owc6

I get more of a variance if one side is getting sun and the other is in shade.

KenHorse

Exactly

If the gauge is spec'd to "5% of Full Scale", it's still going to be no worse than 5% at 30 PSI, right?

So 1.5 +/- @ 30 PSI it is

Patman

The problem with those OnStar readings is how do you know when they got that data? Was it when you were driving and the tires were warmed up? Was it in the middle of the night on a colder evening? Tire pressure varies by about 1psi for every 10F change in ambient temperature, and it'll also vary by about 3 or more psi from when you first start out and when the tires are warmed up after driving a while. So your tire could be 30psi first thing in the morning when it's 50F out and 35psi in the afternoon at 70F while on a highway drive.

FunDriver

Sounds about right. Seems there would also be a noticeable variance if one tire is flat and the other isn't.

owc6

That would be my '05.

Frodo

My TPMS readings always match my gages. I think it's pretty accurate technology. I say gages because I don't know if a single gage is accurate. They don't calibrate most gages because its expensive, just like they don't align your front end at the factory. By having several gages on hand I can check a questionable or new gage against the others. Any that don't agree with the group readings gets tossed. Could I be in error by having the group out of range? Yeah, but its better than having only one gage and not knowing anything.

blueray16

My TPMS has consistently run 2 psi lower than my 15 year old longacre analogue 2.5" gauge.

Just got a new longacre magnum 3.5" analogue (52-52001)this week and it is reading same as the TPMS
The larger dial makes reading and adjustments down to 1/4# a lot easier. Winner!

jimtreber

Some time back I took more than a handful of various analog and digital self calibrating hand held tire gauges to try and every one varied in readings. I worked at Honeywell at the time so I had their aircraft gauge calibration department build me and calibrate a large analog tire gauge and that's all I use. I just now compared it to the DIC and it is within 1 pound.

Gearhead Jim

orca1946

How accurate depends on what ypu are doing. Daily -- fine. Track - a Costly gauge is the best.

Bill Dearborn

What is a good quality hand held gauge? If you do a check of all the available gauges including the cheap pencil sticks you will find they read quite closely to each other if the resolution of the gauge permits. Even if you pay for the most expensive gauge if it isn't calibrated on a regular basis (every 6 months or so) it isn't any better than the pencil stick gauge. Usually the more expensive gauges don't have all that much better accuracy but they do have much better resolution, I spent $75 for my Long Acre large dial gauge because I can read the gauge easily and it makes it easy to bleed tires.

Bill

JMII

I didn't spend that much but I too went with a larger dial (2.5") Joe's Racing model because you can easily read ever # of pressure. Since most vehicle tires are happy somewhere around 30 PSI the 60 PSI gauge is recommended as I've been told the accuracy is highest at the mid point. I've found all those cheap digital gauges are nearly worthless because the batteries always die when you need them the most. Then they take some odd size watch battery you can never find.

Patman

I have a digital gauge that I got from Radio Shack about 15 years ago and I think I've changed the batteries only once so far and they use a pretty common watch battery that can be found in just about every dollar store. Since the batteries last so long it's not that big of a deal when they do die, it's not like I'd be without a gauge for days and days. I'm not sure what you mean by "the batteries always die when you need them the most" though. When would you need the handheld gauge the most? If your tire is flat, or getting low, the TPMS will tell you that info.

I love using the digital gauge to set my pressures because it reads in 0.5 psi increments.

madrob2020

33 posts & counting on the merits of various air gauges. This Forum is always good for a few laughs & thankfully some GOOD info occasionally!

JMII

My truck is older and doesn't have TPMS and my boat trailer has nothing, so I must check those manually... and often (monthly). So maybe that's why I kill the batteries. I also track my car which means lots of checking so my use case is not the norm. Regardless its frustrating when you go to use something but find you can't because the battery is dead.

Patman

The forum does tend to get a little crazier this time of year when people are bored because their Vettes are put away for the winter.

CptCvMan

Not the way it works unless your gauge only goes to 30 PSI, and then it is 1.5 PSI +/- at all pressure reading.
If your 30 PSI gauge reads 30 PSI, then it would be 28.5 to 31.5 PSI.

If you have a 50 PSI gauge, then you are 2.5 PSI +/- at any pressure.
If your 50 PSI gauge reads 30 PSI, then it could be 27.5 to 32.5 PSI.

You likely have a gauge rated higher than 30 PSI as you would not want to stress the internals every time you check a tire pressure.
This is on analog. Have not had much dealing with digital as we found them easy to knock out of calibration so we stayed away from them.

KenHorse

Uhhhhh no.

A percentage is a percentage regardless of the value it is extrapolated from

If a gauge is spec'd at +/- 5%,

5% of 50 = 2.5
5% of 30 = 1.5

It doesn't matter what the measured pressure is. 5% is 5%

You're simply wrong

BrunoTheMellow

I have not counted but it updates like every 15 seconds or so.

CptCvMan

Last time I will try. You are not understanding the concept of full range accuracy.
The +/- is not based on the pressure you are reading off the gauge.
It is based off full range. Lets try using a different number to see if it helps.
You have a 100 PSI gauge. Full range would be 100 PSI. With me so far?
5% of 100 PSI is 5 PSI. The gauge can be off 5 PSI at any given pressure.
It is not 5% of any given pressure, but the FULL RANGE.
In this example, because the full range accuracy +/- is 5 PSI, a reading of 50 can be 45 to 55 PSI or, wait for it...........
10% off. As you go further away from full scale, it increases the error as a percentage of pressure.