Overland Traveling Magic
Deflating or "Airing Down" is a mystical and magical secret within the overland / off-road 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.
What PSI does Lifestyle Overland Use?
Here are our typical PSI settings for our 2014 4Runner running BFG KO2's in 285/70R17 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 mileage is best in this range.)
Highway between trails: 30-32 PSI (Highways in between trail heads.)
Gravel Roads: 20 PSI (24 PSI in rear if loaded)
Medium Rocky Trails: 16 PSI (18 in rear if loaded)
Heavy Rocky Trails and 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 285/70R17 Load Range C tires on a 17 inch wheel:
NOTE: THIS IS WITH THE NEW ICON COIL-SPRING SUSPENSION
Highway Travel: 32-34 PSI
Gravel Roads: 25 PSI
Rock, Sand, Mud: 20 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!
THE PRODUCTS WE USE
Automatic Tire Deflators
Model: 6-30 PSI
These are some of the first items we ever put into our kit and they have been rock-solid ever since. There are many look-alikes out there, but be forewarned there's a reason these are the gold standard. Once you dial these in to your desired air pressure setting, use a couple sets of pliers to really lock them in so they don't move position over time. Also, don't drop them in the dirt or the valve could stick, leaving you with a flatter than desired tire.
Manual Tire Deflator Tool
Brand: 23 Zero USA
Model: 4X4 RAPID TIRE DEFLATOR WITH GAUGE
This is also a great tool for airing down when we want to really dial in the pressure settings for a non-typical terrain. It is obviously more labor intensive than the auto-deflators but necessary for when you need custom PSI.
Model: CKMTA12 On-Board Twin High Performance Air Compressor
The ARB Dual Air Compressor is simply the best unit on the market when you consider the size, output, and performance. Save yourself some headache and start with the best. You can run air tools with this unit especially if you back it up with a reserve tank (below). We have aired up nearly 3 rigs in the time it takes some of the cheaper units to air up a single rig. This unit is an absolute work horse and will not disappoint.
Model: 171302 Inflation Accessory Kit
All air hoses might look the same, but make sure you go with one that can handle high temps, especially if you plan on mounting your compressor in your engine bay (many do, but we don't recommend it). This ARB hose has served us well and shows no signs of stopping.
Model: 250 PSI
Our previous air-up tool was made by ARB but recently failed us when the trigger mechinism failed and the pressure gauge no longer read correctly. Not too bad for about 4 years but this time around we are trying the budget digital version and so far it's paying off. The built-in gauge on this unit is extremely accurate for now and it seems to have a sturdy design. The company has actually contacted me twice to ensure it is working correctly. It's still early in its testing but so far we are liking its performance.
Inflator Tool Chuck Upgrade
Brand: Coilhose Pneumatics
Model: CH15 Closed Lock-On Chuck, 1/4-Inch FPT
This little gem was discovered after hours of searching the deep, dark shelves of Amazon. While this looks like a regular air-chuck, it actually has TWO opposing teeth to grip the valve stem when airing up as opposed to the standard single sided tooth that comes standard on every air-up tool out there. Slip this bad-boy on and there will be no air leaks while you're airing up for the 100th time and your valve stems are starting to wear from the clamping effect. This part is a straight swap for the above air-tool's chuck.
Model: 150 PSI
You're going to need a good air gauge to confirm your settings from time to time. Our older Craftsman unit does a steller job, but the Amazon reviews aren't so great on the new units. Enter the replacement... the reviews on this guy are impressive so it would be our next go-to.
Model: 2.5 Gallon
While not necessary with the incredible output of the dual ARB unit compressor, this tank has really upped our game with speed of fill and ability to run air-tools a bit more continuously. Nothing fancy here, just increasing your capacity and speed.
A slick little set of fittings for the above air tank. Note the safety valve... a good thing to have.
Tire Repair Kit
Model: 10000010 Orange Speedy Seal Tire Repair Kit
We recently had a piece of steel go through our trailer tire in the middle of Alaska and we were relieved to have this in the arsenal. We've also fixed our fair share of other folk's rigs with this kit. If you've ever used a plug kit, you know that a cheap insertion tool is recipe for busted knuckles. Not with these beefy guys! We also love that plug pusher mechanism which keeps you from pulling the plug out by allowing you to push the plug while pulling the tool. Fancy.