Jeeping 101: Off-Road Air Pressure

One of the questions I hear most from new Jeepers is “what air pressure should I run?”. And while there is a bit of debate on the exact number, it’s the principle that I would like to focus on today.

From the time we all got our first vehicle, we’ve been trained to “keep the air pressure up”, we see the writing on the tire itself listing the max air pressure and weight, and we hear about how low air pressure can hurt gas mileage. Proper air pressure and safety are synonymous in the minds of most drivers. Sooner or later, however, when a person starts to take their vehicle off-road, they are introduced to the concept of “airing down” – the idea that letting air pressure out of your tires is actually a good thing. This can come as a quite a shock to someone unfamiliar with the concept.

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One time, while our 4X4 club was parked at a trailhead, a first-time wheeler pulled up next to me. I was in the middle of doing my own trail prep (airing down and disconnecting sway bars). I introduced myself and welcomed him. After pleasantries were exchanged, he nervously asked me, “What do I do now?” I quickly replied with a short list of good things to do before getting started. The look on his face was quite puzzled. He sheepishly responded, “You mean we let the air OUT of the tires??”

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Theory

The theory is quite simple: The less air pressure you have in your tires, the more the surface of the tire conforms to the ground, and the larger the contact patch you have. With lower pressure you simply have more of the tire surface grabbing the rock or dirt that you’re trying to climb. This can give you considerably more traction over the exact same setup with a higher pressure.

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There are also more positive side effects of airing down beyond more traction. By making the tire more malleable, the sidewalls will more likely flex around a sharp rock or root instead of being punctured. Another nice side effect of lower pressure is comfort. Having the tires softer allows them to absorb a significant amount of the undulation of the trail, and makes the trail much more enjoyable to drive.

Breaking the Bead

A tire separated from the rim.
A tire separated from the rim.

There are a few concerns with low tire pressure, and while they are all reasonable, they are easy to manage. These include the potential of breaking the seal of the tire and the rim (i.e. breaking the bead), doing internal damage to the tire from running too low, and the problem of airing back up to highway pressure for the drive home. First, I highly recommend purchasing a battery powered compressor. It should be a high-volume compressor, not one of those little ones that plugs into the cigarette lighter socket. These run between $60-$200 depending on volume and quality. I personally have the $60 high volume compressor from Harbor Freight, and while I wish it was a little better, it gets the job done. As far as breaking the bead goes, in the dozens of trail runs I’ve been on, I’ve only seen two broken beads, and they were in extreme situations. They were also no big deal to fix; we simply removed the weight of the vehicle from the tire, and using the previously mentioned $60 compressor, reset the bead. If you don’t have a compressor, remember that it’s heat buildup from under-inflated tires that can cause internal damage, so if you do have to drive to the nearest town to re-inflate, keep your speed to an absolute minimum. I have absolutely putted down a rural highway at 35mph to make it to the nearest gas station 10 miles away.

If you’ve never aired down your tires for going off-road, I encourage you to try it. You will find that it doubles your traction, lowers the chance of tearing a sidewall, gives you a smoother ride, and gives you an overall more enjoyable wheeling experience. And for those who are curious, I prefer to run my tires at 12 psi.

The following video was produced by Tereflex suspensions and has some great info on airing down and as a bonus the end includes a handy tip on dealing with whiny teenagers. 😀

JWK is not affiliated with Harbor Freight Tools or Teraflex! 🙂

7 thoughts on “Jeeping 101: Off-Road Air Pressure

  1. what tire pressure you air down to is more dependent on the actual tire you’re running and what type of wheel is inside it (size, design). Tire like Super Swampers that have very thick and/or stiff sidewalls (some being bias-plies) you’ll want to air to lower pressures than a radial tire, like the ubiquitous BFG/MTs. If you have a slightly narrower wheel (or bead locks!) you can let out more air pressure, as they will keep the bead seated under more sideways pressure than a wider, non-bead-locked wheel. Sometimes terrain can make a difference. A milder trail with fewer large rock obstacles doesn’t need as much airing down.

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