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  1. #1
    Muscle bike design spec robtown's Avatar
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    Tire blowout , this time 700 rim

    I just picked up a 1987/8 Schwinn with 700 rims. Since the otherwise good gumwalls had a couple dry rot spots on them I installed folding 700x23 tires rated to 125psi. The front tire blew out the side at 115 psi. After a very carefull reinstall it seemed fine. The rear tire seemed to seat properly and inflate to 120psi. After the maiden 10min ride and a 25mph descent, it blew out the side.
    The Weinman rims seem to have a mild hook. I'm wondering what to check - maybe some sort of rim defect? Would non-folding tires with metal beads work better? I'm a clydesdale at 215lbs but I could live with 100 psi / 110 psi front/back if necessary.
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  2. #2
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    Quote Originally Posted by robtown
    I just picked up a 1987/8 Schwinn with 700 rims. Since the otherwise good gumwalls had a couple dry rot spots on them I installed folding 700x23 tires rated to 125psi. The front tire blew out the side at 115 psi. After a very carefull reinstall it seemed fine. The rear tire seemed to seat properly and inflate to 120psi. After the maiden 10min ride and a 25mph descent, it blew out the side.
    The Weinman rims seem to have a mild hook.
    I suppose you've checked for the obvious. If any part of the tube is caught between the rim and any part of the tire bead the tube will blow.
    Do you have good rim tape, like Velox?
    Not familiar with your rims.
    Your weight is not the problem.

    Al

  3. #3
    surly old man jgedwa's Avatar
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    hmmm. I had this happen to me twice recently. both times with kevlar beaded tires. Perhaps they did not seat properly. perhaps a bit a tube was protruding. I think that neither of these was the case, however. Both blew very soon after I aired them up. One shreaded the tube (which admittedly does suggest that a bit of tube protruded).


    Are kevlar beads prone to this?

    j

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    I have a Paramount OS 2 from the early 1990s. No matter what the tires say the rims are not designed to go ever about 100/110 psi. If you use a micrometer on the the rim you can actually watch it bend open as the pressure goes up. I am 6 foot tall and weight close to 200 lbs and never run more that 100/110 in any of my bikes. High pressure is kind of a racers myth. I someplace have a study done by Bicycling magazine in the 1990s that basically said the higher the pressure the more flats you will have. Roger

  5. #5
    Muscle bike design spec robtown's Avatar
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    Quote Originally Posted by Al1943
    I suppose you've checked for the obvious. If any part of the tube is caught between the rim and any part of the tire bead the tube will blow.
    Do you have good rim tape, like Velox?
    Not familiar with your rims.
    Your weight is not the problem.
    Al
    I had bought new rim tape but the wheel had two layers of the black rubber strips that were clean and properly seated.
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  6. #6
    Muscle bike design spec robtown's Avatar
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    Quote Originally Posted by rhenning
    I have a Paramount OS 2 from the early 1990s. No matter what the tires say the rims are not designed to go ever about 100/110 psi. If you use a micrometer on the the rim you can actually watch it bend open as the pressure goes up. I am 6 foot tall and weight close to 200 lbs and never run more that 100/110 in any of my bikes. High pressure is kind of a racers myth. I someplace have a study done by Bicycling magazine in the 1990s that basically said the higher the pressure the more flats you will have. Roger
    I'll probably try 100/110 psi front/rear. I may try some wire bead tires - I have some a friend borrowed but did not use that I bought earlier. The current folding ones don't have much strength to the bead area. I do like a couple folding tire brands; it would be too bad if I couldn't use them. Of course, it's not worth a blowout even if it doesn't cause a spill.
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    I agree, some of the older rims were not designed to handle the higher pressures now so common. I have had similar problems w/ tires/wheels on some of my "vintage" bikes, so I have to keep the pressures in the 90-100 range when riding on the older wheels, and use the higher pressures in bikes with "newer" rims.

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    Quote Originally Posted by jgedwa

    Are kevlar beads prone to this?

    j
    No.

  9. #9
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    Quote Originally Posted by jgedwa
    hmmm. I had this happen to me twice recently. both times with kevlar beaded tires. Perhaps they did not seat properly. perhaps a bit a tube was protruding. I think that neither of these was the case, however. Both blew very soon after I aired them up. One shreaded the tube (which admittedly does suggest that a bit of tube protruded).
    The tube doesn't even need to protrude. If even a very small part of the tube is caught between the tire bead and the rim tape, or bottom of the rim, a blowout will follow, and it can be several miles down the road.

    Al

  10. #10
    Muscle bike design spec robtown's Avatar
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    I tried some wire bead 700 x 25 tires and they started lifting from rim at 85 psi. I suspect there is a rim defect. The sidewall is rubbed shiny nearby. The front wheel seems to be find at 100psi.
    Looks like a new freewheel hub wheel or wheelset. Bike just doubled in cost.
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  11. #11
    Just a wrench....
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    Quote Originally Posted by rhenning
    High pressure is kind of a racers myth. I someplace have a study done by Bicycling magazine in the 1990s that basically said the higher the pressure the more flats you will have. Roger
    I'm not sure I agree with this statement. My first impression is to say that higher pressure will give you LESS flats. A high pressure tire is less prone to pinch flats because it is going to be harder to compress the tire onto the rim, pinching it.

    I could be wrong, as flats are a mystery to most people. Anyone have any evidence one way or the other?

  12. #12
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    I was quoting Fred Matheny and Jim Langley former editiors at Bicycling magazine. I consider them both friends and heard them again say it at Lon Haldemans Coaching Week during his Desert Camp in Arizona last Winter. The three of them have web sites and if you do a Google search you will find them. Roger

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    Quote Originally Posted by ikaraus
    I'm not sure I agree with this statement. My first impression is to say that higher pressure will give you LESS flats. A high pressure tire is less prone to pinch flats because it is going to be harder to compress the tire onto the rim, pinching it.

    I could be wrong, as flats are a mystery to most people. Anyone have any evidence one way or the other?
    "Higher" and "lower" are pretty subjective terms. I think running pressures pretty close to the tire's maximum recommended pressure is the best practice when trying to balance rolling efficiency, handling, ride, and flat avoidance. I run my rear tire right at max recommended and the front about 10 psi lower than the front.

    Al

  14. #14
    Just a wrench....
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    Quote Originally Posted by rhenning
    I was quoting Fred Matheny and Jim Langley former editiors at Bicycling magazine. I consider them both friends and heard them again say it at Lon Haldemans Coaching Week during his Desert Camp in Arizona last Winter. The three of them have web sites and if you do a Google search you will find them. Roger
    That's not exactly the explination I was looking for. Just because some editors I have never heard of say it is true, doesn't make it.

    I'll look on google for their article, but certanly if your friends say it you must know WHY it is true, and not just blindly believe. Like I said I could be way off base, I have never done a scientific experiment to determine the exact effects, but it seems that my idea is logical. I'd just like a real explination one way or the other if someone has facts.

    And to the other poster, by high pressure I meant close to or at the max limit of the tire. I run mine right up there.

    ---edit------

    After a quick google I found nothing to support lower pressure = less flats. Linked are the artilces by your experts. If anything it says keep pressure.

    "The Right Pressure Makes a Big Difference
    Most people put too little pressure in road tires and too much pressure in off-road rubber. Road tires usually take from 95 to 125 pounds per square inch (psi). If you weigh less than 150 pounds, go toward the lower end and vice versa. For mountain tires intended for off-road use, a good range is from 35 to 45 pounds. Use the same rule for weight. With off-road rubber, you’ll find that less air means a softer ride and improved control because the tire has a larger footprint on the trail."
    http://www.jimlangley.net/crank/basicstuff.html#trp

    "Check inflation pressure every couple of days. Tubes are slightly porous and may lose several pounds of pressure each day. Soft tires slow you down, corner poorly, wear fast, and don’t protect your rims against metal-bending impacts."
    http://www.planetultra.com/training/...adhazards.html
    Last edited by ikaraus; 09-27-06 at 08:45 AM.

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