I am a staunch believer in proper tire pressure and for many years I have been searching for an answer to a question regarding tire pressure gauges. I have had many expensive and inexpensive ones over the years and in my experience no two gauges read the same pressure. I went as far as taking my gauges to my dealership and they concluded different readings. I am confused as to wish of the gauges I should use and just stick with it. Can you recommend one? I thank you in advance for your input.
First of all putting your name and address om an open web site is dumb. I will Bat Signal a moderator just in case you don’t know how to edit.
Second. your expectations for a tire pressure reading are way to high. Heat - cold - driving and just setting all night might give different readings. @cdaquila Poster listed name an address, please edit.
I like these type gauges. They are very accurate and can be calibrated if you feel the need. Never trust the pencil type gauges. Digital types are OK but I don’t trust the accuracy compared to other gauges.
Racers use these gauges and avoid any errors by always using the same gauge every time the pressure is checked. For home use, always check tire pressure when cold. A final word… don’t get upset by +/-1 psi error in the readings because it does not matter.
My opinion is that the analog dial-type gauges are most likely to be accurate. I have several Accu-Gage ones that read identically. Supposedly those are most accurate in the middle of the scale, so most people would want a 60-PSI gauge (although that means it probably can’t be used on a compact spare).
I love this question. I once worked in industrial instrumentation and always wondered how accurate the cheap and expensive gauges I owned were (I have the image from
a story). There is no simple way to check them (like one can with ice and boiling water for a temperature device), and they cannot be calibrated once sold anyway. One clue I had that they were accurate is that they read about the same as one another. Not a big indicator, but relatively good news. Then I started to get test cars that can read out the tire pressure at each wheel on the dash display. I have found that all of the gauges I own, including the ridiculously cheap plastic pen-type ones I have, all are accurate to within about 2 PSI. That assumes that all these test cars I have compared them to are also reading accurately. And I think they are. The one above posted by Mustangman looks great. I’d buy that one.
Sure they can! At least the better dial type can be. They can be compared to a calibrated gauge with air or the proper way to calibrate a pressure gauge is with an oil and weight test fixture that looks like this;
It uses a precision bore and calibrated weights to apply force over the piston area.
Good to know! None of the ones I ever owned looked like they could be opened and adjusted. Maybe I just need to buy better stuff. Thanks for the cool image.
air pressure changes about 1 PSI for every 10ÂşF in temperature change.
Tires warm up with driving, so you have to let them cool to get a consistent reading.
Measurements are always subject to errors. Without precision lab equipment, the best you can get is probably ± 1 PSI, but that is good enough for most all uses.
Most people set the pressure to 2 PSI above the specified value. Better to be high than low, and that gives you some margin in case the temperature falls.
Check it frequently.
I made the mistake of setting my tires (to 32 PSI) about a month ago, during a rare day when the temp was 70Âş. Not thinking that day. But the coldest day since, about 30Âş, means my pressure was about 28 PSI, still within specs.
I have a 50 year old brass Meisner mechanical dial gauge and two Accd-gage digital ones. Theyall agree and are all 1 pound higher than my dash reading. The Meisner no longer holds the pressure reading when taken off the tire so I usuall use the digital ones. I like the newest one because it uses red led numbers vs the black on gray lcd of the older one.
I probably have a dozen of various types, but the one I use the most is a pencil type (similar to the middle one in GorehamsJ’s photo above) . I like it best b/c it is easy to store in my toolbox, easy to find, and its measurements are consistent one test to the next, and it matches the gauge at the local gas station’s diy’er tire fill compressor. I have other pencil-type gauges that are neither accurate or consistent. I think it has to do with the design of the stuff inside that hole, the good ones keep an airtight seal and aren’t overly sensitive to the orientation of the gauge. When I make a measurement I try to hold it on a horizontal orientation. Other than the merits I mentioned above, I’m not aware of any fundamental reason why one design would be any better than another, consistency and accuracy-wise. The ones I have that look like analog meters, they are pretty consistent, but aren’t very accurate. At least they don’t match my gas station, and they don’t match each other. This topic came up on the show, and Ray and Tom recommend a specific brand of the meter type. You used to could buy it on the Car Talk web page. Ok, I found it, link below
There must be an easy way to test an air pressure gauge to see if its accurate or not. I don’t know what that method is though. If I had to make some kind of calibration myself I’d probably use a bicycle pump, and rig it so I could place a known weight (W in pounds) on top of the handle. Then the pressure at the hose should be W/A, where A is the area of the pump’s cylinder in inch^2. I think that’s correct. Calculating air pressures and fluid pressure have always confused me.
What you just described is what the device @Mustangman posted above (a “dead weight tester”) does. I used one back in 1980 to calibrate some gauges.
The big bugger with an air-only setup are the leaks and a seal screws up the accuracy. A fine, tight tolerance fit with heavy oil allows you to use hydraulic fluid with no seal to calibrate the gauge. The technique, if I remember correctly is to spin the weight a little to eliminate any static friction throwing off the readings.
