The truth of the matter is...
The truth of the matter is unless your buddy has exactly the same rig as yousame tires, overall weight, etc.you probably should figure out your own air pressure for trail use. Different types of tires flex differently, and different running gear can make a huge difference in the weight of your rig. So you shouldnt just ask the joker camped next to you at the Jamboree what pressure he is running.
Here you can see that the...
Here you can see that the maximum pressure for this tire (50 psi) wont help you much on the trail. Notice that there is almost no flex in the tires sidewall. The tread is holding on to the rock, but only by a square inch or two. This is probably overkill for the road unless you are hauling some serious weight.
Thats what were...
Thats what were talking about: 15 psi is grabbing the rock, and the contact patch is huge compared to high pressure.
Four psi is probably a bit...
Four psi is probably a bit low for these tires. Traction would be great, but dont turn or the bead will pop, plus ground clearance is greatly reduced, and the sidewall is vulnerable.
Just for the heck of it, we...
Just for the heck of it, we took the valve core out of this tire, which means super tractionit also means low clearance because the Jeep would basically be driving on the rim and a few inches of rubber. Note the bead locks, which will hold that flat in place until the rim cuts through the sidewall. Remember that bias-ply tires have very strong sidewalls, and therefore, need less air pressure to conform to the rocks, but they will stand up to lots of abuse.
This may be getting redundant,...
This may be getting redundant, which is to say that we have already pointed it out, but it may be necessary to state again...just kidding. Seriously, bead locks can prevent problems (if not injury or vehicle damage) when aired down. This Jeep was traveling down a steep slope when the bead let go, requiring the Jeep to be winched back onto flat ground so the tire could be reseated.
Heres how airing down...
Heres how airing down can have an effect on ground clearance and still mean the difference between slipping all over the place or gripping the rocks like Spider man covered in chewing gum.
The picture shows tires at...
The picture shows tires at max pressure (30 psi), and trail pressure (4 psi) on the left. The aired-up tires only lifted the differential housing off the rock about 11/2 inches. In some situations a few inches of ground clearance can make a huge difference, while others call for more traction.
Most Jeeps, whether on pavement...
Most Jeeps, whether on pavement or trail, use load-range C tires. This rock flattie uses tires that claim a max-load rating of 2,720 pounds at full (30 psi) inflation. This means the Jeep could be held up by two of these tires at full inflation. Once you add all four fully-inflated tires in to the mix, you have a combined load carrying capacity well over what most Jeeps weigh, so there is little reason to keep all of your tires inflated to full pressure.
Washboards in the sand are...
Washboards in the sand are a good indicator that someone needed to air down more. Note how one set of tracks is wavy while the other set is nice and flat, indicating good air pressurethe jeep is floating on the sand, not digging in.
Experimenting too much is...
Experimenting too much is generally left to either the extremely anal or mad scientists, but playing with your on-road tire pressure can increase tread life and tire performance. The chalk line across the tire helps us establish whether the whole tread of the tire is being used. You can try different air pressures until you find the one thats right for your rig/tire combination.
Make a chalk line all the...
Make a chalk line all the way across the tire, and only drive a few yards. If the chalk line rubs off in the center your pressure is too high (top). If the edges of the chalk line rub off first (bottom), try adding some air. This should extend the life of your tires and keep you from rounding off the edges, or flattening the middle prematurely.
One of the first tricks of the off-road trade has been used for a long time, probably before any one could even engage four-wheel drive because Mr. Fourwheeldrive had not invented it yet. And like many tricks that modern off-roaders use, the first guy who found out that a tire low on air could give you better traction in various types of terrain probably figured this out by mistake. There is a definite advantage to using lower air pressure on both sand and rocks. As for mud, there are two schools of thought that both work depending on the circumstances.
One idea involves tall skinny tires, which grab at the bottom of the mud to keep the Jeep moving (assuming that the mud has a bottom). Airing down will lower the ground clearance and thus defeats the purpose of having those skinnies. So to keep your axles from playing mud anchor, you should keep those narrow tires aired up for maximum clearance. The other method is to run very wide, aired-down tires, which tend to hydroplane across the top of the mud. This method requires a light vehicle with gobs of power to keep those huge mudslingers spinning. And you better be running bead locks or those huge tires could pop right off the rim, and it aint easy or fun to reset a muddy bead on a mud-filled tire. Mud is probably the easiest terrain for popping beads (with sand and rocks trailing a close second and third, respectively), but bead locks are the way to go if you are doing any type of extreme off-roading. They may lighten your wallet, but its worth your sanity and time.
As for airing down, it is at least free, and if you can guess air pressure well and bum some compressor time from one of your pals, then so is airing upthats still no excuse for not having a tire pressure gauge in your toolbox though. If you are spending a lot of time on the trail, you are probably thinking of adding some type of onboard air system. Valve core removers are nice and quick, but you wont be the first or the last to use an environmentally friendly (and free) trailside pebble or back of the valve cap to let some air out when in a pinch.
So you say, What air pressure should I run on my rig? We say that is a loaded question, an intelligent answer that totally depends on the weight of your rig, tire size, and the terrain that you plan on running. Experiment for yourself. Below are some starting points from our experiences to help you get started.