Positioning of valve when pumping your tire
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  1. #1
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    Positioning of valve when pumping your tire

    Always wondered bit never asked…

    Does it matter if the valve is at the top or bottom position of the tire when filling it? Is there a difference in the psi readout on the gauge?

    I know I can just test it but I am not home and thought I’d find out before I got home…but wait, I’m taking a flight directly after work and not going home so I won’t be able to test this for the next few days. Drat! I need an answer.
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  2. #2
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    usually put the valve in the 12 o'clock position (top of wheel, valve head pointing down)...easier to reach that way.

    but, I purchased some cheap tubes online recently that require that they be at 6 o'clock because the chuck doesn't seat firmly on them and tends to blow off when hanging from the 12 o'clock position..

    there should be no difference in pressure readout, regardless of valve position.
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  3. #3
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    Does it matter
    .....
    no

    Just out of curiosity, what was the scientific "theory" that led you to think there might be an effect?
    Last edited by JCavilia; 11-22-2011 at 11:10 AM.

  4. #4
    The Pb Torpedo
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    Air has such a low density that it does not matter.

    (There is an infinitesimally small effect.)

    Trust me... I'm a scientist.

  5. #5
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    Quote Originally Posted by TWB8s View Post
    The valve usually points toward the hub
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  6. #6
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    The valve usually points toward the hub

  7. #7
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    If you're running any fluid (e.g. tubeless with sealant) you don't want the stem at the 6 o'clock position, unless you want to clean up a mess.

  8. #8
    The Pb Torpedo
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    Quote Originally Posted by TWB8s View Post
    The valve usually points toward the hub
    This response is most worthy.

  9. #9
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    Gravity causes more air to accumulate at the bottom of the tire, thus increasing the psi in that position. Therefore it's best to put the valve at either the 9 or 3 o'clock position before filling. With more air at the bottom, the riding is also smoother because there's more air where the tire contacts the road, thus providing more traction and comfort.
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  10. #10
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    Quote Originally Posted by Special Eyes View Post
    Gravity causes more air to accumulate at the bottom of the tire, thus increasing the psi in that position. Therefore it's best to put the valve at either the 9 or 3 o'clock position before filling. With more air at the bottom, the riding is also smoother because there's more air where the tire contacts the road, thus providing more traction and comfort.
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    No, it makes no difference. If you need to prove it to yourself, fill the tire in a 12 o'clock, then with the floor pump still attached move the tire to 6 o'clock and compare pressures.

    Best,
    C.

  11. #11
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    I'm thinking there's a general lack of understanding about pressure in this here thread....
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    Still, it felt great and I felt like I was sitting on some kind of vibrator -Touch0Gray

  12. #12
    The Pb Torpedo
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    Quote Originally Posted by Cedric View Post
    If you need to prove it to yourself, fill the tire in a 12 o'clock, then with the floor pump still attached move the tire to 6 o'clock and compare pressures.
    Bold added above.

    Just be careful to avoid any or all of the fork, seat stay, chain, chain stay, other part of chain, etc., when moving the tire from 12 to 6.

  13. #13
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    All things considered equal... there's no difference.

    However, with one of my pumps it's easier to inflate the tire properly with the valve at 6 o'clock. When at 12 o'clock the weight of the hose seems to angle the pump head just enough to effect the flow of air a bit. When at 6 o'clock the hose lays on the floor and this doesn't happen.

    I can get to the proper PSI either way. It's just easier if the valve is at 6 o'clock.
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  14. #14
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    You need to rotate the wheel when filling so the air is equally distributed around the tire. Otherwise, it will be out of balance.

  15. #15
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    Quote Originally Posted by seacoaster View Post
    You need to rotate the wheel when filling so the air is equally distributed around the tire. Otherwise, it will be out of balance.
    Dumbest thing I ever heard! Everyone knows that centrifugal force will distribute the air equally as soon as you start to ride!

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  16. #16
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    Quote Originally Posted by RJP Diver View Post
    Dumbest thing I ever heard! Everyone knows that centrifugal force will distribute the air equally as soon as you start to ride!

    Yeah right! As if?? If that were true I wouldn't have a small flat spot on the bottom when I was riding. There is obviously less air on the bottom, it is not equally distributed as you suggest.
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  17. #17
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    Oh sure, the pressure may not matter, but you had better make certain you fully deflate the tube before adding fresh air. That stale stuff will do terrible things to your tubes...

  18. #18
    TheCyclingActor
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    .........just put air in your tire and ride your damn bike.

  19. #19
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    Quote Originally Posted by RJP Diver View Post
    All things considered equal... there's no difference.
    This is one of the most universal truths in the universe, other universes not withstanding.

    I love this forum!

  20. #20
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    Position. 10 to 2 o'clock.

    I always put the valve up top-ish so I can more easily hold it steady with one hand if necessary and to make sure it has a good locked-in fit. I have in the past caused alot of valve rip-age by the valve moving around radically as I pumped away.

  21. #21
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    Does it matter if the valve is at the top or bottom position of the tire when filling it? Is there a difference in the psi readout on the gauge?
    Yes it obviously makes a difference due to the change in altitude between the top & bottom of the wheel. Therefore to get a true accurate average pressure reading the valve must be either at 3 or 9 o'clock.
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  22. #22
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    Can't wait until this thread takes on hydroplaning!!!

  23. #23
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    Quote Originally Posted by old'n'slow View Post
    Oh sure, the pressure may not matter, but you had better make certain you fully deflate the tube before adding fresh air. That stale stuff will do terrible things to your tubes...
    Actually the stale air itself does no harm to the tubes, it's when you mix fresh air with the stale air that the damage begins.
    But yeah, the old air does need to be removed just like you said.

  24. #24
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    If you run tubeless with sealant, locate the valve sten up high. Less chance of spray back. I am used to this method now and while only one of my bikes is tubeless and technically requires this, it's easier (less leaning over) if all the valves are up as high as possible so that's what I do on all my bikes. I'm sure that other than running with sealant in the tire, it doesn't make any real difference other than what I stated.

  25. #25
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    Quote Originally Posted by velodog View Post
    Actually the stale air itself does no harm to the tubes, it's when you mix fresh air with the stale air that the damage begins.
    But yeah, the old air does need to be removed just like you said.
    Wow. In a thread filled with dumb, there's always got to be a winner.

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    Everybody knows that good ol' fashioned air is mostly nitrogen.

    Therefore, everybody knows that if you keep just topping off, eventually you'll have all nitrogen, and therefore the fastest, highest-tech bicycle on the planet.
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