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What causes this?

Old 10-12-12, 08:41 PM
  #1  
Donsell
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What causes this?

This is the 2nd flat I've had caused by a series of holes. Is this a pinch flat?

Attached is a pic -

Thanks.
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Old 10-12-12, 08:56 PM
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thats pretty weird, I would take the tire completely off your rim and turn it inside out. check the interior for defects or foreign materials. also check your rim tape for funkiness. you will be able to get a general idea of where the issue is based on the alignment of the stem.
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Old 10-12-12, 09:04 PM
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Lay the tube alongside the rim with the valve lined up with the hole. That will tell you where along the rim to focus your attention. Likewise with the tire, if you still have a reference point (hint for the future; either go OCD and mount tires with a reference at the valve, or mark the valve hole after installing the tire, or before removing it to change a flat).

It's a strange damage pattern. I've seen a few instances where a piece of glass woodpeckers the tube as the tire goes flat, but never this uniformly.
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Old 10-12-12, 09:06 PM
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This is the 2nd time in a couple of weeks for this pattern. The first time was a brand new tube so I thought it was a defect. I always align my tire and haven't found anything so I wondered if I'd done something at installation.
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Old 10-12-12, 09:08 PM
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Where's the damage, tire side, rim side, or somewhere else.

The location is the best clue to the cause. If it's on the tire side, odds are it's nothing you did.
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Old 10-12-12, 09:14 PM
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Nope, it on the side, almost straight across from the valve. That's why I wondered if I pinched it installing the tire. But it didn't go flat until almost a week after I installed it.
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Old 10-12-12, 09:15 PM
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Where were you riding when you had that flat?
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Old 10-12-12, 09:17 PM
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I rode it home on my commute last night and it was fine. It was flat tonight when I went to prep my bike for tomorrow.
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Old 10-12-12, 09:24 PM
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Originally Posted by Donsell
Nope, it on the side, almost straight across from the valve. That's why I wondered if I pinched it installing the tire. But it didn't go flat until almost a week after I installed it.
Did you already examine the inside part of the tire sidewall that would touch that area of the tube? Do you have old rusty steel rims? Did you use tools to mount the tire onto the rim?
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Old 10-12-12, 09:25 PM
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Originally Posted by Donsell
Nope, it on the side, almost straight across from the valve. That's why I wondered if I pinched it installing the tire. But it didn't go flat until almost a week after I installed it.
Think back to how you installed the tire. Is the damage near to where you finished? If so it's possible you trapped it under the bead, not enough to pop off, but enough to pinch it as it pulled free at full pressure.

If it only happened once you could shrug it off as a defect of some kine. But twice means it's something in the rim, tire, or your technique.
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Old 10-12-12, 09:30 PM
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I've been all over the tire and rim. I bought the bike in July and have 1400 miles on it. It's gotta have been how I installed it. I was hoping it was typical of a pinch flat so I'd know for sure.

Thanks.
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Old 10-12-12, 09:36 PM
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Originally Posted by Donsell
I've been all over the tire and rim. I bought the bike in July and have 1400 miles on it. It's gotta have been how I installed it. I was hoping it was typical of a pinch flat so I'd know for sure.

Thanks.
The classic pinch flat that sometimes happens when you use tire levers to install, usually looks different. It's similar to what mtn bikers call a snake bite with 2 small slits paired about 1/8" apart. Imagine a tool piercing all the way through the edge of a tube folded flat.

BTW- do you pre-fill the tube to give it shape, or install it still folded flat the way it came out of the box? If the latter, try prefilling next time since it reduces the chance of pinching or trapping it under the bead.
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Old 10-12-12, 09:40 PM
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I always put some air in to make sure the tube isn't folded. I've had about 100 flats this summer, goat heads have been nasty. I did use a tool to get the last of the tire over the rim so maybe I caught it, but I rode it for almost a week before it went flat this time.
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Old 10-12-12, 09:48 PM
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Originally Posted by Donsell
I've had about 100 flats this summer.........
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Old 10-12-12, 09:52 PM
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Could that part of the tube been trapped under the bead, and the tire bead have a sharp edge that could cause that sort of pattern?
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Old 10-12-12, 11:37 PM
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Originally Posted by Donsell
I've been all over the tire and rim. I bought the bike in July and have 1400 miles on it. It's gotta have been how I installed it. I was hoping it was typical of a pinch flat so I'd know for sure.

Thanks.
The pinch flats caused by catching the tube with the lever while installing the tire usually are crescent shaped and not multiple.
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Old 10-12-12, 11:39 PM
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When looked at closely the irregularities appear far more like abrasions from multiple sources than punctures from a sharp object, even taking into account tube movement. It's interesting that they are so evenly spaced and almost exactly parallel to the seam, with a "shadow" 2nd line that has the same spacing, but with each mark offset by about half the distance between them. The only time I've seen a pattern anything like this it was from removing a tire by dragging a rought tire lever along the tire bead, but that does not seem to be a possibility here. I don't think it has anything to do with installation error - the pattern is just too "perfect." It seems far more likely to be caused by something with which the tube is usually very well aligned - either the tire or the rim.

I'm wondering if it has to do with the extreme amount of flats the OP has experienced. I would think that many mount/dismount cycles could cause some stress on the inner surface of the tire - something that one would not normally recognize as a problem but that could show up when the tube is pressing hard on the inside of the tire.

OP: I would recommend replacing the tire to see if that resolves the problem, as substitution is always a good idea when one is running out of ideas as to cause of a problem. Then take the old tire and press HARD inside, near the bead with a cotton ball, traveling around both beads, to see if anything catches. I would be interested in knowing the tire and rim combo, as well as to what pressure you inflate and how often, and finally if your route includes significant hills and whether your riding style includes fairly hard acceleration and braking. Thanks

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Old 10-13-12, 07:01 AM
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With such a distinct pattern and an alignment reference you should be able to match up the damage to the portion of the tire/rim that made it. If it is a pinch, the pattern should match some evenly spaced protrusions on either the rim or the tire at the pinch point. Pinch flats are usually more of single or double V or crescent shaped marks (sometimes referred to as snakebite). I've not seen a pinch that made such an elongated uniform pattern but close examination of the tire and rim/rimstrip and careful installation should solve that problem.

Another less likely possibility is that if both tubes were the same size and brand, you could have gotten two tubes from a bad batch. Examine the new tube carefully before installing or switch brands if you can't find anything any other cause.
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Old 10-13-12, 07:38 AM
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Almost looks like a rough tire lever that was run along the bead when removing the tire. Was that the only area leaking?
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Old 10-13-12, 07:40 AM
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I was using some hyperbole when I said I've had 100 flats. It seems like I've had a lot of them this year, but most of them have been thorns on the local limestone trails.

Its the stock tired and hub on a Scott Sportser 55. I think it's a good plan to replace the tire.
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Old 10-13-12, 11:29 AM
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Get something with some decent puncture protection. On a budget, I like Serfas tires.
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Old 10-13-12, 11:40 AM
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It's a type of pinch flat that is caused by only one sidewall doing the pinching. This sort of flat generally happens if your wheel gets caught in an edge trap, if you run across an object at a very shallow angle the sidewall of the tire gets pinched, resulting in a series of punctures. Inspect the portion of the tire where the wounded tube was located and it probably contains a scuff. You might recall having ridden off a trail or sidewalk and skipping back up. (You might have almost fallen.)

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Old 10-13-12, 12:17 PM
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Originally Posted by curbtender
Almost looks like a rough tire lever that was run along the bead when removing the tire. Was that the only area leaking?
that's exactly what I thought as soon as I saw it. I think it's either that or a section that was caught in the rim in some other manner.
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Old 10-13-12, 01:12 PM
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Originally Posted by cale
It's a type of pinch flat that is caused by only one sidewall doing the pinching. This sort of flat generally happens if your wheel gets caught in an edge trap...
That makes some sense, but the OP says the same pattern occured twice, which seems unlikely for a road hazard like that. If it was twice in the same rim location then it's pretty much out of the question as an explanation.
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Old 10-13-12, 01:27 PM
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Originally Posted by digibud
that's exactly what I thought as soon as I saw it. I think it's either that or a section that was caught in the rim in some other manner.
Looks familiar. I'm not saying that is what caused it but I have seen the same pattern on automotive tubes when the tire lever of a tire machine rubbed the tube during rotation to remove the tire from the rim. If a lever was used in a similar manner removing the bike tire it could cause the same type of abrasion.
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