This is a quick yet VERY scientific cheap tire gauge test.
Methodology:
Aired up a tire testing all against this Motion Pro Professional Tire Gauge
From left to right:



Craftsman Digital 8 Years old
US General 4x4 From HF. 3 years old
Victor From Advance Auto NEW (with custom foam and duct tape surround)
No Name HF Inflator with gauge (The stem lock works well on this one!)


WINNER: the US General 4x4 was ***** on and the cheapest.
Craftsman was 10PSI short on all readings.
No Name inflator was 6PSI Short on all readings.
Victor was 4 PSI short on all readings.


At least they're consistent.



So there you have it. With what I suspect is zero QA at these price points, this little exercise doesn’t mean yours is off. Lots of good units out there from motion pro, joes garage etc. You get what you pay for. Sometimes!

 

WoW,Thanks for taking the time to inform us.I will sleep better tonight,but I wonder how you knew the tire pressure to begin with.

 

All well and good but how do you know the MP gauge is accurate?

 

Indeed! As an engineer I understand the principle of calibration and we need a calibrated gauge to give us a decent comparison.

 

I think this is a good post and appreciate it. But without knowing the verified pressure to begin with none of the data is helpful. I think we all know that air pressure gauges fluctuate wildly from brand to brand. I use the same one all the time so I get repeatable performance.

The next time I have my torque wrenches calibrated I may have them check my air gauge. Then I'll know what to add or subtract to get exact pressure. Barring that, if you have a few of them around you could probably see if there's a trend (low or high) and figure that as your "actual".

 

Reminds me of a few years back when I had an alternator go bad on an old truck. Went to parts store for a new one, guy says "Let's test your old one - yep, it's bad". He puts a new one on the counter for me, I said "Let's test the new one". Tested - BAD. Two more new ones tested - BAD.
The machine was bad, I took one and went on my way. (My old one really was bad)
I doubt if they ever fixed that machine.
Good to start with an accurate point of reference.
I guess that's why I never see radiator cap psi testers any more at the parts stores...

 

The test is invalid without a calibrated gauge.
However you did show that not all gauges read the same!

 

Several years ago I became obsessed with finding an accurate tire pressure gauge.


For my "standard", I built a mercury manometer. Because of size limitations, mine is only capable of going from 0 to 32 psi. Even at that it stands almost 7-feet tall including the valves and frame. It is calibrated at 0.5 psi increments. Note that 0.5 psi results in a vertical change in mercury level of slightly over 1/2". Therefore it is easy to estimate down to ounces of psi. The vertical scale was calculated mathematically and then engraved accurately on a milling machine.


I purchased several of the gauges you mentioned in the op plus a few others I had laying around. Most were close . . . varying within +/- 2 psi. Only one was right on from 5 to 32 psi.


I won't mention brands because the most accurate one I have might have been a fluke. I will say, however, that the most expensive one I purchased was not the most accurate. In fact, the cheapest one [a digital] was one of the most accurate.


The worst were the "pencil" type.

 

Yep, we calibrate depth/pressure gauges all the time in our line of work. We use a Druck calibration gauge ( $$$ ) built to exacting standards for that purpose. It too must be periodically re-calibrated and certified to be of any real use.

I don't mean to pee on the OP's post or the idea behind it. He has pointed out something we riders need be aware of. Gauge error and drift can account for highly misleading information. Being out by 10 psi on a 40 psi measurement is a whopper !! Having more than one of the cheap little gauges we rely on, to use as a X-reference, wouldn't be a bad idea at all. They really don't cost much, all things considered.

 

When I was at engineering college, a long time ago, we tested a few tyre gauges and the pencil type were surprisingly accurate. I use a dial type nowadays, but to buy a calibrated one ain't cheap. Unfortunately 'calibrated' all too often simply means a gauge has graduated markings, not that it has been verified as accurate.