Accuracy of pumps

[Polar]

Not many talks about how accurate a pumps or gauge is and according to Cycplus their pumps are within +-1 psi which I don't believe is correct since I get 3 psi different readings on a Cycplus AS2 pro pump and Topeak D2 gauge.
Which one is most accurate?

 

[Paulquattro]

Unless you have the gauges tested and calibrated you wont know exactly .

 

[steve_sordy]

I agree with @Paulquattro , but if I had to put money on it, I'd go with the Topeak D2.

However, the important thing is not how accurate the gauge is but how consistent it is. The D2 is very consistent in my 20-years experience. I spend quite a bit of time getting the tyre pressures that work well for me. Once I have them, I record them and use my D2 to check and set before every ride. If I'm going somewhere markedly different or with trail conditions different, then I may alter the tyre pressures by a psi or two. Because I always use the D2, I don't have to worry about its accuracy.

I use the same gauge to measure and set tyre pressures on my car as well. The gauges found at petrol stations and companies that fit your tyres appear to vary enormously, so I always overfill and then correct with the D2.

 

[Polar]

Unless you have the gauges tested and calibrated you wont know exactly .

How can both be tested and calibrated?

 

[irie]

However, the important thing is not how accurate the gauge is but how consistent it is.

Agree. We always use the same pump (Topeak JoeBlow Mountain Floor pump) with the indicated pressures that we know work best for us in the conditions we ride in (UK South Downs) with the tyres we have (Maxxis High Roller 3 DD front, DH rear) on our bikes (blinged 2022 Trek Rail 5's). Indicated front 23psi, rear 25psi but don't know neither do we care what the 'true' pressures might be.

 

[RustyIron]

How can both be tested and calibrated?

It doesn't matter. It's an exercise in futility. The gauges most of us use are imported trash, and there's nothing you can do to change that.

Over the years, I've accumulated a variety of gauges, both analog and digital. Digital gauges can vary with battery charge. Analog gauges are made of parts stamped from junk material. Both are susceptible to accumulated contamination from microscopic droplets of sealant. I've found that most start giving grossly erroneous results after six months or a year.

A while back I decided to "calibrate" my gauges. I found a couple that were in agreement at the pressure that I run my tires. I assumed that those were more likely to be correct. I set the other gauges to show the same reading as the "correct" gauges. On some, the "zero" was off, but that doesn't really matter for what I was doing.

Despite putting in a lot of effort on calibration, consistency didn't improve. Over time, the readings on the gauges changed again. Needless to say, I was disappointed.

My current setup is to set the pressure using the gauge on my Joeblow Mountain pump. The pressures I like are 26/23 on THAT pump. Maybe the actual pressures are different, but it doesn't matter as long as I can fill my tires to the way I like them. This pump is just over two years old, and the pressures still seem consistent. If the gauge starts getting weird, I'll eventually be able to feel it on the trail.