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Today I encountered a puncture. I pulled the tube, ran my fingers around the inside and outside of the tire carefully looking for the offending object, found nothing, so concluded it was probably a pinch flat (I had just hit a pothole). I installed a new tube, being careful to seat it properly to avoid pinches, and re-inflated. Within seconds the second tube was flat. That being my only spare tube and my only CO2 cartridge and it being dark and a very long walk home, I called the sag wagon (aka my wife).

Back home, I removed the tire from the rim, turned it inside out, inspected carefully, and found nothing. Ditto with the rim and rim tape. And, I should add, these are virtually new tires and rims with barely a hundred kilometers on them.

When I looked at the second tube that failed, I found this:

enter image description here

Those slices are directly opposite the valve stem, and a careful re-inspection of the tire and wheel at that location revealed nothing. But as you can see, they're quite large slices. I might suspect a faulty tube if it were just one slice, but two? That seems extremely unlikely to be a faulty tube.

I know no one can tell me exactly what happened, so my question is what are the possibilities? What the heck could have made cuts that large that occurred without even riding on the wheel and which couldn't be felt with my fingers on inspection?

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Perhaps someone used a utility knife to open the carton containing the tube. –  Daniel R Hicks Nov 2 '13 at 2:52
    
(What did you find on closer inspection of the first tube?) –  Daniel R Hicks Nov 2 '13 at 2:53
    
I opened the box the tube came in and didn't use a knife, so that's not it. The first tube had similar but even larger slices. It's as if two big chunks of glass that I couldn't feel magically appeared in my tire. –  Carey Gregory Nov 2 '13 at 3:11
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It's definitely a vampire. Being so close to Halloween, this is not uncommon. –  Kibbee Nov 2 '13 at 14:40
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And did you try another tube once you got home? If so, what happened with that one? –  jimirings Nov 2 '13 at 16:12

2 Answers 2

I patched both tubes yesterday, partially inflated them, and let them sit overnight (without being in a tire). One of them was flat today, so I tossed it as probably having an unseen slow leak not worth finding. The other one I remounted and rode 40 miles today without problem. So apparently either: 1) I somehow damaged the second tube mounting it, or 2) there was something in the tire I never saw or felt on inspection and it fell out without me noticing.

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Chapeau Carey, it takes a brave man to go for a 40-mile ride the day after such a long walk home! –  PeteH Nov 2 '13 at 23:49
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Thanks @PeteH, but I ended up getting a ride home from the wife. But she chuckles and won't let me forget it for a while. –  Carey Gregory Nov 3 '13 at 6:01

That looks like a standard pinch flat. If you're not familiar, Sheldon Brow explains:

Pinch Cuts result from hitting stones, curbs, or sharp edges of holes in the road surface. When the tire hits a sharp edge hard enough, it compresses so that it bottoms out. The inner tube can get pinched between the rock and the rim. Pinch cuts usually put two small holes in the tube. This type of damage is sometimes called a "snake bite" because the two holes look like the wound made by the fangs of a snake.

Pinch cuts sometimes ruin tires as well as tubes, but usually the tire will not be damaged.

The impact that causes a pinch cut can also make a dent or "blip" in your rim.

Although, I'll agree that those are rather large cuts for a pinch flat, but the alignment/position strongly suggests that.

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It was my first thought as well, but then the OP writes "that occurred without even riding on the wheel" which should rule out pinch flats. Also the fact that the wholes occur twice at the same wheel position ("directly opposite the valve stem") is rather improbable for pinch flats. –  Benedikt Bauer Nov 4 '13 at 14:59
    
Doesn't look anything like a pinch flat. The holes are too large and are not positioned right for a pinch flat (assuming the OP is telling us correctly where they are located). And pinch flat holes will have fairly obvious abrasions around the actual hole. –  Daniel R Hicks Nov 4 '13 at 15:46
    
@BenediktBauer and Daniel are right -- That's a brand new tube that had never been ridden on, so it can't be a pinch flat. And yes, it was directly opposite the valve stem. –  Carey Gregory Nov 4 '13 at 21:37

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