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intepreting a tube puncture

Old 11-10-20, 01:36 AM
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btppberk
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intepreting a tube puncture

I had a tube puncture today on my road bike tube's inner seam, almost exactly in the middle of the tube's contact with the rim. I checked the rim and didn't see or feel anything suspicious. It seems a bit too centered to be pinch flat. I was running 25s on a 15C rim (inner width) at 90 psi and hadn't hit anything particularly pinching in the road. Any ideas?
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Old 11-10-20, 01:44 AM
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Originally Posted by btppberk View Post
. Any ideas?
if it looks like a spoke poke, it probably was a spoke poke, even if you swear the rim tape is unpoked... another layer of tape on top should do it.
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Old 11-10-20, 04:43 AM
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Inspect your rim tape. If it is anything other than adhesive rim tape, replace it with an adhesive rim tape.
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Old 11-10-20, 09:17 AM
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Pinch flats are usually characterized by two holes next to each other (also called snake eyes).
If the hole was at a spoke location, that could be a clue or point to the spoke as a suspect.
Otherwise, it's anybody's guess. For example, perhaps a foreign object embedded itself in the area during your last tube change.
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Old 11-10-20, 09:19 AM
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Agree with others, inner tube seam hole is usually spoke related. I always use the Velox tape, note it comes in different widths.
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Old 11-10-20, 10:53 AM
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Originally Posted by MudPie View Post
Pinch flats are usually characterized by two holes next to each other (also called snake eyes).
Snake bite is a more appropriate description - two punctures close to each other.
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Old 11-10-20, 01:13 PM
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Thanks all. I will double check the tape and tape over it with another layer. Much appreciated.
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Old 11-10-20, 11:43 PM
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Originally Posted by aggiegrads View Post
Snake bite is a more appropriate description - two punctures close to each other.
Right you are! Snake bite (not snake eyes).
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Old 11-11-20, 02:09 AM
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Spoke or sharp rim edge, if using double-wall rims. Rubber rim strips "sink" into the spoke holes, exposing the spoke hole edges on the rim and wear through your tube. Don't use rubber or cheap, flimsy nylon tape (often an OEM item to save $). The Velox rec is spot on.
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Old 11-11-20, 12:35 PM
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Having patched 90 tubes for my co-op recently and given that it has been a constant problem in my own tubes, I don’t agree that punctures on the inside are due to the tube extending into the spoke hole. That kind of mini-blowout is easy to spot. The tube has a very distinct damage and look. 25 to 30% of the tubes I patched had punctures along in the inside edge. I’ve been seeing a similar rate for my own flats. The holes are very small like most of the punctures I’ve seen. I use Velox tape in my own wheels and there is no deformation of the tape nor holes in the tape. Perhaps it’s due to debris in the rim but I have yet to find any in my wheels.

The problem seems to be greater with narrower tubes used in wider tires. I used to carry 23mm tubes and use them in 32 to 35mm to save the weight of carrying a larger tube. The tube expands to fill the space and I’ve been doing this for the better part of 25 years without issue. The holes don’t look like the tube has split but I wonder if that is what is happening. It also seems to be happening with newer tubes. The rubber of tubes today doesn’t seem as flexible as old tubes were. They just can’t seem to expand as much and the tube breaks at a weak point.

Another hypothesis I have is that the tube may be twisting in the tire, especially for very thin tubes. If you inflate a tube outside of a tire, they can sometimes invert so that the outer edge of the tube is inside the torus. Perhaps this is happening with narrow tubes in wide tires so that the puncture is actually on the outside (inner edge) but appears on the inside when the tube is deflated.

The first idea seems more probably.
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Old 11-11-20, 06:00 PM
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Originally Posted by cyccommute View Post
Having patched 90 tubes for my co-op recently and given that it has been a constant problem in my own tubes, I donít agree that punctures on the inside are due to the tube extending into the spoke hole. That kind of mini-blowout is easy to spot. The tube has a very distinct damage and look. 25 to 30% of the tubes I patched had punctures along in the inside edge. Iíve been seeing a similar rate for my own flats. The holes are very small like most of the punctures Iíve seen. I use Velox tape in my own wheels and there is no deformation of the tape nor holes in the tape. Perhaps itís due to debris in the rim but I have yet to find any in my wheels.
Can you explain why doubling up on the Velox solves the problem? (in my case anyway) I had no indication that the first layer had lost any integrity... it seems like the stuff can get poked through and heal itself.
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Old 11-11-20, 06:28 PM
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Originally Posted by DiabloScott View Post
Can you explain why doubling up on the Velox solves the problem? (in my case anyway) I had no indication that the first layer had lost any integrity... it seems like the stuff can get poked through and heal itself.
Iíve never needed to double the Velox. In todayís tight tires (so that they are tubeless ready), that would make fitting the tires even more difficult. I havenít had this problem nearly as much in the past with just a single layer of Velox. I even used to suggest using 23mm tubes in large diameter tires...up to 35 mm...to save weight and make them easier to carry spares. But over the last 5 or so years, Iíve seen lots and lots of punctures on the inner side.
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Old 11-11-20, 07:38 PM
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A few weeks ago, I was using a 38 mm tire, so I got the appropriate sized tube, 700 x 35-43. And it promptly split open along the inside seam. Twice, in completely different spots. I started a thread about and got mostly insults:

What a Defective Inner Tube Looks Like

Meanwhile, thanks to all the "help" I got in that thread, I just went ahead and used a very thin 20-25c inner tube, on the same 38 mm tires, and have had zero problems.

Therefore, from my experience, going to a wider tube did not work. I honestly think there's something wrong with these tubes causing them to split open.
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Old 11-11-20, 10:16 PM
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I double-checked the spokes and couldn't detect a problem, but I'll use Velox thanks to your recommendations.

Your comments raised another question for me: I have also been getting punctures (including today) on the inside maybe 30 or 45 degrees from the seam. I've had this happen a few times. I had presumed I am pinch flatting due to running a 25C on a 15C inner-width rim. But the holes are all single: no snake bites. Probably still a pinch flat?

Thanks again for your help--much appreciated.
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Old 11-11-20, 11:33 PM
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Originally Posted by cyccommute View Post
The problem seems to be greater with narrower tubes used in wider tires.
I came to the same conclusion, and now prefer tubes that are closer to the size of the tire. The way I figure, a skinny tube in a wide tire is not only stretched out more, but is also simply thinner.
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Old 11-13-20, 08:24 AM
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When I've been faced with this sort of puncture, I can usually solve it by running a single layer of fiber reinforced packing tape around the rim, followed by cloth rim tape. Two layers of cloth rim tape is too thick in some cases.
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