I recently fitted new tires and inner tubes (Continental 700 25c). Today I had a fairly slow puncture, going flat in around 20 mins. I removed the tube and found that the puncture was at the edge of what appears to be a defect in the surface of the tube, at the point where the top seam meets the edge of this apparent defect.

Is this most likely caused by the tube being pinched or folded somehow when installed? I'm guessing that I've done something wrong here, rather than there being any issue with the tube itself.

  • Try laying out the tube beside the tyre. The tube should be the same size around as the tyre. If its significantly longer while flaccid then the tube's too long to use and folds like this happen.
    – Criggie
    Commented Mar 21, 2017 at 20:13
  • You can have defective tubes but they would typically go out immediately.
    – paparazzo
    Commented Mar 21, 2017 at 20:39
  • Instructions bicycles.stackexchange.com/questions/1235/… I also take em up to 15 psi then drain to let folds relieve. It was in the instruction for a tube I bought.
    – paparazzo
    Commented Mar 21, 2017 at 21:17
  • @Criggie I believe the length is correct. Having replaced and re-inflated, I reduced the pressure and took a look between the rim and bead and found that the tube had in a few places been pinched under the bead. I'm not sure whether that kind of pinch could cause the problem I had here.
    – chrisw
    Commented Mar 21, 2017 at 21:34
  • 2
    It looks to me like the tube was possibly crimped/twisted when inserted into the tire. You should always inflate a new tube enough to "puff it out" a bit before installing. This prevents both getting the tube twisted and getting it caught under the bead. Commented Mar 21, 2017 at 22:09

1 Answer 1


Would you have scratched the tube, it wouldn't have taken 20minutes to go flat (95% of the time you simply cannot inflate a tube that is scratched during installation).

This is mostly some sort of storing issue, you usually got that when hanging your inner tubes on a hook. It's a rather common thing to observe in second-hand tubes that don't go directly from the box to the wheel, the rubber get compressed and once inflated you get this weird look.

Or you can, but it's rarer nowadays, have this in a brand new tube, just being caused by non homogeneous rubber distribution, it happened to me sometime ago.

Most of the time and from my experience if the deformation is not to pronounced (and it does not seem that way here) it should not cause any problem since the inflation will simply fit the shape of the tube into the tire.

It's uncommon but with bad luck the deformation could cause a hernia to happen but then again with a hernia your tire would have not taken 20 minutes to go flat (usually goes boom and flats out in 2 seconds).

I would go with deffective tube rather than wrong installation here.

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