Onboard air is one of the most useful accessories you can add to your 4×4. You can buy a new Jeep or truck with locking differentials and all-terrain tires, but no vehicle currently comes from the factory with onboard air. That’s ok though because the aftermarket has plenty of options to help you air your tires back up at the end of the trail. You are airing down off-road, right? We have advocated the benefits of airing down in the past, whether you are rockcrawling or traveling over miles of washboard roads. Onboard air has plenty of other uses though as well, from engaging air lockers to airing up your mattress or blowing dust out of your rig. Larger tasks like reseating a tire bead or running air tools won’t be possible with a cheap compressor you plug into your cigarette lighter. There are several different specifications to consider when purchasing an air compressor.
Cubic Feet Per Minute (CFM)
CFM is a measure of a compressor’s flow rate, or the amount of air that a compressor can produce at a given pressure. CFM is often expressed at a given pressure. Compressors boasting big CFM numbers at low PSI are good for things like air mattresses and soccer balls, but they slow down significantly at the pressure required for filling a tire. Flow rate is also important for things like running air tools, which typically require 3-5 CFM to operate. You might not want to bring your Snap-On air gun on the trail, and we can’t say we blame you, but efficiency is one of the biggest benefits to high end air tools over their cheaper counterparts.
Duty Cycle
Duty cycle is the amount of time a compressor can be running versus the amount of time it needs to cool down to prevent overheating, typically for a given hour. For example, a system with a 100% duty cycle can run continuously at a specified pressure and temperature, where a compressor with a 50% duty cycle will operate only half of that time under the same conditions. A lower duty cycle isn’t always a bad thing though, as many compressors with lower duty cycles flow a higher CFM. Think of it like a sprinter versus a marathon runner. Small tires can be filled in a sprint, but if you are running 37s or 40s, duty cycle becomes more of a concern. Quality compressors, such as those from ARB and Viair, are equipped with a thermal overload switch that will automatically shut the compressor off until it cools down to prevent damage.
Portable or Hard Mount?
Another factor is what compressor to purchase is whether you want a unit that is portable or hard mounted to your vehicle. Both have their advantages, depending on your specific needs. If you have multiple vehicles, or don’t want to deal with the complexity of hard wiring a compressor, a portable unit is likely a better choice for you. A permanently mounted compressor can be placed under the hood though where it doesn’t take up valuable storage space, and hard wiring provides a better connection to the charging system for the high amperage demand of air compressors. Hard mounting the compressor also allows you to add a storage tank, which provides a reserve that useful when running air lockers, reseating a bead, or loosening hardware with an air gun.
Construction
Of course, even the most powerful air compressor won’t do you much good if it cannot withstand the rigors of off-road use. Look for a compressor constructed with high-quality components and the ability to be serviced in the field, if necessary. Features to seek out include thermal protection, as noted above, and vibration resistance, such as the use of rubber mounting feet. You also want a compressor that is sealed from dust and water resistant, preferably with an Ingress Protection (IP) rating, such as IP55. The first number refers to the intrusion of things like dust and dirt, while the second number refers to liquids. The higher the numbers, the better sealed the compressor is.
What Else You Need
Before you can air up your tires you will need to add a gauge and hose. Analog gauges tend to be less expensive than digital gauges, and we prefer gauges that have a locking chuck that stays on the valve stem without having to hold it the entire time. Many kits come with coiled hoses, but if our experience a flat hose actually takes up less storage space when it is not being used since it packs flat. For drivers looking for a complete on-board air solution, ARB is offering air compressor kits with everything you need under one part-number. They are available with a single-motor or twin-motor compressor, and include an air up gauge, hose, manifold, all wiring, and universal mounting bracket in addition to the compressor. Of course, these parts can be sourced individually as well if you say, don’t need the manifold to engage your air lockers, or want to use a vehicle-specific bracket for the compressor.
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