Tire gauge again

Yesterday I had my tires rotated and requested the tech to inflate to 34psi.

This morning I checked them with a one of my dial gauges and all tires read 28psi, rechecked with another dial gauge and it read 34psi.(all readings were taken cold, in my garage. My three pencil gauges all provided different readings. The dial gauges are good gauges. How do I tell which is correct. I’m leaving for a 1500 mile trip Sat and would like to tires inflated to 34psi.

Thanks for any input

Well, I’d like to think the shop has an accurate pressure gauge (and that they actually listened to you), so I’d call the gauge that says 34 the accurate one.

Pencil gages are only useful for helping keep your pocket protector in your pocket.

How cold was your garage?
Were both dial gages stored in the same temperatire?

Metrologists (calibration guys) will tell you (correctly) that nothing can get calibrated accurately until the calibration equipment and the gage have stabilized to the same temperature. If one of the gages was stored in your cool garage with your car and the other was stored in your nice warm cellar, I’d be inclined to believe the one from your garage…and attribute the 28psi to the tires being cooler than they were in the tire shop.

I have two good gauges. I compare results to verify that they are both the same and likely correct. I have a pencil gauge that works OK, but I just can’t bring myself to really trust it.

I thought that decent quality bourdon tube dial gauges were supposed to be unaffected by temperature. Maybe not?

Anyway, I recently had a collection of gauges similar to the OPs with similar reliability issues. I went out and bought a quality bourdon tube dial gauge, used it to test all of my existing pencil gauges and such, threw most of them away and kept the 2 good ones. I keep the dial gauge out of harms way as my “calibration” device and use the others on a normal basis.

If you had 2 dial gauges that far apart one of them must have an issue - stop back at that shop and ask them to check each against theirs - toss the one that is off from that (obviously).

I use the dial pressure gauge. I tried both the cheap ones (the pencil type) and found the round one (barrel) was just as untrustworthy as the square pencil type as they both stuck.

Consensus is the magic word for you. Buy enough tire pressure gauges and you will find that the group will gravitate toward the correct number.

I have dial gauges (judged by some as the gold standard) that read in error as well as pencil gauges (judged by some as rubbish) that read accurately. It’s a good thing to warm a pencil gauge in your hand in cold weather to improve its accuracy if it is known as being accurate in warm weather.

Store and handle your good working gauge carefully to help to keep it good. As was said, keep what you believe is a good gauge in reserve as a reference.

All of what I said is only a fervent hope so the best that you can do is to have your gauge checked by a scientific instrument calibration service at least at the pressures where you will use it. It will cost you between 30 and 50 dollars.

Most shops like to go high on the pressure, so I bet they are up to 34 PSI. If you can still feel all the bumps in the road, you should consider letting some air out, depending on the recommended pressure on the sticker on the door or door frame.

Thanks for all the input. Some good points were brought up. One dial gauge was stored in the cooler garage the other was in the car. I checke the tires again this morning and there’s still a discrepency with both of them stored in the garage overnight. The difference is still 6 lbs. I am going to use the more expensive and newer gauge, set the tire pressures at 28lbs (recommended psi). The higher gauge will give me a reading or 34psi, so I’m still in the ballpark as far as the drivers manual goes. Thanks to all for the information and advice.