How can you possibly trust your tire gauge?

[Sequoiasoon]

The low pressure light came on in my car this morning so I grabbed the tire gauge in the glovebox and checked one. Imagine my surprise when it rocketed up to almost 50 psi. The tire was no more than 35 psi even before the light came on, so that gauge is worthless. That’s the worst example, but every tire gauge I have reads different. I finally decided to standardize on a US made one I bought from Amazon, but I still have no idea if it’s accurate.

How does someone find out what the true pressure reading is on a tire, or to calibrate a gauge?

Best pressure gauges

I have this JACO Elite one after other replies to another pressure gauge thread. I like it as it goes to 100psi for the higher trailer tires and spares. I might get more for the other cars. It's on sale currently and I like that it does to the .1psi not just .5 for the Slimes.

My other 5 cars I maintain have pencil gauges that are pretty close as spares. They all have a Slime one like this that is used regularly and close to the JACO when checked. At least pretty consistent that I know of. There is a newer version that supposedly seals better to valve stem.

I can set the tires on the cars on a cold day, no sun, after sitting for 12 hours overnight and some of my TPMS sensors on the Pilot, Tucson, Renegade read different then the JACO and the other vehicles by 1-2 psi.

The Slimes have gotten me through YEARS of flat even tread wear. If I see or measure odd between center and edge of tires, I'll adjust my cold inflation pressure accordingly. The JACO has batteries that can be replaced easily and I think will serve the same dedicated accurate enough for my daily drives well for a long time.

 

[gman2304]

Joes racing dial gauge. It’s within a lb of my Milton gauge and the TPMS on my wife’s car.

 

[SubLGT]

Buy a gauge that includes a credible calibration certificate.

Calibration Specialty Vehicle Tire Gauge Assembly - Calibration Specialty, Inc.

Our Vehicle Tire Gauge is customized by you, and assembled and calibrated by us; NIST Calibration certificate included! Choose from the provided 1% accuracy analog or 0.25% accuracy digital gauges, and chucks; hose length is dependent of chosen chuck. View our Certificate of Accreditation here.

calibrationspecialty.com

Or send your existing gauge to an accredited calibration lab.

 

[CapriRacer]

That's a good question. It might be worthwhile to find out what gauges racing teams and tire testing organizations use. Maybe @CapriRacer can jump in here.

Is it more important for a gauge to be precise or consistent (within a certain margin of error)?

Well, it isn't so much which gauge, as it is the calibration. Our testing groups had a certified test port traceable back to a government weights and measures organization. There was a strict schedule and procedure for calibrating both the usage gauges and the test ports. Each location had at least one conveniently located. There was even one at the corporate headquarters - and there was nothing but offices in that building!

OK, and the difference between precision and accuracy (consistency): A precise gauge has lots of significant digits - like 32.43 psi.

An accurate gauge gives you the same number all the time (within the margin of error). Usually those 2 things went hand-in-hand, but it would be better to be accurate but imprecise, rather than precise, but inaccurate!

Each gauge sold should have an accuracy statement.

So what's a layperson to do? Get several, and the odd man out is likely suspect!

 

[SHOZ]

I use one that has a regular screw in pressure gauge but they are not very durable if thrown around. You can get as good a gauge as you want.

 

[willbur]

The low pressure light came on in my car this morning so I grabbed the tire gauge in the glovebox and checked one. Imagine my surprise when it rocketed up to almost 50 psi. The tire was no more than 35 psi even before the light came on, so that gauge is worthless. That’s the worst example, but every tire gauge I have reads different. I finally decided to standardize on a US made one I bought from Amazon, but I still have no idea if it’s accurate.

How does someone find out what the true pressure reading is on a tire, or to calibrate a gauge?

I've got about 8. They all are preety close to each other except for one that is old and dropped on the cement over the years

 

[willbur]

Well, it isn't so much which gauge, as it is the calibration. Our testing groups had a certified test port traceable back to a government weights and measures organization. There was a strict schedule and procedure for calibrating both the usage gauges and the test ports. Each location had at least one conveniently located. There was even one at the corporate headquarters - and there was nothing but offices in that building!

OK, and the difference between precision and accuracy (consistency): A precise gauge has lots of significant digits - like 32.43 psi.

An accurate gauge gives you the same number all the time (within the margin of error). Usually those 2 things went hand-in-hand, but it would be better to be accurate but imprecise, rather than precise, but inaccurate!

Each gauge sold should have an accuracy statement.

So what's a layperson to do? Get several, and the odd man out is likely suspect!

deleted

 

[SHOZ]

If you are in the lab you are dropping the last digit, it's insignificant.

I use a digital Slime one along with the analog one.. The analog one car read line pressure or tire pressure. Good for comparison. The Slime one is what it is until it goes dead.

 

[SubLGT]

......An accurate gauge gives you the same number all the time (within the margin of error)......

I think you are referring to precision, not accuracy.

The Difference between Accuracy and Precision Measurements | Precisa

This article aims to clear up the confusion, exploring the difference between precision and accuracy and the correct way to use each term.

www.precisa.com

What is Accuracy?​

Accuracy is defined as ‘the degree to which the result of a measurement conforms to the correct value or a standard’ and essentially refers to how close a measurement is to its agreed value.

What is Precision?​

Precision is defined as ‘the quality of being exact’ and refers to how close two or more measurements are to each other, regardless of whether those measurements are accurate or not. It is possible for precision measurements to not be accurate.

What is the difference between Accuracy and Precision?​

Both accuracy and precision reflect how close a measurement is to an actual value, but they are not the same. Accuracy reflects how close a measurement is to a known or accepted value, while precision reflects how reproducible measurements are, even if they are far from the accepted value. Measurements that are both precise and accurate are repeatable and very close to true values.

 

[wavinwayne]

At home whenever my tires get a few psi low, I use my Park Tools bicycle tire pump to inflate them. It has a gauge on it that has proven accurate to +/-2psi. As a side benefit, I get a good arm workout.

 

[nwjones18]

The TPMS on the Maverick is within one psi of the $8 Milton pencil gauge that I've had for 10+ years. It is even accurate compared to BMW's Motorrad TPMS system. Very good system BTW. Also the Milton is within 1 psi of my 32 yo BMW motorrad pencil tire gauge, which is from when my 1991 R100gs was new.

Here is the one I have S-921. Has only gone up $2

Amazon.com

I bought a Milton after having some other cheaper pencil gauges and its still around 4 psi off from what my trucks TPMS says.. Maybe I need to try another.

 

[Lenny5160]

That's a good question. It might be worthwhile to find out what gauges racing teams and tire testing organizations use. Maybe @CapriRacer can jump in here.

Is it more important for a gauge to be precise or consistent (within a certain margin of error)?

In drag racing, you find what works best on your car, with your gauge, and you only use your same gauge. Someone else's gauge will likely vary by 1/2 psi or more. That kind of variance is no problem on a daily passenger car but a big deal when tuning for high horsepower with about 5 psi in the tire.

But the top teams are most likely using a $400 Buxton or Intercomp digital gauge.

 

[97prizm]

Is your gauge mechanical or digital? I've had consistent readings with Accutire brand gauges and the results are identical to one another (comparisons with the same model). I don't think consumer grade versions are designed for calibration by the user since this is not practical.

My digital accutire with an led light is really accurate. I had discount tire fill my tires to 36 psi then compared my digital gauge.

 

[CapriRacer]

I think you are referring to precision, not accuracy.

The Difference between Accuracy and Precision Measurements | Precisa

This article aims to clear up the confusion, exploring the difference between precision and accuracy and the correct way to use each term.

www.precisa.com

yup, you're right. I got that backwards. I wonder what I was thinking.

 

[redbone3]

Hey guys! Ever hear of calibration labs? Not a cheap solution but if you are that concerned about a gauge accuracy it is the only real solution. Google calibration laboratory for your locale.

 

[barryh]

There is no reason for a pencil gauge to suddenly become wildly inaccurate unless there is substantial stiction in the mechanism. The operating principle is a piston and extension spring. The very simplicity should allow for good accuracy if they are well made and initially calibrated.

Having calibrated hundreds of industrial bourdon tube gauges I disagree that they are fundamentally more accurate than a pencil gauge especially when we are talking of small 2" or 3" gauges with low quality mechanisms. The operating principle of a bourdon tube is inherently non linear and the mechanism has to convert this into a linear rotation on the dial which is challenging to do accurately in small cheap gauges. By comparison the pencil gauge uses a single extension spring which is inherently linear within it's designed range and there is no conversion of that movement taking place.

What ever the type of gauge, they can be re-calibrated, including pencil gauges, just unscrew the head and you will see how they work and how to change the anchor point of the spring. The OP has hit on the real issue which is what do you use for a reference source. A calibration shop would have reference gauges checked against a dead weight tester which is a fundamental device. There is nothing similar available for DIY use at low cost. The best you can do is to own several gauges and keep track of how they compare with each other.

 

[SubLGT]

There is no reason for a pencil gauge to suddenly become wildly inaccurate unless there is substantial stiction in the mechanism. The operating principle is a piston and extension spring. The very simplicity should allow for good accuracy if they are well made and initially calibrated......

Milton says they have disadvantages:

.....All of our Milton dial tire gauges are ANSI Commercial Grade B gauges (meets ANSI B40.1 Grade B specifications). Unlike piston-plunger-type gauges, the bourdon tube movement is not affected by changes in temperature, humidity, altitude or air stream contaminants. The mechanical accuracy rating is ± 2% from 30% to 60% of scale and ± 3% below 30% and above 60%....

Feature Friday: ACCU-GAGE® by Milton

Why Do You Need a Tire Pressure Gauge? When you maintain the right air pressure in your tires, you can maximize the life of your tires through all types of terrain and weather conditions, whether your ride is an RV, motorcycle, bike, car, truck, or trailer. Choosing the right tire pressure...

miltonindustries.com

 

[SubLGT]

Milton is claiming +/- 0.05% accuracy with their new digital gauge/inflator, now on sale for $180 (usually $229). But they don't include a calibration certificate.

Precision Digital Tire Inflator & Pressure Gauge (0-160 PSI), Extreme ± 0.05% Accuracy s-580e

Precision Digital Tire Inflator & Pressure Gauge (0-160 PSI), Extreme ± 0.05% Accuracy Milton Industries Presents the first of its kind…. Precision Digital Inflator Gauge The Precision series offers a variety of features which makes it the ultimate tool

miltonindustries.com

Milton® Presents the first of its kind. Precision Digital Inflator Gauge

The Precision series offers a variety of features which makes it the ultimate tool for professional technicians, diehard prosumers, and the performance racing market.

Unparalleled Accuracy
Gauge features up to 20 times greater accuracy than the most exacting products currently on the market. Using precisely engineered components, it has four units of measure: PSI, kPa, BAR and kg/cm2 with a range of 0-160 PSI plus an unheard accuracy of +/- 0.05%.

 

[redbone3]

Milton says they have disadvantages:

Feature Friday: ACCU-GAGE® by Milton

Why Do You Need a Tire Pressure Gauge? When you maintain the right air pressure in your tires, you can maximize the life of your tires through all types of terrain and weather conditions, whether your ride is an RV, motorcycle, bike, car, truck, or trailer. Choosing the right tire pressure...

miltonindustries.com

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.

Amazon.com

 

[carviewsonic]

I have three of these Slime one like this. They all check within 1 - 1.5 psi with each other and with a dial gauge similar to this one



I've stuck with these for years and occasionally replace a Slime gauge with another one when the batteries die. I'm getting decent life (mileage) from the tires.