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Discussion Starter · #1 ·
My front tire is taking a bit more pressure from the pump to get to higher PSI. I suspect the presta has some stans gunk around it. Will this problem result in artificially low PSI readings on my digital gauge? Pumping the tire to 25PSI feels more like 35PSI. I don't know if its in my head or not. I'm replacing the presta but was curious.
 

· Evolutionsverlierer
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Doubt it, once it clears the valve with higher pressure it goes back to normal at least for me.
Not sure why but lately I have more problems with that so I will start to clean the valve and stem more often.
 

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Discussion Starter · #3 ·
Doubt it, once it clears the valve with higher pressure it goes back to normal at least for me.
Not sure why but lately I have more problems with that so I will start to clean the valve and stem more often.
Yes but if less pressure is released with presta open when using digital gauge wouldn't that result in a lower pressure reading on the digital gauge?
 

· furker
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I have a standard pressure gauge on my floor pump. When I pump up a partially gummed up valve, the gauge spikes up to 100 PSI with every pump stroke and then drops back down over a number of seconds until the gauge reads the correct PSI. As long as some air can get through the valve, it will eventually show an accurate reading.

When it gets completely clogged, the gauge will read zero PSI when I connect the head even when I can feel I have around 25PSI in the tire. When I pump, the PSI will just keep going up as I try to pump and stay high without increasing the PSI in the tire.

I don't think digital would be any different.

I have permanently damaged a standard pressure gauge from over-pressuring the pump. That caused the pump to always read 30 PSI higher than the actual pressure. I'm not sure what a damaged digital gauge would do.
 

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Discussion Starter · #5 ·
I have a standard pressure gauge on my floor pump. When I pump up a partially gummed up valve, the gauge spikes up to 100 PSI with every pump stroke and then drops back down over a number of seconds until the gauge reads the correct PSI. As long as some air can get through the valve, it will eventually show an accurate reading.

When it gets completely clogged, the gauge will read zero PSI when I connect the head even when I can feel I have around 25PSI in the tire. When I pump, the PSI will just keep going up as I try to pump and stay high without increasing the PSI in the tire.

I don't think digital would be any different.

I have permanently damaged a standard pressure gauge from over-pressuring the pump. That caused the pump to always read 30 PSI higher than the actual pressure. I'm not sure what a damaged digital gauge would do.
Oh makes sense. Thanks! I had to rethink how digital gauges work! Eventually pressures would be normalized no matter how much less air is let out!
 

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Idk. I have several different gauges. The one on my pump reads the same as my digital on tubes. But my digital consistently reads a lot lower than the pump only on tubeless, but they read the same on tubes. I too assumed it has something to do with sealant.
 

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I suspect the presta has some stans gunk around it. Will this problem result in artificially low PSI readings on my digital gauge? Pumping the tire to 25PSI feels more like 35PSI.
A restriction in the presta valve will not result in aberrant readings. However, restricted presta valves suck. New presta guts are cheap. You can buy a bag of 10 online, and then just replace them as needed. I probably replace mine every year or two.

BUT... there's more to the story...
When you tap your presta valve to release some pressure, you'll often notice a few misty droplets of sealant on your finger. Sometimes it spews a bit sloppy mess, but there's always a few droplets that come out. These little droplets get into your gauge, eventually accumulating and adversely affecting the reading. You pump up your tire to a high pressure, but the clogged up bourdon tube only moves a little bit. The problem is even more pronounced on electronic gauges.

You can buy the mega pack of gauges and replace them regularly, but that's not very cost effective. For me, I know how my gauges read and how tires should feel by the "squeeze test." My rear tire gets set to 17 psi on my old gauge, and the front to 14 psi. It doesn't really matter what the "real psi" is, as long as you can be consistent in setting them up.

Some gauges measure in an arbitrary unit called psi.
Some gauges measure in an arbitrary unit called kg/cm^2
Some gauges measure in an arbitrary unit called in.Hg
My gauges measure in an arbitrary unit called RustyIrons.

It's good practice to avoid checking tire pressure with the valve at the bottom, where the sealant accumulates. I store my bike with the wheels in a position where sealant won't trickle down into the stems. Then I check the pressures before rolling the bike around. If that's not possible, I use the air hose to blast a little air through the valve, clearing it out, before attaching the gauge. Nevertheless, gauges don't remain accurate forever.
 
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