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  1. #1
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    Are under-sized tubes okay?

    I recently had to replace a bad tube on my bike and went to the LBS to get another backup. I have 700x28 tires and was looking for another one that had a threaded stem, but they didn't have any in that size. The shop owner told me I could use a 700x18/20 tube and it would be fine; he said it would actually be easier to install. I can't shake this feeling though that's too undersized for the size tire I have... is it? Even if it's okay, now I'm concerned that my CO2 cartridges would probably be too much for that size of tube (I believe it would put 120psi into a 700x28 tube).

    Thanks

  2. #2
    blah blah blah milkbaby's Avatar
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    Pump the tube up outside of a tire. You'll see that it can inflate to about three times it's unstretched size. The tire holds the tube inside, so that doesn't matter. It will work fine.

  3. #3
    Thread Killer
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    Yeah it'll just be a little bit thinner at installed size than a larger tube, and a little more susceptible to punctures and pinch flats, but not a lot, I think. I wouldn't worry, anyway.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

  4. #4
    Senior Member SpeshulEd's Avatar
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    You'll be fine. I've used road tubes in 2" mtb tires before when I was in a pinch.
    Hey guys, lets go play bikes!

    Strava

  5. #5
    Senior Member
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    The limiting factor is the interior size of the tire. That determines the pressure generated by a given quantity of inflating gas. So same oressure no matter what size the tube is if the tire is the same. I have used 52 g 19-25 mm tubes in a 23 mm tire. Surely your undersized tube in a larger tire won't be any thinner than that.

  6. #6
    Senior Member Homebrew01's Avatar
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    Going to extremes, I would worry about streeses where the valve attaches to the tube.
    1 way to find out.
    Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike

  7. #7
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    You'll be fine. I've done the same many times.
    You're just trying to start an argument to show how smart you are.

  8. #8
    Has opinion, will express
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    I ride 23C spec tubes in 32C tyres all the time, and have done so for years. No flats, no blowouts, no problems directly attributable to the tubes.

    One of the reasons I use 23C tubes is that they are much cheaper in bulk lots from the vendor I use.
    Dream. Dare. Do.

  9. #9
    Junior Member willhenry's Avatar
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    Slightly higher chance of flats. Not a big problem.

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