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  1. #1
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    Presta valves on Bontrager thorn-resistant tubes

    I've got an ongoing problem that I'm hoping someone could enlighten me about. I'm a X-country rider on very gently sloping and smooth DG fans in Arizona, nothing gonzo about the terrain other than the cacti. Recently I've been using Bontrager thorn-resistant Presta tubes (that's what my shop carries) and for the 4th time in as many rides the entire Presta valve assembly promptly rips itself right out of the tube on my rear wheel, resulting in an instantaneous ride-ending flat (bummer). Since it seemed that maybe both the tire and tube are 'moving' on the rim, I've marked the tire's position on the rear wheel before rides and confirmed that in fact the tire repositions itself about 3/4" forward on the wheel relative to its starting position. I'll assume this means that friction between the tube and tire is dragging the tube along with it, resulting in the Presta valve separating from the tube; seems logical anyway. What I can't understand is why this problem seems to occur only with the Bontrager tubes and not (yet) with several other brands I've used over the years. I always seat the valve stem fully vertically with the silver locknut cinched up firmly against the rim hole, and ride with ~ 45 psi (I weigh 190 lbs). This morning I tried using yet another brand-new Bontrager thorn-resistant Presta tube in a brand-new Hutchinson Python tire, but before mounting it on the rim I coated the tube and inside of the tire with talcum powder to try and reduce friction. Result: yet another ripped-out Presta valve after 20 minutes of riding. I've talked with the guys at my shop and they suggested it might have been a 'bad batch' of tubes so they replaced them out with some from a newer batch, but they're still a problem for me. These tubes get expensive after awhile with this problem, so you can see I'm anxious to find a solution. Can anyone out there pass along some ideas? Thanks much.

  2. #2
    NMBP/OMBA crew!
    Reputation: Strykar's Avatar
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    Mar 2007
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    check to make sure your using the right size tire for your rim width.
    http://ocalabicyclecenter.com/


    Rubber side down is good for me

  3. #3
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    Quote Originally Posted by StealthBoy
    Since it seemed that maybe both the tire and tube are 'moving' on the rim, I've marked the tire's position on the rear wheel before rides and confirmed that in fact the tire repositions itself about 3/4" forward on the wheel relative to its starting position. I'll assume this means that friction between the tube and tire is dragging the tube along with it, resulting in the Presta valve separating from the tube; seems logical anyway.
    Instead of trying to reduce the friction between the tube and the tire, why not try to keep the tire from slipping on the rims? Is there any chance a soap of some kind got on the rims when you were washing the wheels? Maybe you could try giving the rims a thorough wiping down with a moist cloth to see if you can get rid of any oil/soap to get some stiction between it and the tire.

    Just as a side note, if you mount your tires so the name of the tire is on the exact opposite side of the name of the rims you can sight down on a set of wheels and tell exactly what set of tires is on a set of rims in one look. A professionally built set of wheels will have the name of the hubs on the opposite side of the name of the rims for the same reason. You can then also tell if there was any movement of the tires on the rims in the future.

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