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Pressure Gauge Calibration

I check my tires weekly, using a digital pressure gauge. Here’s the problem: I recently got a new gauge and it reads about 10% different than my old one. One (or both) of these gauges is wrong. Anyone know how to calibrate a tire pressure gauge? I work in a place where most of our high-accuracy, high-precision devices are sent out to a NIST-certified lab for cal. I don’t want that kind of expense, just want to know if my gauge is OK.

If you don’t have the calibration tool, which NIST labs do, the only way is to compare against a known good gauge. There is likely no way to adjust your new digital gauge, though.

Similar to what I posted in another thread:
Carry a box of donuts to a shop and ask to compare your gauges to one or two of their best gauges.

What I do when I have a device that’s off by a known amount, and not practical to adjust, is put on a label with the correction factor.
For instance, I have a pencil gauge I keep in my glove compartment.
I have a label on it (made with a Brother P-Touch) that says “add 2”, so I know to add 2 psi to its reading.

I have a digital gauge (Radio Shack!) that agrees with the TPMS in the car, so I have high confidence in those.
That gauge only comes off the shelf to do comparisons a couple times a year.
Then, most of my tire checking is done with an Accu-Gage dial gauge that has drifted 3 psi over many years of being bumped about.
I could get a tool to pop off and re-seat the needle, but it’s not worth the bother IMHO.

You could compare against the gauges of your family and friends to get a better idea of which one is more likely to be correct.

I’ve heard that the analog dial-type gauges tend to be the most accurate, for what it’s worth. I have three such Accu-Gage gauges that all agree.

I use a bourdon tube tire pressure gauge.

image

It’s the most accurate tire gauge one can use, as long as it’s not dropped.

Tester

1 Like

Thanks, Tester. But, how do you KNOW it’s accurate?

Send it in and get it cal/certed is the only way.

Or, compare it to a gauge that’s been cal/certed.

Tester

Lets see , how simple would it be to go to a tire store and have them set all four tires to the correct pressure. Then use the new tire gauge and see what it says . Most tire stores around here don’t even charge for that . I do give the person who does it it a dollar so he can buy a soft drink . May need to be 2 dollars next time as prices are going up .

And are those pressure gauges cal/certed?

NO!

Tester

I like my cheap digital gauge, it agrees with my bourdon tube gauge and it’s more convenient.

Some years back, Consumer Reports tested tire pressure gauges. I don’t know how many years ago the article was published. If my memory is correct, many of the pencil type gauges weren’t very accurate.

I have a pencil gauge I keep in the glove compartment.
I’ve used it over the years a few times to check tires of family, friends etc. when out and about.
It’s not accurate, but repeatable, so I labeled it with how much it’s off.
It’s there “just in case”, better than nothing, don’t care if it gets rough handling.

I had a high pressure pencil gauge for my bicycle tires that may have been inaccurate. I had a first floor office and there was a bike rack outside our windows. I had ridden my bicycle to work that day as I was doing in the summer. At any rate, we thought we heard a gun shot. A colleague called the campus police and they found nothing. When I got ready to ride my bike home, I found the rear tire had blown out. Apparently, I had overinflated the tire because the gauge read low and the hot weather caused the pressure to increase.

“Tester” has shown a picture of an analog gauge. On it is written its calibration standard:
ANSI 40.1 Grade B. The following is that standard:

“Answer: All Accu-Gage dial tire gauges are ANSI Commercial Grade B gauges (meet ANSI B40 . 1 Grade B specifications), which means that the mechanical accuracy rating is ± 2% from 30% to 60% of scale and ± 3% below 30% and above 60%.”

Of course, this calibration applies to a new unit, so treat your gauge nicely. Thus, a cross-calibration with such a unit would be useful, but won’t be any more accurate than the Accu-gauge. Ideally the Accu-gauge should be purchased with a careful choice of scales so that, your cross-calibration is in its mid-range.
I can’t imagine anything worse than trusting either a pencil gauge or a TPMS. The pencil gauge is even touchy for getting repeated readings, let alone when the slider gets a little dirty.
Finally, consider the range of temperatures and pressures that the tire experiences on a long hot drive or a short cold day. 2% is probably not needed. However, I do think this is an important question, because if you set your tire pressure 5% low and then don’t check it for another year, or only if your TPMS goes off, you might be in trouble. (Mine goes off at 22 PSI…that is, according to my gauge.

Just because it’s a digital readout does NOT mean it’s accurate. The standard pencil gauge can be made extremely accurate. It’s not rocket science. In fact it’s pretty simple. Some are built better then others, but the cheap ones can be just as accurate.

Honestly as long as it’s in the ballpark, you’re OK. Unless you’re doing top-speed runs at the salt flats in a rocket car, you really don’t need overly precise pressures in the tires. Within a pound or two is fine.

You can read all about this:

ASME B40.100-2013: Pressure Gauges and Gauge Attachments

Unfortunately, this cost $155 on Amazon.