Air down or not?

My most rugged off roading is done in an area of granite lava flows. This makes for a lot of slick rock, large rocks, ledges, and "potholes" in solid granite. Most if not all of these obstacles are height driven, so the more clearance, the better.

My original 4X4 was a Chevy S-10. The only lift I had on it was larger tires. My uneducated logic was, why would I air down? Airing down could make me lose a small amount of height, plus make me sink even more coming off an obstacle as the tire compressed. Now that I have my Commander, I am surrounded by those who air down for 4 wheeling.

So my questions to the forum are: Do you air down, if so how much, and what (besides ride comfort) are the ups and downs?

I air down on most trails/roads that are not smooth, my purpose is to make the ride a smooth as possible. I do not drive in sand or mud (there is none near where I live) so that is not a concern and I feel my current tires and the power of the Hemi will move me through or over almost anything. But on the longer rides it is nice to have a smooth ride and reduce the jaring as much as possible and for that reason I will air down to about 25Lbs of presure.

Another reason for airing down is that your tires will deform and get better traction on large rocks and especially on granite slick rock out west if they have lower air pressure. I have seen some actually wrap themselves around the curve of a rock. Too low of air pressure can however cause them to come off the wheel rim. I have gone down to as low as 15 psi when I used to do more hardcore rock crawling with my last TJ on trails like the Rubicon, Dusey Ershem, or Kaiser pass in California. As Jon mentioned the best ride comes from lower air pressure where the tire is not rebounding from the rocks or trail.
Many of us carry air compressors mostly for airing up. We actually had a give away of free air compressors on the first Sedona Trail run.

Well I have been rock crawling both ways. Not airing down is diffidently a bouncy ride. It also makes obstacles harder to get over approaching a rock fully inflated your tires first action is to bounce off the rock. The same rock aired down like Huey said the tire will actually conform to the rock and you just crawl right over. I to was concerned about ground clearance and was the reason why I did not want to air down but really how much can we be loosing. All the guys I went with aired down to 16PSI and they had no issues. I have never had to air down at the beach yet even though I see people stuck all the time including my bro's wrangler following me but If I ever do get stuck on the sand I would air down 20PSI and drive away. So for sand mud feel it out I guess but rocks and stuff I would air down.

I confess that I personally don't air down as far or as often with my XK as I did with my old LJ.

In the majority of Jeeping conditions the air-down advantage is predominantly about ride (like the above posters noted). My ride is already so much more cushy in the Commander that not airing down results in the same bouncing I got after lowering the LJ. So a lot of times I just don't bother, even though I carry a portable compressor in the rig for quick airing up.

On the other hand, there are Jeeping conditions that simply demand air-down. The clearance loss is minimal, and you get much better traction over rocks as the tire flattens out (and you lose the "bounce-off" and such, too). In those cases, I go down to 20 or so with my 285s. Nicely squishy with little chance of popping the rim.

I aired down on the beach to 25 lbs. I didnt try it without airing down and I did see a bunch of people stuck. i had no problems at all.

Has anyone noticed a difference in tire wear? How about the chances of getting chunks taken out by a sharp spot? Logic seems to tell me that a squishy tire's tread would be less likely to be rigidly pushed into a sharp spot, but more likely to try to "hold" onto a sharp edge of a ledge instead of cleanly rolling off.

Airing down seems like it would make for more exposure to the sidewalls by rolling them outward and closer to the ground?

Airing down for Black Bear Pass in Colorado I ended up with a few chunks missing from my tread. The Chute area was similar to what I do here in CA, and I normally do not lose chunks from my tire treads. These are new tires though, so I don't know if it is the tires or the airing down that is more at fault.

I air down everytime I go off roading. Usually I air down to about 16-18 psi.

well if you have Mt's or AT's something other then street tires they are actually made to be aired down. Thats were the importance of how many ply's your tire's have and such. Maybe discount tires can chime in on the subject.

terrain, tire and rim selection will dictate the tire pressure you will run.

i am a rock crawler & i run 35 / 12.50 / 15's on a rim that is 8" wide. i typically air down to about 9psi. my buddy that runs bead lock keeps his about 3-5psi. when i had rims that were 10" wide i was having problems with "burping" air from the bead at 12 psi. IMHO a fully inflated tire is more prone to being punctured as it is not going to flex. thing of a fully inflated balloon and how easily they pop, but with it half inflated it is more yielding. for research purposes, go out to your jeep and measure the bumper height front and rear. air it down and measure again. it will be a nominal difference. a tall sidewall like i have (10") will have more flex and will have a larger difference from fully inflated to aired down. but with a larger rim size like 17" and a 32" tire (about 7") will have much less difference.

Quote:

---

Originally Posted by Doc in AZ

IMHO a fully inflated tire is more prone to being punctured as it is not going to flex.

---

I fully agree on Doc's statement. I have experienced that myself a couple of years ago. We were riding a trail in Big Bend National Park (TX) which was covered with little very sharp rocks. Since I didn't air down I punctured two tires. I ended up plugging the tire with the smallest puncture with the biggest screw I could get off my Grand Cherokee (one in the rear hatch). It worked and got us of the trail to the repair shop within the park. I have to say, it was good learning experience for me. I was just starting offroading and ofcourse had no repair plugs with me and not much experience airing down tires.

For me airing down is essential for traction and preventing puncturing the tires.

I air down to about 25, lower if it's really muddy. My duratracs are load rated E and have very stiff sidewalls. I barely see a difference in the sidewall height taking out 20 PSI (I run on the streets at about 45psi), but the traction and ride off-road are considerably better. I too lost some chunks on Black Bear, but there were no punctures!

Quote:

---

Originally Posted by brendon

I air down to about 25, lower if it's really muddy. My duratracs are load rated E and have very stiff sidewalls. I barely see a difference in the sidewall height taking out 20 PSI (I run on the streets at about 45psi), but the traction and ride off-road are considerably better. I too lost some chunks on Black Bear, but there were no punctures!

---

25 psi is what i run on the street... why would you be running 45 psi on the street? just because there is a max pressure on the sidewall doesn't mean that's the recommended pressure for all vehicles. that max pressure rating is for max load capacity. i'll bet you dollars to donuts that if you run your rig across teh scale it's only about half what the max tire rating is.

on my old work truck the tires were rated at 75 psi. when i was empty i ran about 40-45 in the rear duals and about 55 up front. fully loaded GVW 14.5K lbs, i had the front at 65 and the rears at 75.

The max rating on my tires is 75, so even at 45 I am no where near the max. The stock recommended pressure for the Commander is 36 on the stock tires. These tires (Duratrac) recommend a normal pressure of 40 for the Commander. On the street, I run all my tires a little over the recommended pressures as my personal preference for driveability, and because I often do have a full load in the vehicle.

i would keep an eye on the tread wear as a good indication of proper tire inflating. an over inflated tire will wear more quickly in the center, under inflated will wear more at the edges. you can always do the chalk test to insure you are getting a good contact pattern.

The reasson to air down your tyres is not just for grip. If the tyres are at normal pressure and you hit a small sharp stone at speed, it will ripp the inside of the ply on the inside of the tyre and over time will cause the tyre to blow out when you drive at speed on the free way. Any time you get on a dirt road I would say deflate to 1.5 bar, eaven if you have road tyres on the Jeep. As sson as I get on a dirt road I deflate to 1 bar, but I have 33" BF A/T tyres on my Commander.

And the measurement device for finding the "bar" on your "tyre" ... do you keep it in the boot? :)

Well, after spotting a couple of XK's over obstacles one guy had a bunch of trouble making it and I was confused at to what the problem was. Then it hit me he said earlier he didn't air down what a difference it makes uh. During the first day we headed down some long rocky service roads. About an hour into it I got fed up and air downed to 25PSI and instantly my ride smoothed right out and the family was happy again and the wife just wanted to know why I didn't do it an hour ago.

1.5 barrs = 21.7 lbs/in^2
1 barr = 14.5 lbs/in^2

Arrie is our friend in South Africa, so I guess they use barr as their unit of pressure over there. Actually, I wonder why they don't use kilopascals, but it's just a factor of 10.

:cool:

I air down to lower than 15 psi when driving on soft dry sand ,, I also put it on around 10 psi when going to extreme soft sand and tough areas, and even with such pressure we sometimes get stuck

Don't you risk breaking the bead at such low pressures...?

Quote:

---

Originally Posted by lekmedm

Don't you risk breaking the bead at such low pressures...?

---

no your still good down to 15PSI but I wouldn't go much lower then that with out bead locks IMO

I have never popped a bead and I always air down that low.

In Western Australia you do a lot of beach work and also sharp, rocky terrain in the north. We air down for both, rocks approx 25psi. With sand it is a bit dependent on the make and style of tyre you are running, they have different deflation characteristics.
With sand you are trying to lenghen the tread footprint, with one of your tyres at normal pressure slide a ruler under the front and rear at a right angles then mark on the pavement the contact lengh. Now reduce the pressure and do the same again, you will soon see once you get under 18psi you get huge improvement in footprint. We normally drop to 20psi then if you get in trouble you can still drop further to get out. 12psi is the lowest I would go to without beadlocks and you would pump up as soon as you hit firm ground because a lot of sidewall is on the ground.

http://www.youtube.com/watch?v=CKK8DGhTP78

Great video SAL. The tire's integrity is something alot of us forget about. Airing down sure helps to keep your kids from becoming scrambled eggs in the back seat as well.

If you go to there youtube page the have a series of videos that include how to pick a compressor for your needs. And check out there project trucks it pretty bad ass

Quote:

---

Originally Posted by 07JeepXK

I have never popped a bead and I always air down that low.

---

So what do you air down to? 15? or lower? Sal's post suggested not going below 15. I have run on flat tires without
popping a bead but it shouldnt be done....

Quote:

---

Originally Posted by Sal-XK

If you go to there youtube page the have a series of videos that include how to pick a compressor for your needs. And check out there project trucks it pretty bad ass

---

I got the one from Harbor Freight, it's nice but runs hot. Have to let it cool about 30 minutes before putting it away.
superacerc: like your comment. maybe that's what happend to us all. Too many years of bouncing around