How to calibrate/check tyre pressures and pumps?

[alanmclean]

Hi
I bought a Topeak tyre gauge which reads considerably under my two track pump gauges which in turn disagree with each other by about 10psi.

How can I find out which is correct? I cannot kid myself that I can estimate tyre pressure with my thumb: I can only work out too soft/ok/too hard this way.

Is there a household/workshop workaround standard to calibrate pumps or at least something which gives a reliable and repeatable benchmark?

I don't want single figure accuracy but it would be good know when I am within 10 psi or so.


Regards

Alan

[commendatore]

I use a single pump as my baseline. I believe the gauge reads low, but it's what I've based cx tire pressure off of for years.

The actual number is irrelevant at this point. I know what 25 psi from that pump feels like, and I can go from there.

[Rick]

I work in a place with very aggressive instrument calibration programs, so I wondered about this myself.
You could send it to a certified laboratory for calibration, but that is way too expensive and inconvenient for a home mechanic.
So once I went out and bought bout a dozen really cheap pressure gages from different sources $1 to $6 and then just made numerous pressure reading comparisons. I also have two "good quality" gages on tire pumps and another stand alone gage that was pretty expensive and was calibrated when new, but that was ~20 years ago.
I was pleasantly surprised that all the gages read exactly the same on typical pressures to within the accuracy of my ability to read the gage.
So if I had an "outlyer" I would just have trashed it. You could just compare with some other gages, even at a gas station, or with friends, and if they all read the same, they are "probably good" because it is unlikely that two inaccurate gages would all be exactly the same inaccuracy.

[sungod]

op - how are you comparing gauges?

best is to connect them to each other (using a long valve extender for instance) then pump and see what they read

fwiw i've got a two track pumps and an sks digital meter, all three measure the same using the above method

[alanmclean]

thanks for replies, I just pump up a tyre to say 100psi on one pump and then stick the gauge and the other pump on in turn. There is a little pressure loss for sure but I have consistently different readings. A consistent error would be ok but I just need a benchmark thing to set up.

[alanmclean]

thanks for replies, I just pump up a tyre to say 100psi on one pump and then stick the gauge and the other pump on in turn. There is a little pressure loss for sure but I have consistently different readings. A consistent error would be ok but I would like a reliable benchmark/baseline which does not involve lab certification. Using this for CX and playing with tubeless road tyres which can run lower pressures but I really don't know what my pressures are. Maybe I should just use one track pump:-)