Howdy,
I notice my trucks tire pressure display does not match my manual tire pressure gauge. The tire pressure is close but it’s not exactly the same.

Meaning, I’m not sure which tire pressure is correct.

Please let me know your thoughts.

Adios.

 

that’s been my experience; i rely on eyesight and manual tire pressure readings

 

My manual gauge and truck display are right on the money.
Doesn't mean their correct, could be off the same amount.

FYI, You can watch the pressure change as the tires warm up.

 

The TPMS sensors are there to tell you when a tire is becoming dangerously low. They are far from precision devices. Purchase a decent quality tire pressure gauge and rely on that. Even then, things can be off. I have both a mechanical and a digital tire pressure gauge. Neither was particularly cheap. Most of the time they agree to within 1/2 lb. But not always. They almost never agree with the TPMS readings. Usually differing by 2 or 3 lbs.

 

The comments previously mentioned are all right on.

Since it's not a critical application (a couple psi won't matter that much), just use your gauge.
The gauge is easier to use when inflating the tires, so that makes it the practical choice.

I tend to keep mine between 37 and 40 psi, so being off a little doesn't matter one way or the other.

.

 

A man with a watch knows what time it is, a man with two watches is never sure. . . . .

 

A stopped watch is precisely correct twice a day. A watch that gains (or loses) 1 second a day is correct about once every 236 years. Which is more useful?

 

The tire pressure displayed on my 2019 F-150 matches my calibrated pressure gauge within less than 1 psi. I know, "one in a row is not a trend", so other trucks might not be as accurate. I have the advantage of working in a calibration lab where I can check my pressure gauges. Some good name brand gauges are not very accurate and some cheap gauges are accurate. You never really know until they are checked.

 

This was what I was thinking just because you check it manually doesn't mean it's right but I believe you need a good gauge

 

Absolutely.

The problem with getting a good gauge is that they are pricey and not as easy for the average person to find. By that, I mean that most people don't know what is a good brand or grade of accuracy to look for in a gauge.
Plus, as mbw919 mentioned, unless you get it with a certified calibration chart or compare it to a known standard (NIST traceable) ....you won't know how accurate it really is.
Having a gauge certified will add somewhere between $30 and $100 to the cost of the gauge. If you live near a city, there should be at least one business nearby that offers calibration services, if you want to have your gauge certified.

Overall, for tires, I don't think it's that big of a deal. In my experience, nobody makes a 'good' tire gauge and good gauges are not used or sold as tire gauges (except in racing, such as dragsters, Indy, Nascar, etc).
When new, most (but certainly not all) decent gauges are within spec. Unfortunately, the way tire gauges are used is pretty hard on them. Doing things like dropping them on the ground or banging them around in your toolbox can hurt accuracy.
Also, the act of popping them on and off the tire stem quickly causes issues because of the pulsation and shock to the movement....it's best to apply and remove pressure in a way that causes the needle to travel smoothly, and not be bounced up or down.
I have a snubber on mine, which restricts airflow to eliminate this issue.

In the price point for tire gauges...I suspect the mid to upper range digital gauges are probably more accurate than the $0.50 mechanical ones from China that you pay $10-15 for at the parts counter.
The parts counter gauges will usually be grade D, which is +/-5% of the range. So, if you had a 100 psi gauge, the reading could be up to 5 psi higher or 5 psi lower than the actual tire pressure.
Some of the better tire gauges that I've seen use an ASME B40.1 grade B gauge, which is 3-2-3%....and that would allow an accuracy of + or - 2% in the middle half of the range (from 26 to 75 on a 100 psi gauge).

I did stop at Discount Tire the other day to have air added to my truck tires. They had a machine where they input the pressure you want on a digital screen and then the machine inflates up to 2 tires at a time to that preset pressure (the air chuck clips onto valve stem, so the guy doesn't even have to stand there holding it).
Since it uses transducers, I expect it is at least accurate to 1%, probably even 0.5% since that's a typical accuracy grade for industrial devices.

I wrote all that to suggest not getting too lost in the search for an accurate gauge. If you have one that is pretty accurate, try to handle it nicely and it'll maintain its accuracy much longer.
If you are a type-A person and reeeeeeally want to know if your gauge is accurate...you can take it to a calibration lab.

 

I have three old-style stick gauges and a couple of electronic ones. They are all pretty close to each other; probably +/- 1 PSI. Most of the time I use one of the electronic ones, mostly because it is the easiest to read. It happens to be within 1 PSI of the dash display, so I'm good. I realize this may not be the case with everyone, but once you know the relative difference, I think it's easy to compensate.

The only question is which is more accurate. I gauge mine by the pressure set by the tire store when I get my tires rotated/balanced. Since it's their business to set this, I figure they have some skin in the game.

 

I bought a JACO Deluxe Tire Pressure Gauge - 100 PSI, from Amazon, and like the way it operates.

How accurate is it? I can't be absolutely sure, but it matches within 1 psi or so the readings on my dash and on my aftermarket Bellacorp TPMS system.
Bellacorp TPMS

I bought the Bellacorp system as I can use it on my truck and all my trailers. This is an outstanding product and I strongly recommend it. Bellacorp customer service is second to none. I use it in addition to the factory tpms system on my truck, as it mounts externally on the valve stem.

All 3 seem accurate even as tire temp changes. I run my truck tires at 55 psi, and my trailers all take 50 psi. Gives me a feeling of confidence.

 

As long as you have something you feel is reasonably accurate, I think you are good to go.
A note on the accuracy I posted about.....that is the limit to how 'poorly' it can perform.
So, in the case of a grade D gauge, it should be at least accurate to +/- 5%...it could be within 1% or even dead on...it just needs to be better than the 5%.

I think today's manufacturing processes probably create more accurate gauges, even in the tire gauge market.
Of the different ones I've used, I don't recall ever coming across one that I felt was off by much.

 

I have a $12 digital Accutire MS-4021B - seems to match my mechanical gauge as well as the display in truck. I leave it in my glove box and keep a 12v compressor on board.

I can see getting an expensive, calibrated gauge for mission-critical applications. Would be overkill for me personally.

 

So, just to throw a curve into this discussion, lets say you have a "good" quality tire gauge that reads from zero to one hundred psi and advertises an accuracy of 1% of full scale. That's pretty good. It means that it's accurate to plus or minus 1 psi. So the tire you inflate to 35 psi could be anywhere from 34 to 36 psi.

So far, so good. But the air pressure in your tires will increase or decrease by 1 psi for every 10 degree temperature change. Check your tires in the evening when no sun is shining on any side of your vehicle and the outside temperature is 50 degrees with your "good" gauge and adjust the pressure to 35 psi. Actual pressure could be 34, 35 or 36 psi. Check the pressure mid day when the ambient temperature is 85 degrees and get a reading of 38 / 39 psi. So, in reality, your pressure is anywhere between 34 and 40 psi.
It all depends on the ambient temperature, the accuracy of your gauge and the relative humidity of the air in your tires.

Oh, and for the Nitrogen fans out there, the expansion rate of nitrogen is about the same as air. There are really only 2 small advantages to using nitrogen. First, pure nitrogen contains no water and second, nitrogen passes thru the rubber of your tires slower than air so you will lose less over long periods of time. Of course if you don't have a bottle of nitrogen and the necessary regulators handy in your garage you blow that idea as soon as you top off with compressed air.

So, take a shot at the correct tire pressure mid-day in at least a couple of seasons (winter to summer) and just drive.