RV RV Tires

Viair 400p-RV and Jaco Inflator

Greetings RV enthusiasts .  With no automatic Tire Pressure Monitoring System (TPMS) for my trailer tires (yet) I had to come up with a solution to accomplish both adjusting and accurately measuring air pressure. My 4400-lb rated “super G” trailer tires work at 110psi (cold), so it was time for a serious but portable solution capable of operating at those pressures.


I was pleased to find the Viair 400P-RV portable compressor (available on Amazon), as it meets all my requirements.  It even fits behind the rear seat of my Mega Cab. This automatic unit behaves just like a larger compressor: Utilizing a hand-held inflator, the pump starts up automatically to keep up with the demand for air — just the ticket when using the supplied, 60 feet of hose! Power comes from large alligator clips that connect directly to the truck’s batteries . No ordinary, fused 12v source will do: This unit can draw up to 30 Amps!

Compressor Performance

Having such a compressor is also great for adjusting my truck’s tire pressures: When running empty, I fill my rear tires to 65 psi, and the fronts to 75 psi – to achieve a bit better ride comfort. When I’m getting ready to haul or tow, I can quickly bring all four tires back up to 80 psi.

When y0u get tired of those weenie little compressors sold at auto parts stores, you start looking at the performance specs that matter:  How much air can the compressor push while working at the expected tire pressures?   That means ignore the “cubic feet per minute” spec published by most compressor manufacturers, because that is probably specified at zero psi — thats right, zero!  unless you are filling up a child’s pool toy that just doesn’t do it.

Here’s the performance specs published by Viair, for the 440P-RV compressor at the pressures of interest to me .  First is my Truck’s tire pressures — 80psi, required to meet its axle requirements

At 80 psi, the Viair 400P-RV will push 1.37 cubic feet per minute.  Impressive.  no wonder my tires inflate from 65 to 80 psi in such a short time.    Well if that is not enough, consider my trailer’s “super-G”, 4400 lb rated tires, mentioned above — they require 110 psi (cold) in order to support that much weight, and the 400P-RV is up to this task as well.

At 100psi, the 400P-R  will push 1.11 cubic feet per minute!  It turns out I don’t need anything above 110psi, but the Viair is designed to work even harder than that:  at 150psi, it will push .71 cubic feet per minute!


To advantage quick and accurate air pressure checks, I replaced the Viair-supplied inflator with a Jaco, 200 psi digital inflator, seen in the photograph below.  The Jaco is just a better product than the inflator supplied with the Viair and performs double duty, both as a traditional inflator, and as an accurate stand-alone tire pressure gauge.  Without dragging an air hose around with me, I can check all of my trailer tires in a matter of 1-2 minutes

The other reason I chose the Jaco inflator is because I like its Lightening® valve stem chuck, which locks onto the valve stem without having to turn any threads. In the photograph below, notice the difference between the Jaco chuck (left) and the standard Viair threaded chuck (right). This makes the Jaco much more convenient to use.

happy pressures,


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