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As the name suggests, my front bike tire's inner tube has suddenly started leaking air for no apparent reason. I used my bike on Sunday on a fairly rough trail, but everything seemed fine afterwards. The following Wednesday, I used my bike to go to work and once again, I didn't notice anything out of the ordinary.
This friday morning however, I decided to check my bike's tire pressure and noticed my front tire was slightly deflated, nothing major. I started to remove the cap from the Presta valve and air started leaking like crazy until it lost all air and the core somehow fell off. I assumed that the issue was simply with the core being loose, screwed it back on and inflated my tire back to full, with my valve leaking absolutely no air this time.
However, after a mere 100m on my bike, I could already notice that it had lost some air. I left it at home and came back to a completely deflated tire.

I'm confused. How come it didn't leak much, if any air from Wednesday to Friday, and now cannot hold air anymore, despite the fact that it was stored in my appartment? Is this a faulty valve? I don't have any specific reason to believe I could have punctured my tube either on Wednesday.

Thanks a lot for your help!

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    Photos of the core would help. Did you inspect the tube/tire for punctures?
    – Paul H
    Nov 4, 2022 at 19:55
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    I can't post a picture right now but it's honestly just your run of the mill Presta valve. It's in pristine condition as the bike and tube are only a few months old. The core doesn't seem to have any visual defect
    – Althos
    Nov 4, 2022 at 21:07
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    There could be several different causes. The fact that it seems to leak worse when you monkey with the valve suggests that either the valve core is loose or there is a cut in the tube near the base of the valve stem. Probably you should remove the tube, inflate it, and stick it in a tub of water to check for leaks.
    – Daniel R Hicks
    Nov 4, 2022 at 21:33
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    Honestly, the most sensible thing to do is to just ditch the tube and install a new one. I used to spend hours chasing down problems with old tubes, but it's just not worth it. The nice thing with tubes is that they're cheap and quick to swap out. I still always feel a bit guilty when throwing away a tube that could potentially still have been used, but then I tell myself that the environmental impact is pretty minute compared to all the food packaging, transport, other new parts that I'm also responsible for.
    – leftaroundabout
    Nov 5, 2022 at 15:12

1 Answer 1

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There are basically two possibilities:

  1. Your valve is damaged. It could be damaged in a way that is causing a slow leak and leaked explosively when you jostled it.

  2. You have a very small puncture in the tube and the explosive leak at the valve just a coincidence.

As Daniel Hicks mentions in a comment, the best thing to do if you really want to know for sure is to inflate it and put it in a bucket of water. I find with a leak that slow, I usually have to inflate it quite a lot to get a good stream of bubbles.

You could also just replace the tube. The main problem with doing so is that there may be something stuck in the tire, or a burr on the valve hole in the rim, that will just puncture a new tube in the same way.

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