getting flats at the valve- Mtbr.com
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  1. #1
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    getting flats at the valve

    Recently since switching to new rims and presta valves, i've had multiple flats from the tube separating from the base of valve. The tubes were all the same brand that flatted, but they were kenda so i would trust their product. What could be causing these flats?
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  2. #2
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    Quote Originally Posted by Gsromich View Post
    Recently since switching to new rims and presta valves, i've had multiple flats from the tube separating from the base of valve. The tubes were all the same brand that flatted, but they were kenda so i would trust their product. What could be causing these flats?
    The most common cause of valve stem separation is running tire pressure too low. If the pressure is too low it can allow the tire so slip on the rim. The tire and tube both being rubber the tube tends to move with the tire and eventually will pull the stem out of the tube. The fix is to add a few psi. What psi do you normally run?

    Another common problem can be the rim tape used. The cheap plastic rim tape that comes with some rims can be rather sharp in the area of the stem hole and wear through the rubber around the valve causing it to tear. The fix is to go with Velox cloth rim tape.

    Other not so common causes are, burs or sharp edges around the stem hole. Simple fix is a round fine jewelers file to smooth the metal. Or you could have a rim that is actually drilled for a Schrader valve or has been modified to use a Stans tubeless conversion kit. In this case the inner valve hole would be too large and not support the area around the valve stem and allow it to protrude into the hole and tear the rubber. In the case of an actual schrader rim you have two choices, run a shrader valve tube, or get a presta adapter, a small bit that slides into the hole and tightens up the tolerance to presta spec. In the case of a tubeless mod, simply using a good cloth rim tape should solve the problem.

    Anyway, those are some things to check out.

    Good Dirt
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  3. #3
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    Alright thanks for the info. I usualy ride at about 30 psi in my front 2.3 nevengall and a little bit more on the rear 2.1 bontranger. When the wheelset came it did not include rim strips so i bought the velox cloth rim strips. I have a different tube in the front now that has a lockring on the valve to secure on the outside of the rim, so maybe this will help.
    "A day without sunshine is like, you know, night."
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  4. #4
    Jason
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    Another problem with Prestas that I've seen is people over-tightening the lock ring. I've seen them tightened so much that the lock ring rips the tube.
    Jason
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    The bicycle; the noble invention that saves my health, inside...and out.

  5. #5
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    Make sure that you apply some powder to the tubes to help them not move if you tyre is moving. Make sure the beads of your tyres and rim are clean and have no grease on them that may help them to slip. I had some XM 117 Mavics that I had this problem with, but when I moved to the XM321s never had the issue again, never really checked to see what caused it, but as Squash said, could have been the rim tape having sharps edges or the actual rim having burrs.
    Quote Originally Posted by Harold
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