*REVISED WITH ANSWERS TO COMMON QUESTIONS WE HAVE RECEIVED SINCE THE FIRST RELEASE*
Deflating or “Airing Down” is a mystical and magical secret within the overland / offroad community that can not only increase your traction, but also improve your ride comfort, dampen the effects of rough roads on your suspension components, and protect your rolling stock from puncture against sharp objects.
However, this also has a potential downside as there can be catastrophic consequences if the magic spell is worked incorrectly resulting in a lost bead, or even worse; a blowout. So where is the balance in working with this technique on your own rig?
I had the opportunity to speak with an individual (who shall remain nameless for this article) within a large tire corporation. This particular gentleman was an engineer who helped develop a lot of the tires we run today. He told me (officially) that he can not condone running their (insert brand) tires at a lower PSI than recommended. However, (unofficially) he confirmed that running at a lower PSI under the right circumstances would not degrade the integrity of the tire itself.
That being said; there are several factors to consider when selecting a proper PSI… this was some of his input on the subject:
1) Wheel Size vs. Tire Size
So how much meat (rubber) do you have between the rim and the rock you’re about to hit? If you’re running 15″ wheels with 35 or 37 inch tires you can go down in the 10 PSI range with no issues. If you’re trying to run 18″ wheels then 20 PSI is probably as low as you want to go if there’s a chance you’ll tag a rock. The reason for this is you can actually damage the interior of your tire if you were to pinch the tire between a rock and the rim. This type of damage will go unnoticed until you either remove the tire, or have a blowout…
The rate at which the tire deforms and reforms can have an adverse affect on the sidewall as well. If you’re running 55 MPH down a paved road to a trail head at 18 PSI you’re generating heat in the side wall due to the constant deforming and reforming of the tire footprint. It doesn’t take long to do irreparable damage to a tire under these conditions (which is also hidden to the user). Consider airing up even if it’s just a short run down a hard surface at speed.
This factor goes hand-in-hand with speed. The type of surface you’re running on can make all the difference on PSI selection. For example, if you’re running on sand, the surface itself is helping support the integrity of the tire since it is also deforming to accept the footprint of the tire. You can typically run much lower PSI on sand due to this fact. Rocky trails at slow speeds are also good candidates for lower PSI since you want more deformation to avoid a puncture or cut. Gravel roads would be a bit less forgiving especially if they are hard packed. Consider a medium range PSI.
4) Aggressiveness of Steer
Basically this means; how hard will you been cutting the wheel at speed? You can run 2-5 PSI in sand… in a straight line. If you plan on doing donuts then you’re probably going to blow a bead… and possibly roll your rig if you’re carrying enough speed. Same for rock crawling, if you’re at an extremely low PSI and try to cut hard while in a bind, you’re likely to blow the bead.
Tip: If you do blow a bead… try a heavy duty ratchet strap (kept in the tool kit) for wrapping around the tire while re-seating.
How do you air-down?
We use Staun Tyre Deflators. These can be preset to your optimal tire pressure then screwed on to each tire. They will deflate to your pre-set pressure then stop. You can work on other items while the tires deflate, or even gently drive down the trail until they’re complete.
How do you air-up?
You have many choices of air compressors on the market. An inexpensive unit can be had for under $100 but plan on 45 or so minutes to air-up. If possible make sure you choose a 100% duty rated unit to help speed up the process and reduce the chance of unit failure. If you’re looking for the top-of-the-line, highest quality, run your air-tools on the trail unit, then you’ll want the ARB Dual Air-Compressor here:
How do you confirm pressure?
Here are our typical PSI settings for our 2014 4Runner running BFG KO’s in 275/70R17 Load Range E tires on a 17 inch wheel:
Every day travel: 38-40 PSI front 42 PSI rear. (Yes, it rides a bit rough but fuel milage is best in this range.)
Highway between trails: 30-32 PSI (Used this in Colorado since our route had highways in between trail heads)
Gravel Roads: 20 PSI (24 PSI in rear if loaded)
Rocky Trails: 16 PSI (18 in rear if loaded)
Sand: 10-14 PSI (No sharp turns at speed with this low of PSI)
Mud: 14 PSI
What about the Trailer?
Here are our typical PSI settings for our Turtleback Trailer with 275/70R17 Load Range E tires on a 17 inch wheel:
Highway Travel: 28-32 PSI
Gravel Roads: 22 PSI
Rock, Sand, Mud: 12 PSI
Choose Your Pressure
The final decision on PSI is really up to you. It’s your rig, so experiment with different settings until you find those sweet spots for your unit’s wheels-to-tire size ratio and final weight. We highly recommend investing in some form of quality tire deflators (Please don’t use a key; it takes forever and you’ll damage the valve eventually) and a 100% duty rated air compressor to save a lot of headache and time. Also, get a quality air pressure gauge… that free one from NAPA isn’t going to cut it!
Keep in mind there are a lot of opinions on this subject and you’re sure to hear a lot of conflicting information somewhere along your research. We don’t claim to have it figured out and would love to hear other people’s experience-based opinions on the subject because we are constantly learning and improving.
This article was written to simply to share the methods we have used in our travels, and have found to be most effective with our current rig setup.
If you’ve never done it, we highly recommend you give “airing down” a try on your next trail-worthy adventure and see for yourself what a difference it can make!