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  1. #1
    Email for new group DnvrFox's Avatar
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    OK

    This is from the front wheel of my trainer bicycle. In November, I patched a flat (patch is still good), and remounted the wheel on the trainer, pumped up to 120 psi. Neither trainer nor wheel has moved. Last week, flat tire. Today I removed the front tire and found this 2 inch cut. 700x25 tube. Pretty new. Tire is near new. This is an easy tire to mount, and I use no tools in remounting it, only my hands. Checked carefully for proper tube seating, as I always do.



    So, what is going on here? Rim tape is great. This cut is on the bottom of the tube. Trainer has not been moved in any way. I have sat on the trainer for several hours while training.



    Any thoughts?
    Last edited by DnvrFox; 01-12-06 at 10:44 AM.
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  2. #2
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    Quote Originally Posted by DnvrFox
    OK

    This is from the front wheel of my trainer bicycle. In November, I patched a flat (patch is still good), and remounted the wheel on the trainer, pumped up to 120 psi. Neither trainer nor wheel has moved. Last week, flat tire. Today I removed the front tire and found this 2 inch cut. 700x25 tube. Pretty new. Tire is near new.

    So, what is going on here? Rim tape is great. This cut is on the bottom of the tube. Trainer has not been moved in any way. I have sat on the trainer for several hours while training.

    Any thoughts?
    It is not clear to me whether you had the opportunity to ride the repaired tire, i.e., did it flat out before you had a chance to ride it??

    In any event, at close inspection it seems that the spoke nipple ends are protruding a bit into the tube, creating weak points along the tube's belly side. It may be that the nipples protruded a bit more in the area of the split creating a couple of weak spots which eventually split open.
    If you inflate to 90 psi this may reduce the chance of that happening. Rims built for such high pressures usually have the nipples countersinked into the rim so that even with no tape the tube does not contact the spoke nipples.

  3. #3
    Email for new group DnvrFox's Avatar
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    Quote Originally Posted by berts
    It is not clear to me whether you had the opportunity to ride the repaired tire, i.e., did it flat out before you had a chance to ride it??

    In any event, at close inspection it seems that the spoke nipple ends are protruding a bit into the tube, creating weak points along the tube's belly side. It may be that the nipples protruded a bit more in the area of the split creating a couple of weak spots which eventually split open.
    If you inflate to 90 psi this may reduce the chance of that happening. Rims built for such high pressures usually have the nipples countersinked into the rim so that even with no tape the tube does not contact the spoke nipples.
    Thanks.

    No, I did not ride it. I only sat on the trainer.

    At my weight, 90 psi is too low. But your theory is interesting, as this is a cheap bike and a cheap wheel.

    I have had the bike 2 years, and it has about 1,500 actual riding miles in addition to its use as a trainer. It is my "2nd" roadie - my "utility" roadie.

    I have had no previous "flat" problems, except. of course, goathead thorns.
    Last edited by DnvrFox; 01-12-06 at 11:18 AM.
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  4. #4
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by DnvrFox
    Thanks.

    No, I did not ride it. I only sat on the trainer.

    At my weight, 90 psi is too low. But your theory is interesting, as this is a cheap bike and a cheap wheel.

    I have had the bike 2 years, and it has about 3,000 actual riding miles in addition to its use as a trainer. It is my "2nd" roadie - my "utility" roadie.

    I have had no previous "flat" problems, except. of course, goathead thorns.
    Those indentations on the tube do look like spoke marks. was the tear on the inside, by the spokes, or out by the tyre? Looking at the shape of the indents- it is outside by the tyre, but those indents should not be there.
    On cheaper wheels, the Rim Tape band is just thin ribber strips and they are not any good. better quality is neoprene but even these do take some careful fitting. The type I use is a dense foam that sticks to the Rim and covers the well of the rim and the spokes.

    The only thing I can think of is that the rim tape band is not good enough, allowing the spokes to protude through the band and cause abrasions on the tube. The high pressure is one of the factors of this but is not a problem I experience at 60 PSI. Except when the cheap rubber protectors are used.
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    Dnvr, that is a well known failure.

    You didn't remount the tire correctly OR the tube was stuck under the tire bead OR the rim liner is covering up a portion of the hook bead.

    The result of this is that the tire lifted up and allowed the tube to expand OUTSIDE of the tire which caused it to explode.

    The tire then may or may not have collapsed back down into the rim so that there was no evidence of the cause.

    In any case it was from the tire lifting. Occasionally the lifting and the force of the explosion will break the tire bead. But the broken tire bead is NOT the cause of the problem. Jobst Brandt has experimented by cutting the tire bead in a half dozen places around a tire's perimeter and then remounting it and filling it with air. The tire did not lift off of the hook bead rim.

    I suppose it's possible that you don't have a hook bead rim but I've personally never seen a clincher rim that old.

  6. #6
    Email for new group DnvrFox's Avatar
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    Thanks, Stapfam

    I like your idea of too low a quality of rim tape. The current rim tape IS a rubber strip, much like a stretched inner tube.

    As I don't want to have a 2 inch cut while riding, I will give consideration to upgrading the rim tape. Hey, I might even be able to justify a new wheel set.
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  7. #7
    Email for new group DnvrFox's Avatar
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    Quote Originally Posted by cyclintom
    Dnvr, that is a well known failure.

    You didn't remount the tire correctly OR the tube was stuck under the tire bead OR the rim liner is covering up a portion of the hook bead.

    The result of this is that the tire lifted up and allowed the tube to expand OUTSIDE of the tire which caused it to explode.

    The tire then may or may not have collapsed back down into the rim so that there was no evidence of the cause.

    In any case it was from the tire lifting.
    OK

    Thanks Cyclintom

    I am pretty cautious about reseating the tube and checking for tube protrusion. I had not given a thought to the rim liner covering up the the hook bead!

    Okay, it is mounted back on the trainer with a new tube. I will await the results of a couple of more months on the trainer.
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  8. #8
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by DnvrFox
    Thanks, Stapfam

    I like your idea of too low a quality of rim tape. The current rim tape IS a rubber strip, much like a stretched inner tube.

    As I don't want to have a 2 inch cut while riding, I will give consideration to upgrading the rim tape. Hey, I might even be able to justify a new wheel set.

    The make of tape that I use is VELOX. French by the way. I have found that this is good enough for even the very cheap wheels that have the Spoke nipples unprotected and protrude into the Tube area, but On at Mountain bike pressures, so perhaps a pair of custom wheels are on the way. Custom wheels are not that expensive.
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  9. #9
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    i thought of improper tire mounting - but then how could you get it up to 120 psi and sat on it if the tube was torn during mounting?

  10. #10
    Senior Member BlazingPedals's Avatar
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    It's about 95% chance of having been caused by a bit of the tube sticking out under the bead, IMHO. Lining up with the inside of the tube doesn't necessarily mean a spoke problem, in this case I think it means the tube was twisted. Bad rim tape would have caused a small hole in the tube, but the tear indicates an explosion.

    I've seen seating problems go for hundreds of miles with only a slight wavering of the tread as it's ridden to warn the rider of impending doom.

    The other 5% chance is a blowout of the cord in the tire, and it's a low probablility because that should be pretty easy to see.

  11. #11
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    In my experience (and the LBS agrees with me) ANY tire pressure over 100 psig is NOT for rubber rim-strips. Either use a Velox cloth strip or (if you have V-rims) use some VeloPlugs by Velocity. The rubber rim strip is just too stretchy and will deform at higher pressures.

    Having said this, I agree that from the photo it looks like you had a tube pinch.

  12. #12
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by BlazingPedals
    It's about 95% chance of having been caused by a bit of the tube sticking out under the bead, IMHO. Lining up with the inside of the tube doesn't necessarily mean a spoke problem, in this case I think it means the tube was twisted. Bad rim tape would have caused a small hole in the tube, but the tear indicates an explosion.
    Got to disagree on a logical line of deduction. If the tube was fitted on a different line from the original by trapping the tube under the bead, there would be 2 lines of indents where it was twisted, and there is only one line of 2 sets of indents that follow the same line. Those indents by the way- I have seen these on a new tube on a new wheel on a bike I built up for a neighbour at only 40psi. I decided to check the rim tape, as I had replaced them for the owner on his previous bike. As for the length of the split-This is how most tyres go at pressure from even the smallest fault put in it (As by spoke abrasion or even Flint damage).

    I may be wrong but I don't want to change my name to Sherlock Either. Mind you, I think Watson might be interesting.
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  13. #13
    Let's do a Century jppe's Avatar
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    While I don't think I've ever had a tube split like this one, I would agree that Velox cloth rim tape is really good stuff. I had a rubber or plastic rim tape on my every day wheels and had a frequent series of flats that the cloth rim tape fixed. Most of my punctures were smaller holes.

    I was really surprised to see the nipple indentations in the tube above-I would guess that good rim tape would solve that. It's a cheap experiment anyway.

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