By all measures, the most effective (and most expensive) is the converted air condition pump used to provide high volume air. The market leader for these is Kilby On-Board Air providing a complete system for about $1200.
The CO2 tank, popularized by PowerTank, are effective and relatively inexpensive. Power Tank is the original high performance CO2 air system for offroad use. I have used one for a number of years with satisfactory results. Yes, the regulator can “ice-up” and, yes, you need to periodically re-fill the tank. And, in my case, space to mount the tank and carry a load of camping equipment was becoming a problem.
That opens the look for on-board air to the variety of offerings in the 12 volt compressor category. Early innovation in the 12 volt compressor market started with Sun Performance and the Quick Air. The Quick Air 4x4 compressors are noted for high output and low current draw for reliable on-board air.
As tires became larger, bigger compressors were required and other providers have entered the market. The 12 volt compressors feature compact size requiring minimal space, and oil-less design permitting mounting in any position and any location (as long as it is a dry location). They can be used with or without external air tanks.
Two vendors provide compressors that are billed to answer the need to fill larger tires: MaxAir 4.0 from 4WD Products and Viair 450C.
The MaxAir 4.0 is a portable unit weighing in at a hefty 30 pounds comes in a 18.5x10.5x6 inch metal case. The compressor provides 4.0 CFM airflow with a maximum pressure of 150 PSI.
The Viair 450C is a hard-mount unit. The compressor provides 2.68 CFM airflow with a maximum pressure of 150 PSI.
Looking to recoup space inside my jeep by replacing the CO2 tank with a compact compressor, I picked up the Viair Constant Duty Onboard Air System featuring the 450C compressor and a 2.5 gallon tank.
Install started with challenges. The first order of business was where to mount the compressor. While “under the hood” is a common location, I opted for an in-side mounting solution, specifically on the floor behind the drivers seat. The entailed an extra length power cable was required, about eight feet of 8 AWG wire.
Compressor location decided, I began searching for a mountain location for the air tank. It quickly became obvious that the 2.5 gallon tank was not going to work for my needs as an interior mounting solution would have required more space than the CO2 tanks and underneath mounting would have severely reduced ground clearance.
Unwilling to concede defeat, I resurrected a one gallon air tank used in a previous install with a Quick Air unit. The smaller tank allowed for installation suspended underneath the jeep between the driveshaft and the driver side rear springs. It sits higher than the frame rail and almost above the rear axle, well out of harms way.
The leader hose from the compressor was long enough to reach a T-block from which an additional line was extended to provide the connection for the air hose. Again, reaching under the workbench, I pulled out a 25 foot length of 3/8 ID air hose and a quick trip to the local tool store yielded some hose repair pieces providing 1/4 NPT fittings. Cutting the hose to length a quick-disconnect coupling is now mounted on the rear of the jeep next to the tail-light. Again, it is high and protected from external damage.
For the compressor mounting location, I fashioned a protective bracket that will keep things from sliding down on top of the compressor. The 450C features a pressure controlled on-off switch as well as a dash mounted switch and pressure gage. The protective bracket also is the mounting for the pressure switch.
Overall, the install was more complex than indicated by the instructions. And, kit appears to miss a key installation item. There are two power connections; one for the direct power to the compressor and the second, a control switch to the pressure controller. And, only one fuse holder was provided. It was easy to find an unused terminal on the under-dash fuse block controlled by the ignition switch. I do not like to run extended power lines without a fuse. That meant I needed a fuse holder for the control switch and a fuse holder for the power line.
Another drawback with the kit revolves around the size of the air tank. In most install situations, the size should be no problem. However, if you are concerned about space, the tank is too large for use.
Another downside is the number of air hose taps required to the tank. As provided, the Viair is tapped for six connections. One connection is for a drain plug and another for a safety pressure valve, leaving four for other connections. The pressure regulator and gage should be on a separate tap. In my case, I was able to run a single line to a T-connection to provide a connection for the pressure switch and pressure gage. From a second tank tap, I was able to mount a T-connection to provide input to the tank and output from the tank.
If the provided tank were used, there would be several air lines looped out that would be tempting snag attractions. The provided plastic air line is stiff and does not conform to tight, snag free bundling. That is more of detriment to the use of plastic air line for installs. Rubber hose and a variety of NPT fittings exist to provide for snag-free installations. While elbow fittings are available for the 1/4 inch plastic line, I have a prejudice against plastic line.
With the installation and operational test complete, I performed a couple of simple timed tire inflation tests. The test tire was mounted to the jeep (295/75R16) deflated to 15 PSI.
The first test was using the Viair to inflate the tire from 15 PSI to 35 PSI. The second test was to use the MaxAir 4.0 to inflate the tire from 15 PSI to 35 PSI.
And, the results are in with the MaxAir taking about 30 seconds less to complete the task. The Viair inflation time was 3 minutes 55 seconds. The MaxAir inflation time was 3 minutes 25 seconds.
Overall, the difference is negligible and should not be an issue. If you are considering an on-board air system, consider your situation and available mounting configurations.
The compressor needs to be installed in a dust and moisture protected area. Keep plastic air line away from heat and sharp corners. Keep power supple lines away from sharp corners and edges.
Overall, I consider space a primary factor to consider. The less space used by the install, the better. Tire size is a consideration and your selected compressor needs to accommodate the size of tire installed. While being able to seat a tire bead or run air tools is a positive feature, they do come with a trade-off.
Both compressors I tested are sufficient to inflate up to 37 inch tires.
Shop around for features that meet your needs and price that fits your budget.