Originally Posted by
cyccommute
is it leaking through the top of the valve or from a cut at the bottom of the stem? Although this is a Presta valve, the parts are analogous to Schrader valves although the Schrader valve is clad in rubber. The green arrow points to the core. Core leakage is very rare on either Presta or Schrader. It is also something that is easily fixed.
The red arrow points to the stem. Stems being cut during inflation is very common problem and is due to user error the vast majority of the time. You can cut the stem if the rim has a burr but those are rare. More often, the user pulls on the stem while pumping and cuts the rubber around the bottom of the stem on a Schrader valve. If you are using a hand pump that you pump at 90° to the stem, you are much more likely to cut the stem than if you are using a pump with a hose where the movement of pumping is directed into the ground. If your problem is due to cut stems (more likely than a core failure), you want to reassess the way your pump the tire while on the road.
+1
Originally Posted by
Simeon Hope
Thanks for the information, which I will certainly act on when I'm inflating my tyres.
Are you using a frame pump that fits on the valve at a right angle? Those pumps can work really well and never damage the valve or inner tube at the valve base, but - proper technique is necessary. I use the Zephal pumps (the old HP and current HPX). I hold the pump just behind the head with my index finger wrapped around the pump head and my little and ring fingers around the spokes. This means that all my pumping force goes into my hand and the wheel. The rim rocks some but it is plenty strong, The valve just does what the rim does. No stress on it at all.
I rode sewups for 15 years without a floor pump. Every inflation was with those hand pumps. I killed maybe 2 valves being careless. (And none on my good race tires that cost like gold.)