How can you possibly trust your tire gauge?

I'm wondering if Xanax might help some? Just one side of your car in the shade and one in direct sun will change pressure a few pounds. Early morning or middle of the day, ditto.

If you really want to worry about a few percent, you also need to only check your tires in a controlled environment at a precise ambient temp and an exact temp of the tire. Should probably have temp sensors in the tires, too.

Then you can first stress about how accurate your temperature gauges are for ambient temp and tire temperature before ever worrying about how accurate your pressure gauge is. It's an obsessive compulsive's worst nightmare or wet dream, depending.
 
redbone3 said:
First of all, Bourdon tube gauges are subject to accuracy problems with change of temperature. Grade "B" pressure gauges generally do not have any temperature compensation. Having calibrated thousands of grade "B" pressure gauges I would estimate that new ones meet their accuracy specifications slightly more than half the time (Ashcroft gauges were especially bad and hard to adjust). Grade "B" pressure gauges are pretty low quality devices and do not hold their accuracy very well. If you can find one, a grade "1A" pressure gauge is good for 1% of full scale over the entire range of the gauge. They are of better quality than the grade "B" gauges. Generally, bourdon tube gauges that are better than grade "1A" are expensive and a bit large for checking tires. I have calibrated numerous digital gauges and have found them to be much more reliable and more likely to pass calibration.

Here is a .5% digital gauge on Amazon. Even if it is out of tolerance and good for only 1% it would be accurate enough for tires.
Click to expand...

I couldn't resist buying one of these when it went on sale for about half price.

Overall, it's a well-presented package, nicely-made, uses common AAA cells (lifetime TBD), and easier to read in a dim garage than the gauge I've been using (an old Accutire Pro, still sold as BMW 82-12-1-467-187 sans the zero calibration button).

I have a couple of those, which are consistent with each other, and a Michelin/Vigil analog gauge. The minor PSI scale on a VDO analog gauge isn't as precise, and makes it harder to compare, but is close as well. Some might consider the latter two "vintage" so they are mostly kept in a drawer, and not used as daily drivers.

The Etenwolf reads ~1 lb max lower than that group of gauges, so if its calibration cert is genuine [9.7 (10), 59.9 (60), 109.8 (110)], then I've been only slightly underinflating for a long time.

I also tested it against some truly vintage 60s/70s pencil gauges (one a Dunlop), and those were even farther off, more inconsistent from reading to reading, and not as pleasant to use in general.

As a practical matter, regular pressure checks already put one ahead of the game that most don't even play, so a pound or so off is more than acceptable, and for very accessible cost as well.
 
redbone3 said:
If you were checking a tire at 30 PSIG the possible error would be +/- 4.8 PSIG. That is 3% of full scale of 160 PSIG. This is assuming the gauge is within tolerance.
Click to expand...
that hasn't been my experience, the gauge has always matched the tpms sensor in the vehicle.
 
b_b said:
that hasn't been my experience, the gauge has always matched the tpms sensor in the vehicle.
Click to expand...
It is possible that your gauge is dead nuts. But, if it were off by 4.8 PSI at 30 PSI it would be within the manufacturer's tolerance. The lesson is if you are buying a bourdon tube gauge choose one that does not measure much above the pressures you will be measuring. Why? The tolerance is a percentage of full scale, ergo the smaller the full scale the smaller the possible error.
 
redbone3 said:
It is possible that your gauge is dead nuts. But, if it were off by 4.8 PSI at 30 PSI it would be within the manufacturer's tolerance. The lesson is if you are buying a bourdon tube gauge choose one that does not measure much above the pressures you will be measuring. Why? The tolerance is a percentage of full scale, ergo the smaller the full scale the smaller the possible error.
Click to expand...
yeah, I wanted one that would work on heavy duty vehicles and trailers.
 
D60 said:
I'm wondering if Xanax might help some? Just one side of your car in the shade and one in direct sun will change pressure a few pounds. Early morning or middle of the day, ditto.

If you really want to worry about a few percent, you also need to only check your tires in a controlled environment at a precise ambient temp and an exact temp of the tire. Should probably have temp sensors in the tires, too.

Then you can first stress about how accurate your temperature gauges are for ambient temp and tire temperature before ever worrying about how accurate your pressure gauge is. It's an obsessive compulsive's worst nightmare or wet dream, depending.
Click to expand...

This is actually a very funny and very good post D60…

We can make t shirts that say instead of Got milk ?

Got Xanax ? :LOL:

I use a liquid filled dial gauge that is seemingly very accurate.

You make a great point about temperature impact on tire pressures… That is a great point to be made.
 
You need one with a calibration certificate traceable to NIST. You can get them for about $250. to $300. that is just a pressure gauge with a threaded male connection. That is how to know how accurate the pressure is.
 
How do you know if your tire pressure gauge is still accurate after the calibration process? Somebody can drop it on the floor during shipping and there goes all that accuracy you paid for!
 
For those of you that compare gauge readings with the TPMS system, keep in mind that the TPMS sensors are just that... not true gauges. By that I mean that they do not have any compensation for the atmospheric pressure outside the vehicle. So as you go up in altitude the TPMS will continue to report the same pressure inside the tire, while a gauge will read higher pressure at the valve stem.
Unless the vehicle's on board systems compensate by using a baro sensor (I am not aware of any that do), then you need to be aware of this phenomenon if you regularly drive at altitude significantly higher than sea level.
 
D60 said:
I'm wondering if Xanax might help some? Just one side of your car in the shade and one in direct sun will change pressure a few pounds. Early morning or middle of the day, ditto.

If you really want to worry about a few percent, you also need to only check your tires in a controlled environment at a precise ambient temp and an exact temp of the tire. Should probably have temp sensors in the tires, too.

Then you can first stress about how accurate your temperature gauges are for ambient temp and tire temperature before ever worrying about how accurate your pressure gauge is. It's an obsessive compulsive's worst nightmare or wet dream, depending.
Click to expand...
Jeez, and I thought I had it bad.
 
My cheapo gauges seem to be close to ehat Ive seen on the tpms. Good enough for me. Whether they are off by a few psi, as long as my tire pressures are consistent, then im good.
 
I find pencils more robust due to their simple operating principle and mechanism. Bought a fancy 0-50psig dial gauge last year - doggone thing experienced a one time 8" drop and now it's done.

If you are at WM grab three of the same model gauges and check them on a bicycle in store with balloon tires. Toss the one that doesn't agree. Modal selection. Yes you can compare five samples, but someone in a blue vest with flair may get inquisitive.

p.s.: Some have hard rubber gaskets on the head, and you loose 3 pounds trying to get a repeatable reading
 
ARCOgraphite said:
I find pencils more robust due to their simple operating principle and mechanism. Bought a fancy 0-50psig dial gauge last year - doggone thing experienced a one time 8" drop and now it's done.

If you are at WM grab three of the same model gauges and check them on a bicycle in store with balloon tires. Toss the one that doesn't agree. Modal selection. Yes you can compare five samples, but someone in a blue vest with flair may get inquisitive.

p.s.: Some have hard rubber gaskets on the head, and you loose 3 pounds trying to get a repeatable reading
Click to expand...
The blue vest zombies at my store DO. NOT. CARE. About anything. They just hire bodies with a pulse, and not enough of them. Good idea BTW.

For that matter in smaller communities the AutoZone and O'Reilly people are pretty chill. I bet if you just told them why you wanted to take 5 gauges to your car in the parking lot they'd let you. Come to think of it, I actually did this once in the Denver area. I wanted to test some Slime gauges before committing.
 
I have been using my Longacre racing gauge for 20 years, thousands of times and it has always been right on. If I really want to know I use my $300 Intercomp gauge that I believe has compensation for altitude/temps and reads in 10ths. Every time you connect your gauge you lose at least a 10th psi.
 

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I use the gauges on the inflators digital they I have. A blue point. And a cornwell. The cornwell is a relabel as I saw someone with a Wurth that was the same.

Typically they are about 0-1 psi off from FCA branded vehicles and have been since put into service. The bluepoint has been going for 20+ and the cornwell probably 8.

Snap on has a newer one but it’s extremely pricey. Like a don’t care if it’s lifetime warranty pricey I can buy many many astros over the years and still be ahead. Which brings me to the next one I would try the Astro.

At home I use an m12 inflator that you dial up and it hits your target. Works great on all the stuff around the house
 
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