two different tire pressure guages, two different results Help!

Factual Questions
1

I’ve been maintaining my tire pressure with one guage. I have a little nook in my side door which holds my CDs, pens, fliers that I’ve been meaning to throw out, etc. Little did I know that I have two tire guages, the exact same one (both from the same insurance company). I have no idea which one I’ve been using and have only made the discovery yesterday. One guage is 5 psi off from the other one. Which guage is actually correct? Do I have to resort to buying another guage?

2

Which one is correct? Who knows? They may both be wrong. Invest $15 and buy a good one and then use the good one you have, assuming one is good, as a backup. Either that or live with the fact that you will never know for sure… 5 pounds either way usually isn’t life or death.

3

Ah, metrology. My favorite field. :wink:

This reminds me of an old saying: “A man with one watch knows what time it is. A man with two watches is never sure.”

With just two gages of (more or less) equal accuracy, it is impossible to determine which gage is inaccurate. Heck, for all you know, both might be inaccurate.

Here are some options:

  1. Buy a third gage. With luck, two of the gages will read close. If this happens, these two gages are probably good. (Though there’s no guarantee, as it’s possible both have a similar offset error.)

  2. Calibrate a pressure gage by comparing it to a standard pressure gage. (If there’s an engineering school near you, go ask a grad student if he wouldn’t mind checking your pressure gage against a standard.)

  3. Buy a good, expensive pressure gage that you believe is accurate, and will retain its accuracy over time.

4
      • If you are really concerned about a 5-PSI difference and you have the sliding-type gauges, throw them away and get a dial-type gauge, the dials tend to read more accurate.
        ~
5

They’re pretty cheap too.

6

My dad has a dial-style gauge - I don’t like it, and I think it broke. For ~15$ on sale (whoa, 35$ today) at Canadian Tire I picked up an awesome digital-readout style gauge with a backlight so you can see it at night. I’m sure you can get one for much less that has the same stuff inside just a cheaper plastic case with no light.

I like being sure I’ve got the final pressure, the little rod didn’t get sticky, etc. etc.

7

Throw them both away and get one from Summit Racing or Snap-On.

8

5 psi in the rear tires of my car can be the difference between moderate corner-entry understeer and violent lift-off oversteer on entry.