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I recently had a flat and replaced the inner tube. It pumps up just fine, but then when I leave it and come back it's completely flat. I replaced the tube twice more, with the same result each time.

The the punctures were

  1. Just to the right of the valve on the rim-side, not a clean cut but a small hole as if the material had been stretched or twisted too far.
  2. Roughly opposite the valve, a 6 or 7 inch gash, not straight. I couldn't tell whether this was rim-side or tyre-side.
  3. Just to the left of the valve, rim-side, a clean hole about 5mm long.
  4. edit: replaced rim tape, put in new inner tube. 2 minutes later I hear it go pssshhh, same result as number 3.
  5. edit: added second new rimtape on top of first, new tube, 2 minutes, pssshhh, same result as number 4.

I'm using the process described in this video, except that I don't use a tyre lever to put the tyre back on after inserting the new tube (because I've previously made the mistake of pinching the inner tube and making a hole), instead I just use my thumbs to push the bead over the rim.

I've examined the inside of the tyre and the rim, I haven't found any aberrations (no spokes sticking through rim tape, no holes or foreign objects anywhere). Edit: chap in repair shop had a look at the tyre and confirmed it seems fine.

Could these different failures all be caused by the same thing?

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    I'd guess #2 is a red herring (bad tube). Are you checking that the valve is free before inflating (push the valve in after seating the tire; it should move freely inward) and the rim+tape is in good condition near the valve? – Batman Sep 18 '16 at 13:16
  • Yes the valve moves freely. The rim tape is not in perfect condition (slightly worn) but doesn't seem rough enough to cause a puncture. I am going to try replacing it anyway. – Brendan Sep 18 '16 at 13:36
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    Replace the rim tape it works wonders. And examine the inside of the tyre. – Carel Sep 18 '16 at 14:27
  • Possibilities: 1) You're damaging the tube when you install it. 2) You're running tire pressure way too low. 3) The rim tape does not fully cover the holes in the rim. – Daniel R Hicks Sep 19 '16 at 1:33
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    One important point: When installing a new, out of the box tube, inflate the tube first, just to the point where it holds its shape. Installing a flat tube and then inflating it will as often as not lead to folds in the tube which result in tears while riding. – Daniel R Hicks Sep 19 '16 at 1:35
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So, I think the problem is that I have a 25mm tyre on a rim designed for narrower tyres. That means the rubber surrounding the valve is distorted into the narrow valley of the rim, which puts stress on it. As @Batman suggested, failure #2 seems to be a red herring.

So, I've opted for the narrowest tube available and furthermore used a cutting from an old tube to provide padding around the valve, like this, so that the rubber doesn't have to distort so much to reach the base of the rim valley.

It's still inflated so far, will mark this solved if it's still inflated at the end of the day!

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Often this is a result of the innertube getting pinched between the rim and the tyre when you change it. It can also simply be a result of poor tyres. Since I switched to Schwalbe Marathon Plus' on my road bike I've not had a single flat. Great, hard-wearing tyres.

A few things to try: Check the inside of the rim for rough edges on the metal that could be peircing it from inside. Get a Coolstop Tyre Lever - not only does it help you prevent pinching it makes getting even the most difficult tyre onto the rim. Clean out the inside of your tyre when you change the inner-tube. You'd be surprised how much crap works its way in there.

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