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By: Brian Goley

ATV enthusiasts who often travel to OHV Parks, their favorite sand dunes, or down to their local riding spot sometimes need a source of compressed air. Especially those off-roaders who need to traverse across sand with their ATV haulers or tow vehicles with trailers and have to air down their tires for adequate traction.

ATVers have a variety of needs for an air compressor during their outings. From airing up deflated truck tires, fixing ATV flats, or wherever a quick shot of air or a lengthy pump up is required, Viair Corporation of Laguna Hills, California, offers a wide selection of heavy duty, hard mounted and portable air compressors to save the day.

Viair 400P Air Compressor Kit

Viair asked us to evaluate their most powerful portable compressor. Viair's model 400P is a must have piece of equipment because of its portability, compact size, sturdy construction and ratings that should enable it to handle most, if not all, of your air compressor needs. The 400P kit comes with a heavy duty water and dust resistant double compartment carrying bag. The entire kit is a small 11.25 × 4 × 7 inch package that weighs in at only 8.50 LBS and can be easily stowed away.

The 400P compressor has a gearless direct drive 1/4 HP motor, a thermal overload protector with an automatic reset switch, and it is also moisture and dust resistant. It uses an anodized aluminum alloy cylinder, hi performance PTFE or Teflon piston rings and stainless steel valves that provides for a long life of robust and corrosion-resistant performance. The compressor comes with a dual element air filter, a 35 FT versatile coiled air hose with an inflation/deflation valve, a 2 inch diameter inline pressure gauge that measures up to 100 pounds per square inch (PSI) and a locking tire valve chuck that also allows for rapid deflation.

To provide power to the unit, an 8 FT power cable protected by a 30 amp inline fuse and battery terminal clamps, is provided. Powering the Viair from battery terminals rather than the cigarette lighter or 12 volt DC power receptacles provides considerably more air pressure. This makes it possible for the compressor to pump up larger tires such as those found on pickup trucks and many trailers. For optimum performance, the manufacturer recommends the engine of the vehicle be running when the compressor is in use.

The maximum reach from the battery source to the item you’re airing up or down is an impressive 43 FT. This should allow for easy reach to all tires on most vehicles and trailers.

Viair 400P Air Compressor Kit

We tested the unit by deflating the tires on our Expedition. The tires are P265/70R17 all-terrain tires which is a common tire size found on most ¾ ton pickups. We did this by attaching the locking air chuck to the tire’s valve stem and then simply pushing the system's inline deflator collar forward and locking it in place to allow continuous hands free air flow.

Viair's claims that the 400P should "air up a 31 × 10.5 inch tire from 15 to 30 PSI in about 1 minute and 25 seconds or from 0 to 30 PSI in about 2 minutes and 28 seconds."

Our tires measured in at 31.6 X 10.7 inches which is of an adequate size to test the unit. Inflating our tires from 0 to 35 PSI took 2 minutes and 25 seconds per, which seems to more than substantiate Viair’s claim. We tracked the air pressure via the inline gauge. For those ATVers who need to air down their tires when traversing sand, the Viair should be more than adequate to both deflate and re-inflate in less than 15 minutes. This includes the time required to hook up the power cord to the vehicle's battery.

We did notice that our PSI readings via the inline gauge were off by about 8 PSI when in operation. To get an adequate PSI reading, you need to stop inflation and then take a reading from the gauge. This seems to register an accurate measurement most of the time. So, to air up a tire with MAX PSI of 35 you should stop pumping air into the tire when the gauge reads 43 PSI. We validated our measured PSI using a Craftsmans 12V portable air compressor and a standard pencil tire gauge. Our 2 devices reported the same PSI on all tires while the Viair was a consistent 8 PSI more during operation and spot-on while powered off.

Viair 400P airing up our ATV tire

As you can read, airing up vehicle tires did not take long, so care should be taken when using the unit to inflate ATV tires. It takes only a matter of seconds to fully fill your standard ATV tire. We timed a 25 X 12 inch ATV tire from flat to full in less than 15 seconds.

When we wanted to hook the compressor to our Kawasaki Brute Force 750i, we found that the new Kawasaki has a protective case around the positive post on the battery. This didn’t allow us any way to connect the 400P’s positive cable without first removing the case which supports the battery by keeping it secure. Of course, a little modification will quickly remedy the situation, but we don’t really see the average ATVer taking this unit on a trail ride with them, but rather keeping and utilizing the unit at base camp or in their vehicle.

The 400P is rated with a maximum duty cycle of 40 minutes at 30 PSI, or 15 minutes at 100 PSI at 72° F. At 30 PSI, the unit delivers 1.77 cubic feet per minute (CFM). Most reasonable inflation needs should not present a problem with overheating. If it does, its internal thermal protection circuit will automatically shut the system down and reset itself. The average wait for further use is approximately 30 minutes.

All Viair compressors are covered by a limited warranty of one year when properly installed and under normal conditions of use. Coverage is limited to defects in workmanship and materials.

ATV Source has been utilizing the Viair 400P for 6 months now and it has proven itself to be a high performance quality product. We have used it to inflate ATV Tires, SUV tires, truck tires, portable swimming pools, small inflatable kid’s games and even on a bike tire. The unit has been flawless every time. We have set the unit on the ground, in the engine housing, and on the hood of some vehicles. The unit has a built in anti-vibration aluminum tray which keeps the unit from jumping around or burying itself in the sand during operation.

Having a portable compressor with you while out riding will make the difference between a great riding trip or a complete washout. We all know that tire pressure is the single most important factor affecting vehicle safety and performance that can be influenced by a driver. When it comes to maintaining safe inflation pressures for any type of on or off-road driving activity, you need a portable compressor that won’t let you down.

Contact info:

26072 Merit Circle, Ste. 111
Laguna Hills, CA 92653 USA
Toll Free: (800) 618-1994
Phone: (949) 582-6868
Fax: (949) 582-6866
Web Site:

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