Section 4: Airing Down/Up
“Airing Down is essential when offroading.”
Why we Air Down
When we are just driving around town, on paved streets, our normal tire pressure is approximately 36 psi, give or take a few pounds depending on our specific tires and vehicle weight.
But as soon as we leave the asphalt and begin our offroad adventure on less civilized surfaces -- such as dirt, gravel, sand, stones, rock – we deflate our AT/MT tires to approximately 15-20 psi. Most of us aim to get closer to 15-16, but the main thing is to get below 20.
There are three main reasons for airing down.
1) It will soften the ride and greatly reduce getting bounced around in the passenger compartment. Imagine dribbling a basketball. Fully inflated, the ball has a lot of bounce. Let half of the air out, and the ball simply goes splat when it hits the ground.
2) Deflating the tire increases the tread footprint for much greater traction. Think of a tank or bulldozer caterpillar tread wrapping itself over obstacles, maximizing the contact area even over oddly shaped hard obstacles. In the case of sand, mud, or snow – this increased and flexible traction helps prevent getting stuck.
3) Less internal air pressure will reduce the risk of a puncture. Picture a balloon, fully inflated. Touch it slightly with a sharp object, and it pops. But grab a semi deflated balloon, and you could poke a pencil inches into it without it bursting. The balloon wall simply envelops a sharp object.
Many of you are nervous about the concept of driving around on “flat” tires. The low tire pressure warning light is flashing in your dashboard, and you remember your high school driving instructor telling you about all the bad things that could happen to you. Well, your instructor was right… it is not good to be driving around at high speed on a flat “street” tire. However, these are heavy duty AT/MT offroad tires and are built a lot stronger. Also, you are not cruising at 55-75 mph on the freeway but crawling at 5 or 10 mph along nature’s trail.
Sometimes we do drive along paved highways a brief distance in between adjoining trails. It is okay to remain aired down on these hard roads, just so long as you keep your speed within the 35-45 range. 55+ is not a good idea. If you were in 4wd on the dirt, don’t forget to shift back into 2wd while on hard roads.
Tools for Airing Down
Sure, you could just poke the end of a key against the springy valve stem core and let the air hiss out, stopping now and then check it with a tire pressure gauge. But there are much easier ways.
Types of DEFLATORS
The least expensive way to air down is with a deflator tool that is available at all auto parts shops and online. This consists of a gauge attached to a short hose. The end of the hose screws onto your valve stem. The rod that protrudes is then pressed inward and is used to unscrew and remove the internal valve core, which releases air quickly. Use the gauge to monitor tire pressure until you reach the desired psi. Replace the valve core. Then do the other tires. Be sure to keep a package of spare valve cores with you; sometimes one may spring loose into oblivion.
These are fast and efficient systems, but they do require continuous attention and remaining kneeled at each tire. You never want to leave these unattended.
Some offroaders praise them for their speed; others loathe them for having to unseat/reseat the valve cores every use. It is also very easy to mis-time your pressure checks, and end up lowering your tire pressure too much.
Avid air compressor from Amazon.
In the (likely) event that you deflate too much pressure, you will need to “air-up” that particular tire to your intended psi. Usually that means having to set up your 12v air compressor. But before you drag out that beast and clamp to your battery, there are some easier options. This is the right time to just use a compact, rechargeable (emergency roadside) small air compressor. Yep, the ones we tell you NOT to use for airing up all four of your offroad tires! But for just adding a few psi to one tire… they do the trick. We keep a handheld unit that we picked up on Amazon for around $60 just for that reason. If you do not have a little compressor, ASK the others in the group. Odds are that someone carries one of these, and it will save you a lot of time and effort for just topping off a few psi in one tire.
AUTOMATIC deflators
There are more expensive devices, known as AUTOMATIC DEFLATORS, that can be set to stop at a preset psi.
The most common system for deflating is to use a set of small, adjustable nodules that you simply screw onto each valve stem. These devices have a ring that can be set or calibrated to stop at a specific psi. You just walk around the car, attach to each valve stem, and then just wait for air to stop hissing out. Remove the devices, and you are done.
Speed chucks are press-on rather than screw on for connecting deflators or air compressors.
TIP: Save yourself from having to screw on these individual deflators by purchasing a set of “speed chucks” that allow you to just push & clamp onto the tire valve stems instead of threading them on.
Basic deflators, such as the Staun and imitators, require you to calibrate them. To do this, you manually get the psi in one tire to where you want it, using a handheld tire gauge (or reading the tire pressure off of your dashboard). Then, attach the deflator, and turn the ring until you feel some air hissing. Back off the ring a partial twist until the hissing stops – and lock the ring in place. Repeat this process for all four of your deflators.
We recommend using a marker paint pen to denote the setting, in case the locking ring loosens and the system rotates.
The original Stauns are considered very robust and generally accurate. A set of four, though, will set you back close to a $100. Available on Amazon. You will find a lot of less expensive imitators, starting at around $40. You get what you pay for. Don’t go the cheapie route; you will be sorry later. If the price is too good to pass up, then definitely pass up! Expect to spend at least $80-100 for a good set of deflators.
Laser engraved
Some brands of these deflators (such as J.T. Brooks) are laser engraved with psi; so you can more accurately set your deflators without as much fuss. The main issue that we have found is that the engraving is in 5 or 10 psi increments, so you have to guess (or do trial and error) to figure out any in-between values. For example, we set our J.T. Brooks at 15 psi (engraved) and then give it one additional revolution to bring it up to 17 psi.
Our biggest complaint with the J.T. Brooks style is that they are considerably slower than the Staun style. Originally, it did not make a difference to us that the Brooks style took a lot longer to air down, since we had to wait for everyone in the group anyway. But when we began being Trail Leaders, it became more important to us to finish up quickly, so that we could assist others.
Staun has listened to its users and also offers a premium version of its classic deflator that does feature laser engraving and indicator points on its body. But these units do sell for a higher price (around $140).
Over-Sand deflators feature engraved calibration settings.
Another engraved deflation system is sold by Over-Sand. This system allows you to dial in a base psi interval by lining up vertical and horizontal markings, and then fine tuning a plus or minus adjustment to achieve whatever psi you want (or to compensate for minor errors in each unit). After we have double checked the engraved calibrations against our tire gauge, we add a tiny label to indicate any +/- fudge factor.
Understand that these small tire deflators are only a combination of machined metal and a spring, so there might be is a psi discrepancy from unit to unit.
Multi-tire HOSE systems
Some people have invested in a quad hose system that connects to all four tires simultaneously with a central gauge/compressor that can be used to deflate or inflate all four tires at once.
Some offroaders use an octopus-like hose system to connect all four tires to a central hub in order to expedite airing down/up. These systems usually consist of two hose bundles, configured like an F. The hose for each side of the vehicle connects to the front & rear tires on its respective side. The two hoses then join onto a central Y adapter that is equipped with a tire gauge and airflow controller. To air down, you simply switch the controller to release air. Stop it periodically to read the gauge, and then proceed again to release air. Because all four tires are connected simultaneously, the theory is that the overall tire pressure is all tires will equalize as they deflate (or inflate from an air compressor).
Like everything else in offroading, there are those who love it and those who can live without it. You do gain a lot of speed in being able to deflate four at a time, and usually all four tires will have similar psi. On the flip side, it does require storing, untangling, setting up, and then re-packing a lot of hose and your central hub. Is it better? Or just a pain?
Do NOT rush out and buy anything yet!!
There are many tire deflator systems out there, so shop around and see what works for your budget. I would recommend going out on a trail run with a local offroading club so that you can see and try out different brands. Fellow offroaders will assist you on your first couple of runs, show you what to do, and let you try out various solutions.
Don’t forget to purchase a good, digital tire gauge. There are some excellent digital ones on Amazon for under ten dollars.
Another useful tip:
“Most of your modern SUV’s have a dashboard setting to display individual tire pressures. Use it to monitor the progress of your air down and air up. In our Sahara, my TPM (tire pressure monitor) is accurate enough that I almost never need my handheld gauge.”
Airing Up
At the conclusion of the trail run, we will air our tires back up to normal street pressure, which is usually around 36 psi (but could be 33-38 psi). However, it depends on your specific tires and vehicle weight.
Airing up at the end of the run.
Short of driving to a nearby gas station (not really practical), here are your sources of air for re-inflating the tires.
The most common source is to use a portable 12v air compressor that you remove from the vehicle, hook up to your battery (engine running), and connect a hose.
Some offroaders have on-board mounted air compressors, so that they only need to connect their air hose.
Hardcore offroaders may carry a compressed air tank. The tank is high pressure, so it fills the tire very quickly; but it is bulky.
Sometimes you will see offroaders equipped with quad-hose systems. Instead of a single air hose that does one tire at a time, quad-hose systems octopus out into all four tires simultaneously.
Smittybilt #2781 air compressor
Here is an example of a Smittybilt (model #2781)12v, 5.6 cfm air compressor. Note that it has a thicker power cord with clip-on battery leads for connecting directly to your vehicle battery. Besides Smittybilt, there are several major manufacturers such as ARB, Viair, Morrflate, All Top, and others – so ask and shop around. Make sure that the compressor is rated at least 5.6 cfm or higher, or else it will take a long time to do all four tires.
This “roadside emergency” air compressor is only 1.25 CFM
Here is an example of what NOT to get. This is for emergency roadside use: putting a few pounds of air into a street tire. It is neither powerful nor heavy duty, and will take you a long time to reinflate four AT/MT big tires. The unit, besides being very slow, will overheat if you do not allow it to rest every 10 minutes or so.
The first giveaway that this is a light duty air compressor (maybe 1 cfm?) is the thinly corded 12v CIG plug, which means that it does not draw very much current.
A stronger air compressor will draw more amps, and needs to be directly connected to your battery by clipping onto the battery terminals. Make sure to keep the engine running, or you will suck your battery dry.
Useful time-saver
• When airing up or even airing down – have your passenger monitor your tire pressures using your dashboard display.
• Ask them to signal you or honk the horn when each tire achieves the desired psi.
• Some jeeps come equipped with Tire Fill Assist, under Settings, which honks when each tire reaches 36 psi
Some of the newer air compressors feature built-in digital controllers (not to be confused with digital tire gauge). These controllers allow you to pre-set a target psi, and then the unit will pump air until this target is achieved, and then stop. This is a definite game-changer in terms of convenience. You are no longer a slave to a handheld gauge or staring at your dashboard. Set it, forget it.
Also, these new compressors are dual cylinder and much more powerful (faster) than the older 5.6 CFM. We just purchased an All Top rated at 12.35 CFM, which inflates our big offroad 35-inch tires in a fraction of the time. They are actually very close in size and weight to most of the 5.6 units, and only moderately more expensive. We got our Smitty back in 2021, but technology has improved.
Some of the popular digital compressors include Thor”s Lightning, Morrflate, and All Top. But there are lots of brand names out there, with many companies just white labeling similar units from just a few OEM factories. Do a little internet research.
These more robust air compressors also offer optional multi-tire hose systems (as described above). Do not rush out and purchase a hose system until you have played with them on the trail. You can buy generic hose systems from many vendors that will be compatible; you do not need to spend big bucks to match the brand of your compressor. Fittings are pretty standard for most compressors, but some brands (such as Smittybilt) do use a proprietary fitting.
No worries…
we got you covered!
When you join a Beginners Trail Run, don’t be concerned that you might not have proper deflators or an air compressor, or know how to use them.
Offroaders are a friendly, helpful community.
We will bring over our equipment and teach you how to air down or air up.
No one gets left behind. Trail Leaders and Trail Staff will not leave the Trail finish area until everyone is aired up and good to go.
