Quote:
Originally Posted by roastpuff
Question - how the heck do you measure pressure with the pump gauge on a Presta valve? I unscrewed the little nut at the end of the valve, attached my pump, and tried to pump it and the pressure gauge shot up to 100 psi immediately. I don't know if that seems right or not, it felt way too easy. 100 psi on a single pump? Granted the bike tires were already pumped up from beforehand but I'm not sure how this works exactly... It's not like my car tires or MTB tires where when I attach the pump it immediately gives me the pressure reading.
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Quote:
Originally Posted by roastpuff
The gauge has no reading until I start pumping, whereas the other style (Schrader) will read when I screw on the hose from my small 12v compressor. This is what is confusing me I guess.
EDIT: I don't know if I'm reading the pressure in my pump hose or the actual pressure in the tube, that's my confusion.
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presta valves rely on air pressure to hold the valve closed, that's the bit of resistance you feel when you 'burp' the valve after unthreading it. By attaching the pump, you haven't actually opened up the valve. When you pump it higher than whatever's in the tube already, then the valve opens and the gauge will read the tire pressure, which is the same pressure in the hose since it will be at an equilibrium. This isn't an accurate figure because of the amount of air needing to fill the pump hose before it gets to the gauge, but the tire pressure after you finish pumping will be pretty accurate assuming you don't lose much air when you remove the pump head from the valve. Schraeder/car valves rely on a mechanical spring, that's why when you attach an air pressure gauge or pump head, it will open the valve and detects the air pressure. Tip for presta tube users to help save tubes, you don't need to unscrew the end all the way to air up, just a few turns is enough. Screwing it all the way out makes it a lot easier to bend or even snap.
On another note, I attempted the PP climb again. Attacked it pretty hard after the left hairpin and sprinted up about half way before hitting the slight right. I was hoping to save up enough energy to do a sprint after hitting PP cafe, but wasn't to be. I didn't attack the last 1/3 as hard as last time as I didn't have the energy left today lol. I felt like I was able to maintain a steady cadence most of the way up though, but would love to be able to do it a gear or two higher as the summer goes on to help cut the time down. I think being able to push 2 extra gears the whole way would make more difference than attacking harder at the beginning and limping across the finish. 3:28 today, 3:15 would be a nice end of summer personal goal.