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I have been commuting on a hybrid for years. A nice CUBE with hybrid tyres with Scrader valve. The odd puncture here and there. Par for the course.

Now I have finally upgraded to a Willier Izoard, with race tyres and Presta valves.

First couple of trial rides, no problem. Then this weekend I went to go out and realised that the tyres were fairly flat. I hadn't ridden this bike for around a month so I figured the pressure had just dropped.

So I topped up with air. Back wheel was fine, took to 110PSI (Max 120). Did the same on the front wheel and went out riding. Within 10 mins, I noticed front tyre was completely flat. It seems the valve failed as I could pump the tyre back up, but then as soon as it released the air just shot out of the valve!

I had a spare tube with me but no pump or tyre spanners. Luckily, I bumped into a very nice Bulgarian chap who was preparing all his kit for a two month cycling holiday and had all his gear literally out in the street. This guy really knew his stuff and within minutes he had changed the inner for me (and way quicker than I could have done it by the way). Had the tyre pumped up (to 100 PSI this time as that's all his gauge went to) and off I went.

Within another 10 mins the tyre was completely flat again. Once more it appeared as if the issue was with the Presta valve, and this time it would take no air in either.

I find it hard to believe that I would get two complete valve failures in the space of ten minutes on two separate tubes, especially when it was replaced by an expert!!

Does anyone have any ideas what maybe going wrong here? I am a bit of a noobie to race tyres so I would appreciate any suggestions? It is a brand new bike, so I doubt it could be the rims, and I checked tyres for holes pinches etc, but it does seem to be the valve. Weird!

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    Did you tighten the small nut at the tip of the valve?
    – ojs
    Jul 11, 2016 at 10:14
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    Consider checking all the options. Sink the old inflated tube in a basin of water. Its not impossible you have a puncture from something embedded in your tyre. If the second tube has a puncture in the same relative place, then that reinforces the puncture. If your valve is leaking, the water test will show that too.
    – Criggie ♦
    Jul 11, 2016 at 11:20
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    I did tighten the nut at the top yes :) I am not that much of a noob :)
    – Ben Warner
    Jul 11, 2016 at 12:56
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    A mistake often made with Presta valves is to over-tighten the nut on top. It only needs to be tightened until "snug" -- over-tightening mashes the rubber gasket inside and makes the seal less effective.
    – Daniel R Hicks
    Jul 11, 2016 at 13:18
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    Are you tightening the plastic cap on the valve without first tightening the metal nut on the valve stem?
    – Kaz
    Aug 11, 2016 at 16:22

1 Answer 1

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Presta valves are fairly fragile things. It's easy to bend the stem once it's unscrewed. They work by the tube pressure being higher than the atmospheric pressure. This causes the valve to be forced closed. It is not until you either loosen (unscrew) the valve and depress the stem or place a pump on it and increase the pressure above the valve until it is overwhelmed and allows air in.

Point is, you can leave the valve "untightened" and air won't escape. The valve mechanism failed because for some reason it did not return to a closed position completely and leaked out. Then when you tried to top off the tire again it was further stuck Two best guesses:

1) You had a run of bad tubes. Welcome to road cycling. Things are more fragile. This is my first choice. Buy a different brand and see what happens.

2) Schrader valves are more durable and forgiving of rougher treatment. Perhaps you were use to them and when you topped off the presta tubes you bent the valve core and it wouldn't fully return to sealed.

Don't give up. I've had bad tubes before.

And one last thing: If you are a valve bender (like myself) I found the cure. Silca and SKS both make a chuck that doesn't need to make contact with the valve core. It uses the pressure from the pump to overcome the resistance of the valve core. Here is the SKS version, currently on sale at Saint John Cycles. You just push it on and pump. Couldn't be easier or more effective. Good only for presta though.

SKS Air Pump Chuck

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  • I did notice the top of the Presta on the first one did seem bent. Maybe that was part of the reason. Thanks I will check. I also intend to test the tubes (If I can to see if there are punctures (with a view to some of the comments on valves above) But the fact I couldnt pump air back in suggest to me it was a valve. But I could be wrong. As I said I am a noob to this
    – Ben Warner
    Jul 11, 2016 at 11:07
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    I usually only unscrew presta valves about half way when filling them. I've found that they are more likely to bend when they are unscrewed the entire way.
    – Kibbee
    Jul 11, 2016 at 15:42

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