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What the heck happened to my tube?

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What the heck happened to my tube?

Old 01-20-22, 07:10 PM
  #1  
BkSurly
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What the heck happened to my tube?

Here are the clues:

-I cant post a picture yet, but there is neat half-inch tear along the innermost seam in the tube, the side that contacts the rim tape.
-Brand new surly midnight special with factory tubes that I've ridden for 50 miles, 650x47 tires.
-No noticeable impacts on my most recent ride--put the bike away with inflated tires, and found that the tire was flat the next day.
-No noticeable damage to the tire or rim
-If the tire pressure gauge on my pump is accurate, I was running about 5psi under the maximum for the tires.
Thank you for helping me solve this mystery.
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Old 01-20-22, 07:24 PM
  #2  
tyrion
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Originally Posted by BkSurly View Post
...there is neat half-inch tear along the innermost seam in the tube, the side that contacts the rim tape.
That's happened to me and I don't know what caused it. Maybe simply a defective tube.

I'd go tubeless - I think the stock tires and rims are tubeless compatible, so all you need is tubeless rim tape, tubeless valves, and sealant.
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Old 01-20-22, 07:30 PM
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DiabloScott
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Was the tire bead off the rim when you found it flat? That would indicate a blowout, and that would probably be an installation error that didn't show up until recently... weird, but it happens.

If not, the tire was just flat but the bead seat was good - that would probably indicate a tube defect... weird but that happens too.
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Old 01-20-22, 08:01 PM
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I had a tube puncture just like that. I noticed the edge of the rim tape was sticking up, and the rim tape is fairly stiff as well. I guess over time, with enough rubbing , the edge of the rim tape cut through the tube. I redid it with wider tape which spans the full width of the inside of the rim, and doesn't stick up. It seems to be working fine so far.
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Old 01-20-22, 09:21 PM
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Tubes fail for any number of reasons. Some mysteries aren't worth trying to solve unless it happens a few times. If I were you, I'd go tubeless anyway.
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Old 01-21-22, 08:55 AM
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I wrote the following after suffering a huge number of flats in Michigan this summer

Originally Posted by cyccommute View Post
I might have agreed even a few months ago. However, nearly every flat I’ve experienced over the last year have been on the interior of the tube…i.e. the rim side. I’ve changed rim strips from cloth Velox just in case there was something in the tape. I marked the tube with direction arrows and clocked my tubes to the label. Nothing seemed to work. I still experienced internal pinhole flats.

About a month ago, I went through flat hell in Wisconsin and Michigan while on tour. I experienced 8 to 10 flats of exactly the same kind including 4 in a single day. One of them was on one of the few really nice downhills in the U.P. in Michigan. I did a quick dodge around rumble strips to get out into the lane rather than do 20+ mph on a very narrow shoulder. The picture below is typical of Michigan’s rumble strips.


I experienced a blow out…which is very scary on a loaded touring bike at normal speed and petrifying at high speed. When I took the tire off, there was a rip on the inside of the tube about an inch long. After changing my bike shorts (), a light bulb went off. There is no way that I could have had anything inside the tire that would cause the tube to actually rip. I eventually decided that what had happened was that the quick steering to avoid the rumble strips had allowed the tube to be pulled too far in one direction. The rubber was obviously thin on the rim side and it tore due to the extra force on the rubber.

I have, in the past, been a proponent of using smaller tubes. They are lighter to carry and rubber expands to fill the space. I didn’t, however, take into account something that I’ve noticed when pumping up a tube outside of the tire. Tubes tend to expand more on the outside of the torus that is the tube than on the inside of the torus. If the tube were a straight pipe, the pressure expansion would look a bit like this (please excuse the extremely simple drawings). The pressure would expand equally in all directions and the tube (pipe, actually) would expand equally in all directions.



But in a torus shape, the outside edge expands slightly more than the inner edge like in the diagram below. The inner edge doesn’t have room to expand as much as the outer edge…it packs up a bit more. You can observe this when you pump up the tube outside of the tire.



Now think of the tube in the rim, especially if the tube is a smaller sized tube. When the tube is put in the tire and filling is started, the tube expands towards the tire first. Then as the tube fills, it expands into the rim channel. The outer part of the tube is trapped against the tire and the inner part has to expand into the channel where it thins. I suspect (but can’t really prove) that the tube thins a lot and, rather than the tube being punctured, the tube tears and creates a pin hole.



My solution was to replace my 23/28mm tubes with 38/44mm tubes. The wider tubes had more material in the channel and were less prone to tearing. The proof of this idea was that my inner punctures disappeared at about the 1/2 way point of my 1200 mile tour.

Going forward, I’m going to stop using small diameter tubes and use wider ones.
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Old 01-21-22, 09:34 AM
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Did you stop immediately when you flatted, or did you ride on the rim for a while. The tear might be something you got while coasting to a stop after the flat happened.
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Old 01-21-22, 09:50 AM
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Cyccommute's analysis that large tubes are less stressed inside a tire is correct. Using the largest tube that will fit is a good idea with the downside that they are more difficult to install and heavier.

To the OP: I have the same Midnight Special with the same size 650b wheels and WTB Horizon 650bx47 tires. My wheels are Shimano GRX WH-RX570 tubeless ready, not the Surly supplied ones. I am running these tubeless with Muc-Off sealant at about 45 psi and they have been very good so far. The overall set up is significantly lighter than using inner tubes since tubes that size are very heavy and the worry about pinch flats is gone. When I first got the bike I had 700c wheels and 700x32 tires with inner tubes and suffered two pinch flats in less than 1000 miles even with the tires at 65 psi. To allow larger tires without increasing the standover height (which was marginal at the time), I substituted the 650b wheels and tires and went tubeless. It's worked out well and I recommend you consider it.
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Old 01-22-22, 09:50 AM
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Originally Posted by DiabloScott View Post
Was the tire bead off the rim when you found it flat? That would indicate a blowout, and that would probably be an installation error that didn't show up until recently... weird, but it happens.
The tire wouldn't need to be off the rim for this to happen. If the tire was installed with some of the tube trapped under the tire bead, it could blow out in exactly this way and leave the tire seated on the rim.
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Old 01-23-22, 10:08 AM
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Great info on using a larger tube!!

I never would have thought of that.!!

Thanks for sharing !!!
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Old 01-24-22, 08:14 AM
  #11  
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I would add that for the vast majority of us regular riders, a tear in a tube is a pretty rare occurrence (touch wood) using regular or slightly undersized tubes, so don't get too concerned about this example.

and there always the possibility that rough use of a tire lever could have damaged/weakened this tube at some point, who knows.
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