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Just had a flat and having problems finding the thing that pierced the tube in the tire. Normally I just run my fingers around in it, until I found it, but this time everything looks O.K.

My experience is though, if you do not find the object, another flat will happen soon ...

I know the trick with searching for the puncture on the tire in the same space where the hole is on the tube. I even flipped the tire so that the pattern is inside, but nothing to be found.

It's a mountain bike tire, and the hole in the tube is very tiny.

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Well, I checked again using some of the tips, nothing to be found. So I put in the repaired tube, and it seems like it is fixed. Maybe it fell out, or it got washed away while I de-iced the tire in the shower before the repair. Thank you for your help! –  Paul Weber Feb 14 '12 at 17:27
    
I had big problems with cable frays (the little slivers of brake cables after you cut them a little shorter). Something that helps me find the offender is that ALWAYS line up the tire label with the valve stem and ALWAYS on the right side of the bike. Then, when I find the hole in the tube, I can just line it up with the tire and will at least know where it was. Some times it will just be a puncture where the object was before it fell out, not uncommon. –  BillyNair Jun 12 '12 at 4:10
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7 Answers

up vote 15 down vote accepted

The object that pierced the tire and tube may have been left behind or it might be embedded in the tire but hidden in the rubber. This can happen with small pieces of glass, wire, or thorns, especially in thicker treaded tires such as those found on a mountain bike. When the rubber of the tire is compressed against the ground the offending object will stick back out through the inside of the tire, re-puncturing the tube and then as that section of the tire loses contact with the ground the object conceals itself again. It's almost like a bee's stinger.

First thing I would do is just slap another tube in the tire. If you have another flat in the same place then you might have something still stuck in the tire that isn't immediately obvious. If you know how the tire was oriented against the tube, inspect both the inside and the outside of the tire around where you think the puncture occurred. Do it under bright light and look for small cuts in the tread. Use a pick or tweezers to dig around in any cuts you find to ensure that nothing is hiding in there. If you find something, great! Problem solved. If not it may be coincidence.

I'm also an advocate of patching the inside of tires after anything more than a pinhole puncture. If you have a cut that is more than a millimeter or two, you probably want to boot the tire. Otherwise you've got a weak spot where debris is more likely to penetrate the tire and pop another tube. You can buy tire boots, which are expensive, or you can use the glue type (not glueless) tube patches. I've had great success with tube patches on the inside of tires, even with road tires and mtb tubeless setups. Keep in mind that this wont work on cuts bigger than a few millimeters.

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If you try and remember to always put the tire in the same place relative to the tire (line it up with the manufacturer's logo, sidewall marks, whatever) it's a little easier to find the location even with the tube pulled. Also, my patch kit has a one dollar bill in it; if I have to field patch I usually fold that up to fit and stick it between the tube and the tire where the flat happened. It's gotten me home a few times with a piece of glass still stuck in the tire. –  lawndartcatcher Feb 13 '12 at 17:41
    
Keeping the tire lined up with the wheel helps pinpoint the location the puncture occurred. Sometimes I have found the spot with nothing seen or felt, but then I shove a safety pin through the hole and something falls out!! I always have a safety pin on me, usually on my belt loop or through the inside of my pants... –  BillyNair Jun 12 '12 at 4:14
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I've had good luck shining a flashlight onto the tire as I inspect it. Little bits of debris that are nearly invisible under normal lighting become instantly visible under direct illumination. This is particularly true if the culprit is glass.

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Don't forget to rule out a spoke or spoke nipple as the cause.Check the liner for any spots that look like they may have worn thin. With mass produced wheels a tool mark on the nipple may be the cause.

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In addition to the other good answers, I'd recommend checking the rim and rim-strip as well. Tubes can "twist" inside the tire, and the puncture may not be lining up with the tube, but with something on the rim.

Look for burrs on the rim, places where the rim seam has shifted a bit to make a rough edge, thin spots on the rim strip, or the possibility that the rim strip was shifted to the side, exposing a bit of a spoke nipple.

A pinch flat is also a possibility, particularly if the tire was a bit on the low side. Pinch flats often have two tiny punctures side by side, called a "snake bite" puncture.

If you don't find anything, mount it back up and ride - the puncturing object may be long gone, and good riddance!

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If you can't find anything, and you've been cycling off-road or up and down curbs, then it could be a pinch flat. They occur when you hit something and the tyre compresses so much that the inner tube gets squashed between the rim of your bike and the object you hit.

This can cause a hole in the tyre. More often though, this kind of puncture looks like a small slit rather than a dot. And sometimes they're called snake-bite punctures because you can sometimes get two holes, one from the rim on each side of the tyre.

If this is what's happened, there won't be anything to find.

This kind of puncture is pretty common when mountain biking - I've had my share :)

The only other thing I'd suggest, is try checking the outside of the tyre too. It could be something pointy that pressed through into the inner-tube, but then because of the elasticity of the tyre rubber, got pulled back out a bit. It could be sitting in the tread of your tyre and not be poking through, but it'll be waiting to push through again, the next time you roll over that bit of the tyre!

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Well, I was doing some cycling in the city and I discovered the hole after having the bike standing for 3 hours while shopping. –  Paul Weber Feb 12 '12 at 20:56
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Another method for checking the inside of your tire is to use panty hose instead of your finger. Panty hose is very effective at snagging on things like thin bits of wire and small thorns. And also, you won't slice your finger on whatever it is that's stuck in your tire.

And like Rory said in another answer, if you can't find anything, it's probably not there any more.

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Now I just have to shop for pantyhose ... bit.ly/yK8lbL But thanks, that will go into my repair kit. –  Paul Weber Feb 12 '12 at 19:40
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That works out -- I can shop for the pantyhose at the same time I shop for the "mini-pads" I use in my helmet to absorb the sweat. –  Daniel R Hicks Feb 12 '12 at 19:51
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Cotton balls also work for finding the foreign object. –  keithmo Feb 12 '12 at 21:31
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If you have run your finger round the inside and outside and you haven't found it in the tire, and you have also checked it isn't in the beading, then it most likely fell out at some point - either while you were cycling, or when you removed the tire.

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