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Tire going flat without riding, but doesn't have a puncture... what gives?

Discussion in 'Bicycle Mechanics' started by eimaiosatanas, Feb 27, 2012.

  1. eimaiosatanas

    eimaiosatanas Speeding Up

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    Hello people,

    Another noob question follows. Recently, I experienced the following phenomenon twice: I parked the bike, and after coming to pick it up 8 - 24 hours later, the front tire had practically gone flat.

    The funny thing is, the tube doesn't have a puncture anywhere. I took the tube out, pumped it, and there was no apparent loss anywhere. ...So... what gives?

    The first time this happened, I checked the back tire, and as soon as I took the protective cap off, the tire just instantly started losing pressure right in front of my eyes, as if I was pressing the valve :eek:! I pumped both tires, rode for 30km, no problem.

    But this has left me puzzled. Does it have to do with the cold? Is the tire valve messed up? FWIW, I'm using swabble 700 x 23 ~ 28 tubes, both front and rear.

    Any help appreciated! :D
  2. trad

    trad Speeding Up

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    Slow leaks can be tricky to find. Suggest dunking portions of the tube in water (while inflated) to see where the leak is.
  3. Edogawakikkoman

    Edogawakikkoman Maximum Pace

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    OOOps...delete... please.
  4. eimaiosatanas

    eimaiosatanas Speeding Up

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    I will try this later in the evening. If something strange is going on I'll report back!
  5. joewein

    joewein Maximum Pace

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    From the description I would suspect a misbehaving valve. It's more consistent with an intermittent problem than a puncture of the rubber tube itself.

    So you're having a problem at the rear too, not just the front? That is a weird coincidence. It is interesting that you would see something on both tyres at the same time. One might expect a simultaneous pinch flat from going over the same hard object on both tyres, but not two valve problems.

    I take it you properly screw the Presta valve down before you put on the protective cap?

    Maybe there is some dirt in the valve mechanism(s). It might even be dirt from inside the pump (rust from condensation or rain?), such that both valves got contaminated from the same pump. Is the pump new? Do you use more than one pump?
    I second trad's suggestion. We always used a bucket or a bathtub for that purpose.
  6. eimaiosatanas

    eimaiosatanas Speeding Up

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    I'm mostly using a topeak pocket rocket II to pump up the tires. On a rare occasion, I do use other pumps (e.g. at the bicycle parking lot, or a bike shop) over which I have no control.

    Here's the thing though about the tubes. I installed them 3~4 weeks ago, and they're the exact same product. Thus, I think the possibility of the valves misbehaving is not so far fetched.

    When I took the protective cap of the rear tire off, the tire instantly lost pressure, as if I was pressing the valve down. Frankly, I was quite surprised (presta valve was properly screwed at the time!).

    Another thing that I could theorize is that the pump that I'm using is stressing the valves and may have damaged them (it's a keitai pump after all, and when pumping the tire the valves are being stressed by unnecessary sideways forces).

    Finally, although I haven't submerged the tubes to know for sure that they're still good, I have ridden ~50km, on and off of pavements and bumps and stuff, and air pressure was maintained (quite well I might add).

    All in all, my guess is a combination of stressed valves and metal contraction due to cold lead to some abrupt loss of pressure... will investigate further and report back!
  7. StuInTokyo

    StuInTokyo Maximum Pace

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    I had a mysterious flat tire on my trailer without a hole, found out an asshat neighbour was letting the air out of my tire :eek:
  8. bird

    bird Speeding Up

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    This is what came to my mind reading your initial post, and even more so if you regularly use a mini pump.
    Just my two yen, if you haven't checked this yet...
  9. kiwisimon

    kiwisimon Maximum Pace

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    Dog turd in a mailbox? I hope so. Latex gloves are a great thing now you can buy them at the home centers. And I don't even have a dog, least likely suspect ever.
    But is revenge when it's anonymous really revenge?
  10. eimaiosatanas

    eimaiosatanas Speeding Up

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    I DID manage to bust a previous tube like this! However, that one didn't have a ring to bind to the rim, so it was wildly going up/down/sideways during pumping.. The new tubes do have a ring to keep them in place and I keep it reasonably tight. Will definitely check this again.
  11. zenbiker

    zenbiker Maximum Pace

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    It sounds like you are unscrewing the valve when you unscrew the dust cap.
    Make sure the valve is screwed in fully. And throw away the dust caps. They don't serve any useful purpose and and very unpro!!:cool:
  12. bird

    bird Speeding Up

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  13. eimaiosatanas

    eimaiosatanas Speeding Up

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    Front tube is good.

    So, I took out the front tube, submerged it into water... and the tube is good. I was checking the damn thing for five minutes, no air bubbles, anywhere, whatsoever.

    I guess it has a bad case of the "funky-valve".

    Actually, this.. sounds quite plausible regarding the rear tube. :eek: Oh well...

    Either way, I tightened both valves as firmly as possible with bare hands, we'll see how it goes...
  14. DeltaForce

    DeltaForce Speeding Up

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    There's no way you can get the valves securely in the valve stem with bare hands. There should be flats either side that you can use a spanner on. Doesn't need to be so tight, but you need a spanner on it.

    As for the knurled part we screw closed after pumping, that wouldn't matter even if we didn't close it. Air pressure keeps that closed. So of course, with bare fingers is the only way.
  15. eimaiosatanas

    eimaiosatanas Speeding Up

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    Thanks, duly noted! :D

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