mrblue

I have two pumps:

• Silca Pista Plus
• Topeak Joe Blow Sport

According to my Topeak digital pressure gauge both pumps are off by ~3 to 5psi. Could it be possible the pumps' gauges are right on and the digital pressure gauge is off?

Thanks.

aggiegrads

Yes, it is very possible that the digital gauge is the one that is off.

a digital gauge is always precise, but not always accurate. Just because there is a third significant does not mean that it is right. The Silca is accurate to 2%, so I would trust that as your standard so long as it hasn't been dropped.

In practice, it really isn't all that important as long as it is consistent. If you know that the topeak is 5psi high, then you can compensate when you inflate.

alcjphil

Are you taking tire pressure after you have used the pump?. In order to take tire pressure using a gauge, you have to release air from the tire which will give a lower pressure. In high volume low pressure tires this is not an issue. In low volume high pressure tires this can make a noticeable difference which could easily account for the discrepancy you have seen

Bill Kapaun

Any digital display is +/- 1 digit plus the inherent inaccuracy of the display.
Any display can't be more accurate than the data inputed.

mrblue

I am inflating a 25c tire to 80psi, according to the built-in gauge on the pump. I remove the chuck without bleeding or anything. Then, I check the pressure with the digital gauge and the pressure reads ~5psi less than the built-in pump gauge. And the discrepancy between the pump and the digital gauge is the same for both pumps. So this leads me to think perhaps the digital gauge is off.

Bill Kapaun

Check the pressure twice and see how much you lose in between.

Troul 

Check using the digital gauge 1st....

70sSanO

Does it matter?

I mean, how many years have you been riding happily at the incorrect pressure?

You can always inflate 3-5psi less and see if you like that better.

John

MudPie

This is definitely something to consider and a likely explanation for the decreased pressure for subsequent measurements.

The best way is to put a gauge in-line during the pumping process, and you can view two gauges in the exact same condition. Practically speaking, you'd have to splice a gauge into the hose.

Remember, a person with two watches is never confident of the correct time.

mrblue

No, it doesn't really matter. I was curious about which of the three gauges was most accurate.

However, I am beginning to think they are all accurate. I noticed that when I release the chuck a quick spurt of air comes out. I believe this is the ~3-5psi discrepancy between the pumps' gauges and the digital gauge.

Iride01 

Unless you have them tested to determine what it more correct, then who can say which is the more accurate? Sure, we can look at other articles that suggest one or the other is more accurate, but you'll never know if you are the one that goes against the majority.

Use the one you trust. If your ride pressure is determined by a formula or suggestion of others, then I don't know what to tell you. I use the pressure that feels right for me when I ride my bike. Too high a pressure and I feel every crack, bump and grain of sand. Too low a pressure and my legs feel like I'm climbing a 20% grade when it's only a 6% grade. Yes I'm exaggerating for those that are Sheldon Brown Cooper wanna-be's and have problems determining sarcasm and such. <grin>. But over the many years of riding, I know what psi feels right to me, and only me.

70sSanO

It makes life easier to just assume the digital gauge is correct. I’ve checked a couple of floor pumps with a digital gauge just as a reference point.

Now if you really want to open a can of worms, get another digital gauge... lol.

John

philbob57

If 2 gauges agree, why not believe them? Why believe the one that is the outlier?