we insisted he air down to 12 psi which we finally got him to do... no more problems with his Rubicon the rest of the day. :)
 

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Discussion Starter · #4 ·
Thank you both for great information! I will plan on doing so my next trip out. Could one or both of you address my last question regarding my tire and wheel size and the fact that the wheels seem to extend the tire out away from the body instead of more tucked into the wheel well? Is that what I want? Jerry, you have already given me some options on tires, however which tire will hold up aired down to below 20 lbs. I think Jerry, you mentioned you had some Goodyear's kevlar-reinforced MT/R ? How do they wear and are they noisy? (any more than the BF Goodrich's that I have now?
 

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Abe Froman
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From your pictures I am betting you are along the Wasatch front. I would say the Orem area if I can see your pictures correctly. Moab is only about 2.5 hours from Utah county. Go there and try running a trail or an obstacle aired up and then the same one aired down. You will see the difference.

As for your question the rims are offset so they stick the tires outside the flares. That is controlled by the rim offset. Depending where you go to get your state inspection they may fail you as the tires technically need to be under the fender flares. Some shops will not flag this, but some will. Ask around where to take the Jeep or it could be quite expensive to pass state inspection.
 

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If you do plenty of rocks BFG AT is a superb tyre. They are horrid in kud but fantastic in rocks.
 

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Thank you both for great information! I will plan on doing so my next trip out. Could one or both of you address my last question regarding my tire and wheel size and the fact that the wheels seem to extend the tire out away from the body instead of more tucked into the wheel well? Is that what I want? Jerry, you have already given me some options on tires, however which tire will hold up aired down to below 20 lbs. I think Jerry, you mentioned you had some Goodyear's kevlar-reinforced MT/R ? How do they wear and are they noisy? (any more than the BF Goodrich's that I have now?
Goodyear's MT/R tires are not noisy, most consider them to be quieter than average.

The reason your wheels are sticking out as far as they are is because they don't have a lot of backspacing... which is a different measurement than 'offset' is & the two terms are totally different measurements and not interchangeable.

Factory wheels are tucked all they way into the wheel well which means they have a lot of backspacing. Factory wheels have anywhere from 5.25" to 5.5" of backspacing.

Let's compare a wheel with 5.25" of backspacing with an aftermarket wheel with only 3.25" of backspacing. The aftermarket wheel with only 3.25" of backspacing will stick out 2" further out of the wheel well than the wheel with 5.25" of backspacing will. I suspect your wheels probably only have something like 3.25" of backspacing.

The below photo show where the amount of backspacing is measured beween... from the inner-most edge of the wheel closest to the suspension, to the wheel's mounting surface.

What also determines how far a wheel protrudes is its width.

Let's say you have two wheels, one 15x8 and one 15x10. Let's say they both have 5" of backspacing. Since they both have the same 5" backspacing dimension between the edge of the wheel and its mounting surface, that means the outer edge of the 15x10 wheel will stick out 2" further than the 15x8 wheel.

So it's a combination of the wheel's backspace dimension (not Offset which is different) together with its width that determines how far out of the wheelwell a wheel sits.

The second image shows how Offset is measured which is not nearly as useful of a measurement for Jeeps & trucks. Offset is the distance between the centerline of the wheel's tire mounting surface and the wheel's mounting flange.

Hope that helps. :)
 

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Discussion Starter · #8 ·
You are a plethora of Jeep knowledge! So, which is the best configuration for a jeep?
1. Do you want a lot or little backspacing?
2. Do you want or need an "offset"?
3. last but not least do you recommend a "beadlock" wheel for greater security when airing down?
 

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Bead locks won't be required for airing down to 15 or 10 psi. Bead locks allow you to go even lower without losing the bead. For normal trails with a stock or close to stock jeep, I can't see the need for bead locks. I personally ran some trails today first at 30 psi then at 12 and it make a world of a difference in traction and ride quality. Just remember to air back up before hitting the highway.
 

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You are a plethora of Jeep knowledge! So, which is the best configuration for a jeep?
1. Do you want a lot or little backspacing?
2. Do you want or need an "offset"?
3. last but not least do you recommend a "beadlock" wheel for greater security when airing down?
1) The most backspacing possible without causing the wheel or tire to rub on things like the suspension is what you want. The amount of backspacing required is usually most dependent on the tire width. For 31x10.50 tires, you can run as much as 5.25" to 5.5" of backspacing. The less backspacing the wheel has, the more it will stick out unnecessarily. I like to run as much backspacing as possible to keep the Jeep from looking like a skateboard. Also the less backspacing you have, the more tire "scrub" you have which is the tire being swung through an arc when turning the steering wheel left/right instead of the tire pivoting about a point when the steering wheel is turned as it should be.
2) You can forget the term 'Offset' for Jeep wheels, that dimension is more useful for cars & sports cars.
3) Beadlock wheels are not needed or recommended for casual or typical recreational offroaders. Beadlock wheels become needed when you start doing very hardcore difficult trails where ultra-low tire pressures are required.
 

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just be sure you have a quality gauge when airing down. I was up this winter first time with the club I was with we aired down I went to 15 psi, later as it got deeper down again to 12. as I was wheeling my rear tire went off the bead. I came to find out (after ruining that tire) that my gauge was reading 5-6 psi higher than reality. so when it said 12 I was actually around 6 or 7. way too low to run without beadlocks. anyway I ended up getting a new set of 31x10.5s because it was only 100 more than replacing the one 32x11.5. save money buy a quality gauge and deflator. Currie makes a very nice one thats usually around $30. if it saves you just half of one tire it paid for itself.
 

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Discussion Starter · #12 ·
Again, great information from all. To all who responded THANK YOU! There is so much to learn and it is so much easier to ask fellow Jeep enthusiasts who have already paid the price of learning while doing. Last question to Jerry and all; are there companies that you recommend who make a good wheel for jeeps that I ought to be looking at because from this discussion, I want to change wheels along with new tires. By the way, I love my new Rancho 9000XL shocks. Are there any deals out there I ought to know about?
 

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For low pressure accuracy, I use a large round 0-30 psi gauge like the below. Pencil type gauges are the worst for accuracy, & I don't trust digital gauges any more than I trust pencil type gauges either. The 30 psi max indication means it will be more accurate and more easily read at typical low aired-down tire pressures than a 0-60 or -120 psi gauge can be.
 

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Bead locks won't be required for airing down to 15 or 10 psi. Bead locks allow you to go even lower without losing the bead. For normal trails with a stock or close to stock jeep, I can't see the need for bead locks. I personally ran some trails today first at 30 psi then at 12 and it make a world of a difference in traction and ride quality. Just remember to air back up before hitting the highway.

How low PSI can I / should I go to with rockcrawler beadlocks and 35 bfg M/t km2. I will be in the Sand at Pismo Beach. Thank you anybody for your assistance
:popcorn:
 

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Are those rockcrawler beadlock wheels real or simulated beadlocks, and what width are they?
 

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I live in Utah and am in the Rocky Mountains all of the time. Lot's of rocks and sometimes very sharp. Would I air down in this scenario?
In my opinion, that scenario is the best time to air down. There are three main benefits to airing down:

1) better traction
2) decreased chance of tire puncture
3) improved comfort due to smoother ride

In the local rocks and hills, you'll take advantage of all three benefits. That's why I say it is the best time to air down.

Moab is only about 2.5 hours from Utah county. Go there and try running a trail or an obstacle aired up and then the same one aired down. You will see the difference.
You certainly don't have to go that far to see the difference. Even a simple run up AF canyon will be an eye-opener. If you want somebody to go with (because Jeeping rule #1 is Never Go Alone), let us know.
 
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