Tell me, have you ever checked the accuracy of a new tire pressure gauge before using it?

Neither have I. That is, until I got a lesson.

Recently I initiated a test to determine if, as some anecdotal reports suggest, a tire filled with CO2 loses pressure more quickly than one filled with air (more on that in a later post). CO2 tanks are sometimes seen as an alternative to compressors—while finite in capacity, they are very fast and completely portable.

I used the front tires of our 110 as test subjects. I deflated both completely, then filled one to 40 PSI using a CO2 tank and the hose/trigger/gauge assembly I keep with the tank. I filled the other to the same pressure with the built-in ARB compressor on the JATAC, using its own hose/trigger/gauge.

I decided it would be smart to verify exactly equal pressure in each tire using a separate gauge, so I checked the air-filled tire with one of our Accu-Gauges—40 PSI on the dot. Then the CO2-filled tire—49 PSI.

Uh . . . what? I checked it again. Same result. I checked the tire with another AccuGauge—49 PSI. I checked it with a $2.99 plastic-bodied pen gauge—49 PSI. I put the CO2 tank’s gauge back on it—40 PSI. I checked the other tire which I knew to be at 40 PSI, and the CO2 tank’s gauge read 32 PSI.

I’d always assumed that consumer-grade pressure gauges could be off by a pound or two—immaterial in most situations. But 25 percent? That represents a potentially dangerous discrepancy. If, for example, I filled the E-range tires on our F350 to their maximum recommended pressure of 80 PSI before hauling a heavy load, they would be nearly 20 PSI over that if I used the faulty gauge. (I’m reminded here of a passage in Fear and Loathing in Las Vegas involving a Cadillac El Dorado . . .)

Suffice to say I’ll never again use a new gauge without checking it against at least a couple others.