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  1. #1
    Senior Member FenderTL5's Avatar
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    Q: What happens if you screw the plastic cap on a presta valve..

    Question: What happens if you screw the plastic cap on a presta valve without closing the stem completely?
    Has anyone done this?
    Nashville, like L.A. without a tan.

  2. #2
    Senior Member RPK79's Avatar
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    If you have carbon rims they will asplode.

  3. #3
    Senior Member FenderTL5's Avatar
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    Nope, they're not carbon rims (whew!!!) they're Bontrager Nebula 32-hole rims
    I'm Just looking for a possible explanation for a weird occurrence. This crossed my mind as a possibility.
    Nashville, like L.A. without a tan.

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    Senior Member Wilfred Laurier's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    Nope, they're not carbon rims (whew!!!) they're Bontrager Nebula 32-hole rims
    I'm Just looking for a possible explanation for a weird occurrence. This crossed my mind as a possibility.
    weird occurrences are often supernatural in cause
    so i would contact a priest or shaman who has experience with bicycles and pressure vessels

  5. #5
    Senior Member RPK79's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    Nope, they're not carbon rims (whew!!!) they're Bontrager Nebula 32-hole rims
    I'm Just looking for a possible explanation for a weird occurrence. This crossed my mind as a possibility.
    Bontrager is just code for Trek so even if they're not carbon they'll likely asplode. Just be safe and throw that little plastic cap away!

  6. #6
    Senior Member FenderTL5's Avatar
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    Quote Originally Posted by Wilfred Laurier View Post
    weird occurrences are often supernatural in cause
    so i would contact a priest or shaman who has experience with bicycles and pressure vessels
    Agreed!
    I think my garage is a natural habitat for bike gnomes, who like to mess with bicycles when no one is around and/or the lights are out.
    Nashville, like L.A. without a tan.

  7. #7
    Senior Member FenderTL5's Avatar
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    Quote Originally Posted by RPK79 View Post
    Bontrager is just code for Trek so even if they're not carbon they'll likely asplode. Just be safe and throw that little plastic cap away!
    It's hard to tell if you're serious.. how would the rim explode? The pressure point for the air doesn't change. It would still be coming out of the valve. I think it could blow the little plastic cap off.. possibly?
    Nashville, like L.A. without a tan.

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    Senior Member Wilfred Laurier's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    It's hard to tell if you're serious.. how would the rim explode? The pressure point for the air doesn't change. It would still be coming out of the valve. I think it could blow the little plastic cap off.. possibly?
    i am sure rpk79 would never joke about the ongoing scourge of
    asploding carbon rims

  9. #9
    Senior Member RPK79's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    It's hard to tell if you're serious.. how would the rim explode? The pressure point for the air doesn't change. It would still be coming out of the valve. I think it could blow the little plastic cap off.. possibly?
    It's physics. Don't worry though so long as you don't have crabon fibber wheels and you replace your trek rims you won't have to worry about asplosions.

  10. #10
    Senior Member RPK79's Avatar
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    Quote Originally Posted by Wilfred Laurier View Post
    i am sure rpk79 would never joke about the ongoing scourge of
    asploding carbon rims
    Never. It's serious business.



    This was caused by leaving the valve open and putting a plastic cap on.

  11. #11
    apocryphal sobriquet J.C. Koto's Avatar
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    I suppose it's possible the cap could depress the valve and let out the air.

  12. #12
    Senior Member Homebrew01's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    Question: What happens if you screw the plastic cap on a presta valve without closing the stem completely?
    Has anyone done this?
    Try it and see. Depending on clearance, it is possible the cap would push down & release air. The manufacturer should make the caps tall enough to prevent it, but who knows ?
    Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike

  13. #13
    Senior Member RPK79's Avatar
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    Quote Originally Posted by Homebrew01 View Post
    Try it and see. Depending on clearance, it is possible the cap would push down & release air. The manufacturer should make the caps tall enough to prevent it, but who knows ?
    Wear safety glasses though.

  14. #14
    Senior Member FenderTL5's Avatar
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    Quote Originally Posted by J.C. Koto View Post
    I suppose it's possible the cap could depress the valve and let out the air.
    Quote Originally Posted by Homebrew01 View Post
    Try it and see. Depending on clearance, it is possible the cap would push down & release air. The manufacturer should make the caps tall enough to prevent it, but who knows ?
    This what I'm thinking happened. Tire was at half pressure (50lbs +/-) and the plastic cap gone. I'm thinking it released air until the cap finally launched.
    Possible, you think?
    Nashville, like L.A. without a tan.

  15. #15
    Senior Member Homebrew01's Avatar
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    Now that you know the evils of the plastic cap, you can pump up your tire without it and see what happens.
    Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike

  16. #16
    Senior Member GhostSS's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    Question: What happens if you screw the plastic cap on a presta valve without closing the stem completely?
    Has anyone done this?
    Quote Originally Posted by J.C. Koto View Post
    I suppose it's possible the cap could depress the valve and let out the air.
    I've done this on my rear tire. My tire went flat. That is all.

    Pumped it up the next morning and it was fine.

  17. #17
    Senior Member mprelaw's Avatar
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    Quote Originally Posted by FenderTL5 View Post
    Question: What happens if you screw the plastic cap on a presta valve without closing the stem completely?
    Has anyone done this?
    Can't say I ever have, myself. Mainly because of what I do with the stupid thing the minute I take a new tube out of the box.

  18. #18
    Senior Member Nermal's Avatar
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    Quote Originally Posted by Homebrew01 View Post
    Now that you know the evils of the plastic cap, you can pump up your tire without it and see what happens.
    I guess I've been left behind, again. I always pump up my tires with the cap off.
    Some people are like a Slinky ... not really good for anything, but you still can't help but smile when you shove them down the stairs.

  19. #19
    Senior Member
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    Quote Originally Posted by RPK79 View Post
    Never. It's serious business.



    This was caused by leaving the valve open and putting a plastic cap on.
    nonsense!

    it's obvious that the front wheel is in quicksand.

  20. #20
    Senior Member capejohn's Avatar
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    Just a point of information. The plastic cap's only purpose is to protect the valve from puncturing the tube during shipping and while it's in storage It looks good on our bikes but once the tube is installed, the valve cap serves no purpose and is not necessary.
    Bike riding New England gentleman.

  21. #21
    Senior Member danmc's Avatar
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    Quote Originally Posted by RPK79 View Post
    Never. It's serious business.


    I've done that before when I droped the hammer and cranked it up to 300 watts. Drove the front wheel 6 inches into the pavement. It had to be jackhammered out.

  22. #22
    Senior Member BlazingPedals's Avatar
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    Quote Originally Posted by RPK79 View Post
    Never. It's serious business.



    This was caused by leaving the valve open and putting a plastic cap on.

    Heeey... That rim didn't asplode; it just went flat.

    I think Koto has the correct answer.

  23. #23
    Senior Member RPK79's Avatar
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    Quote Originally Posted by BlazingPedals View Post
    Heeey... That rim didn't asplode; it just went flat.

    It's a classic snake-bite puncture.

  24. #24
    coprolite fietsbob's Avatar
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    the other half went pan-dimensional ..

  25. #25
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    Quote Originally Posted by RPK79 View Post
    Never. It's serious business.



    This was caused by leaving the valve open and putting a plastic cap on.

    This accident wouldn't have happened if the rider wasn't using clipless pedals!

    /I'm a jerk!

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