Road Cycling - Are floor pump Guages accurate?

I just got a new Joe Blow Sport pump, works great... I think. It sure beats the heck out of hand pumps, but I'm wondering if the guages for them are accurate. I checked it with a little zefal hand pressure guage I have and it appeared to be only good to +/- 10psi. Is this normal? It looked to be fairly inaccurate. Just making sure :rolleyes:

I just got a new Joe Blow Sport pump, works great... I think. It sure beats the heck out of hand pumps, but I'm wondering if the guages for them are accurate. I checked it with a little zefal hand pressure guage I have and it appeared to be only good to +/- 10psi. Is this normal? It looked to be fairly inaccurate. Just making sure :rolleyes:

Well, they'll have a certain built in inaccuracy of course. But also remember that you can lose a bit of pressure just removing and attaching the chuck. It wouldn't be 10 psi (probably around 3 to 5) but think about the sequence of events:

pump tyres to pressure P
remove chuck and lose ~5psi
attach hand pressure guage and lose another ~3psi
factour in combined inaccurracies of both guages (~+/-2psi ea.) and if they're both in the same direction, you can easily see how you're ending up with close-to or more than a 10psi differential.

Gee, I disagree with Deadbeef. When I remove the pump from the tire there is a rush of air. That is the air that was between the bottom pump valve and the tire valve. You should not loose any air from the tire unless your pump lacks the lower valve or in removing the pump you jar the tire valve stem. I always pump my tires up a little higher than is recommended on the tire, namely to 130 psi. I like the crisp low friction ride. By quickly applying your hand gauge and releasing it you should be able to loose a negligible amount of air. You can easily test that by repeating the process. I do know that when I absent-mindedly over inflate my tires, repeatedly testing the pressure with a gauge alone is too slow a process. I don’t know what the gauge actually reads on my floor pump at the setting arrow but from experience I know that it is 130 psi when I reach the mark just from years of experience. Trust your hand gauge and if it happens to be a little off don’t worry about it, your tire pressure is not that critical. Years ago the Bicycling Magazine tried to find out how the manufactures determined the tire pressures they specified on their side walls. Only one manufacture responded, and it turns out they were just guessing. Your riding comfort is the important thing. One stretch of pavement that I frequently ride on is getting so rough that I am glad to let the tires get a little soft between inflations.

ANY gauge can be inaccurate... Without calibrated testing, determining which gauge is more accurate than another is a total crapshoot.

A (motorcycle) racer friend of mine (and regional class champion, too) said that he swore by digital gauges. "Throw 'em against a wall, and as long as they still turn on, they'll still be accurate," he said.

I had an older, analog Meiser Accugauge (with no hose) and a newer gauge of the same brand, but with a short hose on it at the time. About $20 apiece. The owner of my race team had a digital gauge the same brand as my other friend, also $20. I had another friend with a fancy, liquid-filled, oversized gauge that cost about $75.

At the Dunlop truck, they have a test rig with a calibrated gauge that anyone can use to check their gauges. I took all of the above gauges and checked them every morning of every race weekend for 4 months (this equaled to 12 days of testing).

The Verdict (in order introduced above):
#1) Consistent within 1/2 psi every time.
#2) Varied within 3 to 4 psi up or down.
#3) Varied within 5 psi up or down (the digital one!?!).
#4) Varied within 5 psi up or down.

The tires we run are run at 32psi front and 30 psi rear. This equates to 1 psi being about a 3% difference. To further this, being 5 psi off equals being over 15% wrong! On a racing motorcycle, this can be a downright dangerous situation.

The same degree of inaccuracy in a 120 psi road tire works out to being 4% or less. Also, this inaccuracy is less likely to create the injury-threatening situation that you experience on a 160+ mph machine.

The Moral: Unless it's a critical application, just use a gauge that you have a good feeling about.

The Lesson: Always use the same gauge to reproduce consistant pressures to the inflation that you like the ride of. Take good care of that gauge and don't abuse it. If it has a mechanical "Reading Hold" feature (the little bleed valve/pressure hold button on the side), ALWAYS relieve the pressure after use. Leaving it pressurized will cause the bourdon tube inside the gauge to take a "set" and cause your accuaracy to drift.

ANY gauge can be inaccurate... Without calibrated testing, determining which gauge is more accurate than another is a total crapshoot.

Reminds me of the time I went to Home Depot to buy one of those large dial thermometers for the back yard -- there were about a dozen or so on display and no two read the same temp, with about a 10-degree spread from lowest to highest!