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  1. #1
    Senior Member PatrickJIV's Avatar
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    Where does the air go?

    Can't understand why my tires leak air. Lose about 10#psi per month. Both tires are slime filled, valve is not leaking at all....so....where does the air go?
    Old in AGE, young @ HEART!

  2. #2
    Senior Member garysol1's Avatar
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    10psi loss per month is nothing. The air especially when under pressure simply finds its way through the rubber tube and is released. Perfectly normal.

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    Yes, there's a slow diffusion of air molecules through the walls of the rubber tubes. Heavier, thicker tubes will lose air more slowly. CO2 will diffuse through much quicker than regular air. And if you're really concerned then you could use pure nitrogen which escapes a little slower than the oxygen in the air (21% oxygen, 78% nitrogen, 1% argon and others - plus a variable amount of water vapor).

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    Porosity ... Tubes, though they hold air very effectively, seep air. Air sneaks out through the bead occassionally too going over bumps.
    10 lbs. is about avg. per month, better than.. if you frequently ride.
    I've had bikes idle for many months and had only a little loss. Others required routine topping-off. In which case, tubes were changed.
    There IS a point though where the air escapes at a reduced rate.
    Cars are a good example; less pressure (especially when u.infl.) with plenty of volume. Bikes have Hi-Press, low volume. Golf Carts have neither.
    If you routinely kept your bike tires too low, they would lose less.

  5. #5
    Senior Member PatrickJIV's Avatar
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    Very informative answers from all, and I thank everyone!
    Old in AGE, young @ HEART!

  6. #6
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    Ive taken tubes from cheap bikes. checked them in a bucket of water for leaks.
    the tubes take on a silvery sheen as theres lots of cracks in the tube. where the airs escaping. Its not big enough holes to do big bubbles that escape quickly.

  7. #7
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    Quote Originally Posted by old and new View Post
    Air sneaks out through the bead occassionally too going over bumps.
    Only if you use tubeless tires. Innertubes don't leak from bumps unless they are severe enough to cause a "snakebite" puncture.

    Quote Originally Posted by old and new View Post
    There IS a point though where the air escapes at a reduced rate. Cars are a good example; less pressure (especially when u.infl.) with plenty of volume.
    The other thing car tires have is a much longer diffusion path since the tread and side walls are much thicker than a bike innertube. The further the air molecules have to go the slower they diffuse out.

  8. #8
    My bike's better than me! neil0502's Avatar
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    It's a well-known fact that the air goes to Fresno, California.

    HTH.

  9. #9
    Back on Bikes at 53!
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    All very good reasons why one shouldn't simply apply test results of how nitrogen works in car tires, to bicycle tires.

    Bicycles tires have: 1. A much smaller volume of air for the rubber surface area
    2. Thinner rubber
    3. Higher pressures, except perhaps for the largest "balloon" type tires

    For myself, all my bike tires are in the 35-47mm range, 80psi tops in the rears, I just pump up with air. If I had nitrogen around for some other reason, I'd use it, but won't go to the trouble & expense just for the bikes

  10. #10
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    Quote Originally Posted by PatrickJIV View Post
    Can't understand why my tires leak air. Lose about 10#psi per month. Both tires are slime filled, valve is not leaking at all....so....where does the air go?
    A 10 pound loss in a couple of days is normal for high pressure road bike tires. They need to be fully inflated before each ride.

    Al

  11. #11
    Senior Member SlimAgainSoon's Avatar
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    10-lbs. a month -- a lose more air than that in a week.

    You must have good tubes.

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