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My tires have a recommended inflation pressure of at least 33psi and a suggestion maximum of 40 psi. I have a bicycle pump which can read 0-160psi and took a reading and it read 28psi so I added air until it reached 33. I took a reading with a gauge that pops the stick or but it read 42psi. I then tried the gauge on a battery powered pump at it read 38psi.

Two of these reading are out of spec so if either is right the pressure if wrong. The third is a bit high but I trust it the least because the reading didn't seem to change enough as I let air out. I need to go for a long drive early tomorrow before any service stations are open so I can't just go there for a second opinion. Which gauge type is more likely to be accurate?

  • I don’ trust the small ones on pumps - they tend to be really cheap... I have a digital one and it matches the garage one which is 4 inches in diameter. – Solar Mike Sep 29 '18 at 5:52
  • I wouldn't trust the bike bump, they aren't even close to accurate. It's just a toy because they know that you'll know when a bike tire is full. I'd personally trust the 42 psi, even though the 38 psi is only 3 psi off, it is still a cheap add on to catch the consumers eye, while those stick pressure gauges are made specifically for one purpose, and have been around for generations because they're accurate – user38183 Sep 29 '18 at 5:55
  • @user38183 Well I wouldn't call it a toy, it's actually a pretty decent model that was recommended for cyclists, not kids on bicycles. Hard to recommend a tire gauge that's going to read 10 pounds under when you're inflating 120psi tires for a race... although I hear what you're saying and my first impression was the stick tire should be better, but I have had two stick gauges in the past that disagreed by 5psi on the same tire, so I guess that was kinda lingering in my mind. – Michael Sep 29 '18 at 5:59
  • @user38183 Also the thing that concerns me about the bike gauge is that it may actually be calibrated better for higher pressures – Michael Sep 29 '18 at 6:00
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    @user38183 On a bike tire: 32-22-20, added air, 35-25-30 (stick, powered, bike)... bike pump seems to get less accurate as the pressure gets lower, but at the higher pressure it's still within 5psi of the stick, unlike on the car. I'll probably just go with the stick but try to get outside confirmation as soon as possible. – Michael Sep 29 '18 at 6:49
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A precision mechanical gauge with correct range for your application is one you can trust. For your application, I recommend a 0 - 60 PSI mechanical gauge. If the scale goes up to higher values than 60 PSI, it usually means the precision and accuracy are worse.

With precision mechanical gauges, the accuracy is typically 1% of the maximum reading, so in your case, it would be 0.6 PSI. For 0 - 140 PSI, it would be 1.4 PSI. So here you can directly see the benefits of using the correct range.

Electronic ones can be pretty good too, but then you'll have to renew the batteries occasionally and you can never know if low battery voltage results in sightly incorrect readings.

Although this is not a product recommendation site, I'll provide one link for manufacturers of precision mechanical tire pressure gauges: https://www.flaig-praezision.de/en/products/tyreinflatorgauge

Note that if you have a donut spare, it typically has higher pressure and you cannot use 0 - 60 PSI gauge for the donut spare because the pressure is over 60 PSI.

Don't trust the gauges of cheap Chinese pumps! I once pumped my car tires to what I believed to be 2.3 bar. Turned out the real pressure was much, much higher, because the cheap Chinese pump had a low quality gauge. Typically, a cheap Chinese pump costs a fraction of a good precision mechanical gauge. Then when you consider that only a fraction of the pump cost goes to the poor gauge on the pump, you realize that the poor gauge costs a fraction of a fraction of a good gauge.

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