There’s no doubt that airing down your tires when trail riding is the single biggest improvement you can make to not only the experience but also your capability.
The illustration below shows just how much the tread footprint is increased when airing down. Sure you will lose a bit of height, but I will take the 225% (or more) footprint increase over the lost 25% of tire height any day. To put this into perspective… a 35×12.50R17 tire has an approximate rolling radius of just over 17 inches at full operating pressure. Airing the tire down to 10 PSI drops the rolling radius to roughly 15” but your effective traction increases by 250%! But not only will traction improve, your tires will also clean out more effectively and the ride on the trail will be far more enjoyable as the tires can flex and absorb some of the bumps.
So, why do so many new off-roaders seem to skip the act of airing down their tires before trail time? Perhaps they think that you need bead locks to run aired down tires. While it is certainly true that the risk of separating a tire bead off the rim is greater when using a traditional wheel, there is still plenty of room to air down for increased traction before this becomes a real concern.
Another possible concern could be the ability to air them back up for the drive home. In fairness, it’s been quite some time since I considered airing up at a filling station as a reliable technique. Heck, most filling stations don’t even have an air station anymore and the ones that do are rarely operational.
The solution is on-board air. But don’t let this scare you…. While it is possible to spend lots of coin on a fancy system, there are many much less costly and just as effective solutions out there. Let’s go over some of them along with their pros and cons.
Before we dive in too deep it’s important to understand some of the terms and specifications of these systems to help you make a decision and better understand the differences:
Duty Cycle: Usually rated in a percentage, represents the amount of on time to off time the compressor can run. This is typically limited by the compressor’s ability to cool itself while in operation. A compressor with a 25% duty cycle will need 30 minutes of rest for every 10 minutes of operation. Running a compressor with a low duty cycle for extended periods of time could cause it to overheat and fail.
CFM: “Cubic Feet per Minute” is a measurement of the velocity at which air flows. A lower CFM rated compressor will take longer to fill tires than one with a higher CFM rating.
Amps: Short for ampere and is a unit of electric current. Most on-board air compressors have a DC electric motor. Larger CFM usually coincides with a larger motor which will draw more current. Higher current means more robust and heavier electrical connections.
With that out of the way, let’s talk about some systems.
Emergency/Portable Compressors (Typically <$40)
By far the most cost effective solution. This type of compressor is quite handy as they are small and most come in a nice case or bag. They typically have very small motors which allows for an electrical connection via the 12v accessory outlet in the vehicle. Along with that small motor is a small CFM rating. In fact, most don’t even give you an actual specification for this and instead offer “Tire fill up times”. Be careful with this however, as a larger off-road tire has much more volume than a traditional car tire. I have seen post trail fill-ups take as long as an hour with this type of compressor.
Another specification often missing from this type of compressor is duty cycle. This said, it is important to remember that they are intended for use in an emergency and not over-and-over. I would not count on this type of solution to last a long time but it is sufficient for a fill-up when another isn’t available.
Entry Level Compressor ($50-100)
What I consider to be the entry level of compressors offers many of the same advantages as the emergency type, but they are built more ruggedly and are backed by some actual specifications. They typically offer a 1.5-1.7 CFM which will fill a 31×10.50 tire in less than 5 minutes. This higher fill rate also means a bit more current is needed to supply the motor’s power and the 12v accessory plug is replaced with allocator clips that connect directly to the battery to suit this. Duty Cycle is still very low (usually 15%) so you may need to take a break to let the compressor cool between tires.
If you only go trail riding a few times a year, this may be all the compressor you will ever need.
Enthusiast Compressors ($120-250)
At about this price point you could be looking at permanently installing the compressor somewhere on your rig or still wanting to keep a portable solution. The compressors in this category have about the same feature sets either way with the main differences being in the accessories and duty cycle ratings. It is not too difficult to find a 100% duty cycle compressor at this price point. While these compressors often still have the 1.5-1.7CFM rating the increased duty cycle will get four 37s filled in less than 20 minutes.
High End Compressors (> $300)
If you are still looking for more, there are plenty of options out there. Whether you want to retain portability or install it permanently, the sky is the limit. Chances are that if you are looking for more it isn’t to fill tires. You may be looking to run air tools and/or air actuated lockers which means you will be looking to install a manifold and possibly an air tank.
When is it a good idea to add a tank? It depends on your needs. An air tank helps to regulate fluctuations in pressure caused by valves cycling (lockers). It also increases the available volume of air for air tools. Unless you are looking at a very large tank, it really will not help much with filling tires so evaluate your needs before adding one.
Another solution for filling tires and running tools is a compressed CO2 tank. This is exactly what it sounds like. A somewhat small tank of compressed CO2 (~2500PSI) giving you a massive amount of volume once it is regulated to an operating pressure. They do not use electric at all but once they are empty they are done. Fill-ups can be done at most welding supply shops for $15-$20. By now you are likely tired of reading my ramblings so check out the Powertank video below for more information.
Hopefully this information has helped take some of the intimidation out of selecting a tire fill solution. If you have any questions or comments, feel free to post up. We’d love to hear from you.