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  1. #1
    Halocon
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    tire or inner tube?

    i've been wondering about this for quite a while now... is it the inner tube that determines how much air pressure or is it the tire? im thinking it's the tire since the tire is what has stuff written on it stating what the max psi is. but doesn't the inner tube have a limit too?

  2. #2
    Senior Member
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    Its primarily the tire and the rim together.

  3. #3
    You need a new bike supcom's Avatar
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    The limitation on maximum air pressure is determined by the strength of the tire. The cords in the tire must withstand the pressure. The rim and tire bead play a part in that too much pressure could potentially pull the bead away from the rim and expose the tube.

    The tube is pressed up against the inside of the tire and rim to seal against air leaks. If the tire is the correct size, it is barely stretched and is not a factor in the maximum pressure.

  4. #4
    cyclist/gearhead/cycli... moxfyre's Avatar
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    The tube needs only to be airtight and the right size for the tire. If you take a tube and pump it up, it will expand until it explodes. However, inside the tire, the tube has not only the air pushing on it from the inside, but the tire and rim pushing on it from the outside! So it can withstand any pressure as long as the tire can support it.
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  5. #5
    sch
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    There is one proviso additionally: the tube should be the appropriate size for the tire. Using an 20-25mm
    tube in a 40-50mm tire risks failure of the tube from tearing at micro tears and scratches in the rubber
    that would not happen in a 20-25mm tire. Steve

  6. #6
    Member
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    all of the three have vital role of holding tire pressure. it must be considered how strong the three is, in order not to blow up your day.

  7. #7
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by blackshadow
    all of the three have vital role of holding tire pressure. it must be considered how strong the three is, in order not to blow up your day.
    Sure, but the strength of the inner tube material is only important if a thorn or rock punctures the tire. If nothing gets through the tire, then the tube is literally supported on all sides by the tire and rim, and cannot blow up.

    It seems unintuitive, but the pressure inside the inner tube will not damage it, because the tire is pushing back on the outside just as hard as the air is pushing on the insider. There is no net force on the walls of the properly mounted inner tube.
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