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I'm on my second inner-tube in as many weeks and the culprit seems to be the same between them; these diagonal marks on the side around the whole of it—but only on one side (sorry, didn't make a note of what side that was when removing it :(). Some are shallower, some deeper; the second picture below is the one that was actually leaking.

When I took it in to my LBS the guy said I pinched the tube with the tire bead when installing it, but I have a hard time imagining that I somehow managed to pinch the entire tube all along one side, in such a regular pattern (the marks repeat regularly, every 1"), twice in a row.

I wouldn't call myself a bike expert, but I have, from time-to-time, replaced tubes; did my front wheel and it's been fine for months. Did I just get lazy/cavalier in my tube installs or is there some other explanation?

Diagonal marks in side of inner-tube Close-up of marks on an inner-tube; this one was actually leaking

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Those are scuff marks from running the tire flat (or nearly so), or from a tire whose sidewall is breaking down. –  Daniel R Hicks Sep 1 '13 at 19:58
    
Definitely from an under-inflated tire. –  alex Sep 2 '13 at 3:45
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@DanielRHicks on further inspection it was the latter (why didn't you post it as an answer :P), the inner-most fibers broke and were sticking in, constantly irritating the tube till it punctured. I don't know how I damaged the tire; I've never rode on it flat, though it was fairly old. –  Nick T Sep 2 '13 at 4:41
    
One suspects that underinflation played a significant role in the tire failure. If you can see "ripples" in the side of the tire while you ride it, it's way under-inflated. What size tire is this and what pressure do you usually run? (And how often do you check it?) –  Daniel R Hicks Sep 2 '13 at 11:46
    
@DanielRHicks 26x1.95, I'm more commuting vs. trail riding nowadays so I inflate it to 50-60 psi. Don't have a gauge, but if I notice additional give in it I re-inflate (usually around 20-30 psi). May not have noticed it one time though. The damage seemed peculiar though; only one wall had fibers frayed (other was basically pristine), and in the same regular, ~1" apart, pattern (between which, also clear). –  Nick T Sep 2 '13 at 20:08
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3 Answers

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Those are scuff marks from running the tire flat (or nearly so), and/or from a tire whose sidewall is breaking down.

One suspects that underinflation played a significant role in this tire failure. If you can see "ripples" in the side of the tire while you ride it, it's way under-inflated. One wall of the tire will tend to fail before the other, based on the rotation and the diagonal cord alignment. The spacing corresponds to where the tire rippled as you rode it -- it repeats in the same location on each rotation since the sidewall gets softer and softer there.

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That does look like scuff marks from installing it, but I agree you wouldn't find them all the way around. It may be the tube was twisted and when you inflated it, it untwisted and scraped itself against the bead. Try dusting your inner tubes with talcum powder before installing them. The talc will lubricate the tube and allow it to move freely against the tire and rim without scuffing.

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Do you have a picture of the inside of the wheel you are running them on and the tires you run? I think you'll find the same pattern there.

This is probably what is called a pinch flat.

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I don't think so. A pinch flat usually produces just two small holes, not a whole series of them. And they definitely wouldn't be found around the entire tube. –  Carey Gregory Sep 1 '13 at 22:11
    
It could if you continually rode on an under inflated tire. –  Christopher Scott Sep 3 '13 at 14:37
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