One of the most critical pieces of gear for off-roading and overlanding is an off-road air compressor for refilling your tires. The ability to refill your tires after airing down, whether voluntarily or involuntarily (a.k.a, “a flat”), is one of the pillars of being safe and having fun off road. Many owners of Jeeps, Land Cruisers, Broncos, Tacomas and other SUVs and trucks will also adjust their air pressure on the trail depending on the terrain.
This guide will explain the different types of off-road air compressors, how they are used, and offers some tips on choosing the right compressor for your needs.
Uses of Off-Road Air Compressors
Air compressors used while off roading have two tire-related purposes. The most common use comes after you deflate tires to improve traction, prevent tire damage and soften the ride for you and your passengers while on the trail. In that case, you use the air compressor to reinflate the tires when leaving the trail for the pavement or adjust mid-trail to adapt to changing terrain. The other primary use of an off-road air compressor for tires is reinflating a tire you’ve repaired on the trail–for instance, when you’ve damaged two tires and you’ve only got one spare.
Some air compressors can also be used for powering axle differential lockers and air tools, which we’ll get into more below.
Off-Road Air Compressor Types
There two common types of tire-inflating air compressors, on-board and portable. A third option, popular among offroad racers and hardcore wheelers, are portable air tanks filled with CO2 or nitrogen that rapidly inflate a tire, as the gas expands quickly.
On-board Air Compressors
On-board air compressors are mounted to your vehicle, in the engine bay or somewhere else on your vehicle and remain wired to the battery. On-board air compressors offer conveinience, as they are already connected and ready to go when you need them. They also typically serve multiple purposes, as on-board air compressors also power pnuematic control for air-lockers for differentials in axles. Larger onboard compressors can also power air tools, such as air impact wrenches for removing wheel lugs.
Typically, when an on-board system is installed, switches are integrated into the dash or somewhere else on the vehicle so the differentials can be locked from inside the cab. No more climbing out and twisting the hub on the wheels like in the olden days.
- Pros: Convenience on the trail; multiple uses, including powering air lockers and tools
- Cons: High cost of initial installation; might not fit some engine bays without modifications; upgrades and repairs to compressor are more costly/time consuming
Portable Off-Road Air Compressors
Portable off-road compressors are carried in a bag or case that you take in and out of your vehicle as needed and are clipped to the battery terminals when needed. Smaller models can often plug into cigarette lighter ports, but these models may be too small for larger truck tires. Portable air compressors offer more flexibility than on-board units, as you can move them between vehicles. You can also move them around (as far as the battery clip wires will allow) so you don’t have to stretch the air hose so far to reach the tire valves. That said, each time you use a portable air compressor unit, you have to unpack it, connected it to the battery, let it cool down and then pack it back up. It’s more hassle and eats into trail time.
- Pros: Relatively inexpensive; no installation required; flexibility to move unit around
- Cons: Hassle to unpack, use and pack backup; another thing to remember to pack; takes up room inside vehicle
Portable CO2 and Nitrogen Tanks
Portable tanks filled with carbon dioxide or nitrogen look like something a SCUBA diver would wear on their back (don’t try breathing out of them!). These tanks offer rapid inflation, as these gases can be compressed more than oxygen in the tank but expand greatly when put into a tire.
If you are going offroad quite a bit or have large tires that take a long time to fill, these can really help you save time. However, the amount of gas in the tank is finite, and so you’ll still want to bring along a compressor that powered by your engine’s battery as a backup.
- Pros: Rapid tire inflation saves time on trail; fill large tires (35 inches +) more easily
- Cons: High cost, especially since you’ll need another air compressor as well; finite number of tire inflations; needs to be refilled, which requires time and money; large tanks take up space in car and add cargo weight
Off-ROad Air Compressor Features
Here’s an overview of the various parts of an air compressor. I’ve include some of the ratings such as pressure, duty cylce and air flow, that you can use to determine which one will suit your vehicle and needs as well as provide guidance on how to use.
Parts of an Air Compressor
Air compressors typically have these key parts:
On reciprocating air compressors, the type used in off-roading, the motor powers the piston in the compression mechanism.
In the compression mechanism, a valve allows air to be drawn into a cylinder. A piston then forces that air through the air hose an into the tire. This cycle repeats until your tire is inflated.
The air hose carries air from the compressor to the tire. It’s important to get a long enough air hose that you can reach all of the tires on your car when your air compressor is connected to the battery or cigarette outlet.
The tire chuck is the part of the compressor that connects to the valve stem of your tires. For compressors used in off-roading, it’s recommended that the chuck have a built in deflator and inline pressure gauge.
The power cord or wiring (in the case of an onboard model) connects the compressor to a power source, whether it’s directly the vehicle’s battery or through a cigarette outlet.
Air Compressor Ratings
Compressors used for off-roading are typically rated according the following parameters:
Tire size: Some manufactures do the math for you and tell you what model compressor is good for a given tire size. Typically, this comes down to the compresssor’s air flow capacity (measured as CFM), which is explained below.
Pounds per square inch (PSI): The force of air that the compressor can deliver. PSI is particularly important for running air tools, but most off-road air compressors deliver plenty of pressure to inflate truck tires, so PSI isn’t much of a consideration.
Cubic feet per minute (CFM): The air volume the compressor can supply per minute. CPM tells you how fast a compressor can inflate a tire while running–with run time depending on duty cycle (see below). Having a high-enough CFM is really important for inflating large truck tires, and high CFM compressors will speed up inflation of any tire.
Duty cycle: Compressors alternate on/off cycles to give the compressor engine a break and prevent overheating. The ratio of on-to-off time required during a 1-hour cycle is the duty cycle rating. For instance, a compressor with a 50% duty cycle can run for 30 minutes during an hour. In hot weather, the cool down time will increase, as the compressor will heat up faster.
Voltage: Air compressors used in off-roading are typically either 12 or 24 volt models. Larger comoressors require higher voltage and deliver higher air flow and pressure.
For inflating tires for off-roading, a tire size rating (if available) is the handiest measure for deciding what compressor to buy. If a straight forward tire-size guide isn’t available, use the other ratings to choose the right machine for your needs.
This table shows a few popular portable compressors as examples of different ratings and tire sizes:
|Viair 440P Portable Compressor|
$260 on Amazon
Duty cycle: 20 minutes/hour
|Up to 37″ tires|
|Smittybilt 2780 Universal Air Compressor|
$93 on Amazon
Duty cycle: 40 minutes/hour
|Up to 35″ tires|
|VIAIR 300P Portable Compressor|
$152 on Amazon
Duty cycle: 35 minutes/hour
|Up to 33″ tires|
How to Choose an Off-road Air Compressor
On-board or portable?
Whether you choose an on-board or portable compressor may come down to whether you have air lockers on your axle differential. If you do have air lockers or are planning to install them, it’s probably worth getting a large enough air compressor unit that you can also use it for tire inflation.
Other pros, cons and considerations are outlined above, in the section on the two types of compressors. In my opinion, if you don’t have air lockers, a portable compressor is more flexible and cheaper option than going through the hassle and cost of installing an on-board unit.
How big are your tires?
The volume required to inflate your tires will set some basic parameters around your choice of an air compressor. You’ll die from boredom waiting for an underpowered air compressor to inflate a large off-road tire (say, anything 33″ or bigger). Also, a smaller off-road compressor will not have the engine power to pump up a large tire.
Manufacturers typically offer guidance on which models of their off-road air compressors are good for different sized tires. Models appropriate for larger truck tires typically connect directly to vehicle battery terminals and don’t plug into cigarette lighter outlet (are we still calling them that?), as the outlets aren’t rated for high enough amperage. Check your outlet rating to find out how much amperage it can handle.
But, really, how patient are you?
More powerful compressors push larger volumes of air per minute, hence filling tires more quickly. Put simply, the faster you want to air up, the more powerful the air compressor you should get. If you really want to speed up the process, consider a pre-filled CO2 or nitrogen tank system.
A number of companies make portable air compressors well suited for off-roading and overlanding.
At the high-end, the Australian company ARB makes on-board and portable off-road air compressors that are considered the gold standard. You’ll pay for quality. A bit more affordable, California-based VIAIR also makes both on-board and portable compressors, and offers a wide range of models. These are solid machines for a reasonable price.
If you’re looking for a budget option, Smittybilt, also based in California, makes two portable compressor models (along with everything else under the sun). Smittybilt makes a lot of stuff, so this isn’t a specialty for them. You get what you pay for, but if you’re not putting your compressor under heavy use, these might be just fine.
Does it have a deflation mechanism?
Airing down your tires can also take time. Fortunately, a number of air compressor valve chucks come with built in mechanisms that will release the air from the tire without you having to stand there holding down the valve stem. These are definitely worth having. That said, some tire gauges come with this as well, and you could buy one of those separately for airing down. We actually own an extra tire gauge that locks open so that two tires can be deflated at once.