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valve and pressure question



 
 
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Old April 8th 05, 03:24 PM
Mark Shaw
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Default valve and pressure question

I'm a newbie. I haven't seriously ridden bicycles since I was
in high school, which was thirty years ago. Recently I bought a
nice used Cannondale, and am still getting back into it. So
bear with me, if you will.

I bought a floor pump (Blackburn Airtower 4) fitted with two
terminals, one for Shrader valves and the other for Prestas. I
have Prestas. The pump also has a pressure gauge.

My tires are rated for 80psi. If I pump them to that pressure
by the pump's gauge, and then check with a handheld digital gauge
and a Shrader/Presta adapter, they show about 56psi. If I then
leave the adapter on the valve stem and attach the pump via the
Shrader side of the hose, I also see 56psi. So I pump it up to
80, and check again with the handheld gauge. Dead on.

So I'm seeing two different pressure readings, depending on the
presence of the adapter and which terminus of the pump I'm using.

The tires feel like the readings with the adapter are probably
right, based on my thirty-year-old experience. So I'm probably
going to just continue using it, unless somene raises a red
flag.

I'm curious about what might be going on here, though. Could
the adapter possibly make that much difference?

Thanks.

--
Mark Shaw moc TOD liamg TA wahsnm
================================================== ======================
"All of my mistakes are giving me ideas." - Natalie Lileks
 




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