Innertube Porosity?

Discussion in 'Cycling Equipment' started by Steve Sr., Dec 29, 2005.

  1. Steve Sr.

    Steve Sr. Guest

    I was wondering if anyone has any information on the porosity of
    various kinds / brands of innertubes. By porosity I mean the very slow
    leakdown rate that occurs with sound tubes over days and weeks. You
    know... The reason you are always topping up your tires to prevent
    pinch flats.

    My current interest is any differences between the regular and
    "lightweight" road tubes of the same size. I am also wondering if
    "brand" makes any difference as well.

    Thanks,

    Steve
     
    Tags:


  2. Tom Keats

    Tom Keats Guest

    In article <[email protected]>,
    Steve Sr. <[email protected]> writes:
    > I was wondering if anyone has any information on the porosity of
    > various kinds / brands of innertubes. By porosity I mean the very slow
    > leakdown rate that occurs with sound tubes over days and weeks. You
    > know... The reason you are always topping up your tires to prevent
    > pinch flats.
    >
    > My current interest is any differences between the regular and
    > "lightweight" road tubes of the same size. I am also wondering if
    > "brand" makes any difference as well.


    Y'know, I've had tubes of the same brand with different seepage rates.
    So IMO, the particular brand may not be a useful quantifier.
    There may be a variation from batch to batch with tubes from
    the same manufacturer (or factory.) There may even be a variation
    within batches.

    I believe getting an especially air-retaining or an especially
    air-losing tube boils down to the luck of the draw.

    In general, tubes made from natural latex are lighter than butyl
    tubes, and are somewhat more porous[*]. Perhaps the weather
    conditions at the rubber plantations might cause some variation
    in the quality of batches of latex tubes? I dunno -- maybe how
    closely latex or butyl tubes are stored to the ship's generators
    (or other cargo whose out-gassings might react with "rubber")
    en route from China might affect their quality too.


    cheers,
    Tom

    [*] http://www.sheldonbrown.com/tires.html

    --
    -- Nothing is safe from me.
    Above address is just a spam midden.
    I'm really at: tkeats [curlicue] vcn [point] bc [point] ca
     
  3. Steve Sr. writes:

    > I was wondering if anyone has any information on the porosity of
    > various kinds / brands of inner tubes. By porosity I mean the very
    > slow leakdown rate that occurs with sound tubes over days and weeks.
    > You know... The reason you are always topping up your tires to
    > prevent pinch flats.


    > My current interest is any differences between the regular and
    > "lightweight" road tubes of the same size. I am also wondering if
    > "brand" makes any difference as well.


    I doubt that anyone has numbers but you could buy one and see if you
    can put up with its inflation demands. That is what counts isn't it?
    I never liked daily pumping of tubulars with latex tube especially
    because we did that with a Silca frame fit pump. It is one of the
    things that inspired me to design a two stage pump.

    Jobst Brandt
     
  4. Sandy

    Sandy Guest

    Dans le message de news:[email protected],
    [email protected] <[email protected]> a
    réfléchi, et puis a déclaré :
    > Steve Sr. writes:
    >
    >> I was wondering if anyone has any information on the porosity of
    >> various kinds / brands of inner tubes. By porosity I mean the very
    >> slow leakdown rate that occurs with sound tubes over days and weeks.
    >> You know... The reason you are always topping up your tires to
    >> prevent pinch flats.

    >
    >> My current interest is any differences between the regular and
    >> "lightweight" road tubes of the same size. I am also wondering if
    >> "brand" makes any difference as well.

    >
    > I doubt that anyone has numbers but you could buy one and see if you
    > can put up with its inflation demands.


    From its November 2005 issue :

    Winner overall : Décathlon butyl (1,5€)
    Loser overall : Challenge latex (10€)

    The results combined the attributes of leakage, weight, valve connection,
    ease of installation, fragility, uniformity and price. For full results and
    the charts, you may want to pick up a copy. This is addressed to a
    world-wide English reading audience, although the narrative of the article
    is only in French. The numbers, however, stick to the usual Arabic based
    characters we all use. Sorry that the pricing is in euros.

    --
    Sandy
    Verneuil-sur-Seine
    *******

    La vie, c'est comme une bicyclette,
    il faut avancer pour ne pas perdre l'équilibre.
    -- Einstein, A.
     
  5. Joe Riel

    Joe Riel Guest

    I notice the opposite effect, which I find curious. That is, a
    completely deflated inner tube, with its valve (presta) tightly
    closed, partially reinflates after several days if it is not tightly
    compressed. That is, when I attempt to roll it back up I have to
    again loosen the valve to let out some air. What causes this? Is it
    leakage at the valve? This occurs on more than one brand of butyl
    inner tube.

    Joe
     
  6. Matt O'Toole

    Matt O'Toole Guest

    On Thu, 29 Dec 2005 21:56:00 -0500, Steve Sr. wrote:

    > I was wondering if anyone has any information on the porosity of various
    > kinds / brands of innertubes. By porosity I mean the very slow leakdown
    > rate that occurs with sound tubes over days and weeks. You know... The
    > reason you are always topping up your tires to prevent pinch flats.
    >
    > My current interest is any differences between the regular and
    > "lightweight" road tubes of the same size. I am also wondering if "brand"
    > makes any difference as well.


    There's certainly a difference, but I've never noted exactly how much. Of
    course latex tubes need to be pumped every day. Lightweight butyl tubes
    maybe every 3-4 days, and regular tubes once a week or less.
    Besides the difference between lightweight and regular tubes, there are
    differences between brands. Some are thicker than others.

    When I buy tubes, I worry more about valves, and how easily the tube can
    be patched. These days I buy only Michelin tubes, because the valves
    never leak, the pump seals well, and there's minimal
    flashing/seams to interfere with patching. Either the regular
    "Airstop" or lightweight models are fine.

    Matt O.
     
  7. Paul Hobson

    Paul Hobson Guest

    Joe Riel wrote:
    > I notice the opposite effect, which I find curious. That is, a
    > completely deflated inner tube, with its valve (presta) tightly
    > closed, partially reinflates after several days if it is not tightly
    > compressed. That is, when I attempt to roll it back up I have to
    > again loosen the valve to let out some air. What causes this? Is it
    > leakage at the valve? This occurs on more than one brand of butyl
    > inner tube.
    >
    > Joe


    Tubes lose air because they are under high pressure relative to the
    atmosphere, which causes diffusion from the tube back to its
    surroundings. If you push out all of the tube and seal it, now the
    atmosphere is at a higher pressure than the tube. So it would make
    sense that air would diffuse back into the tube, right?

    --
    Paul M. Hobson
    Georgia Institute of Technology
    ..:change the f to ph to reply:.
     
  8. Leo Lichtman

    Leo Lichtman Guest

    "Paul Hobson" wrote: (clip) So it would make sense that air would diffuse
    back into the tube, right?
    ^^^^^^^^^^^^^^^^
    Doubtful. It would be virtually impossible to squeeze a tube enough to
    force ALL the air out. Since the walls are flexible, the pressure in the
    tube will be equal to the atmospheric pressure outside it. Possibly the
    tube is put away cold, and then warms up afterward, causing the air inside
    to expand. Could it be that the rubber "outgasses," releasing a little air
    after the tube is deflated?
     
  9. jim beam

    jim beam Guest

    Steve Sr. wrote:
    > I was wondering if anyone has any information on the porosity of
    > various kinds / brands of innertubes. By porosity I mean the very slow
    > leakdown rate that occurs with sound tubes over days and weeks. You
    > know... The reason you are always topping up your tires to prevent
    > pinch flats.
    >
    > My current interest is any differences between the regular and
    > "lightweight" road tubes of the same size. I am also wondering if
    > "brand" makes any difference as well.
    >
    > Thanks,
    >
    > Steve


    there's two factors: one is actual porosity, the other is diffusion.
    rubbers are subject to both, with the former being a factor of quality,
    the latter is natural and can't be stopped. [condom production is a
    fine example of porosity control.] for quality, stick to name brands
    and look for country of manufacture.

    for air, butyl rubber offers the best air diffusion/mechanical
    properties ratio, hence it's common use.
     
  10. Paul Hobson

    Paul Hobson Guest

    Leo Lichtman wrote:
    > "Paul Hobson" wrote: (clip) So it would make sense that air would diffuse
    > back into the tube, right?
    > ^^^^^^^^^^^^^^^^
    > Doubtful. It would be virtually impossible to squeeze a tube enough to
    > force ALL the air out. Since the walls are flexible, the pressure in the
    > tube will be equal to the atmospheric pressure outside it. Possibly the
    > tube is put away cold, and then warms up afterward, causing the air inside
    > to expand. Could it be that the rubber "outgasses," releasing a little air
    > after the tube is deflated?


    well yeah. I didn't mean that one would create a vacuum. But if you
    fold a tube, push it flat, then seal the valve, it'll be under a
    negative gage pressure. That's all I was trying to say. The
    temperature-driven scenario is definitely plausible - especially if you
    have to change a tube on the road this time of year. No clue on the
    outgassing though.

    \\paul
    --
    Paul M. Hobson
    Georgia Institute of Technology
    ..:change the f to ph to reply:.
     
  11. jim beam

    jim beam Guest

    Joe Riel wrote:
    > I notice the opposite effect, which I find curious. That is, a
    > completely deflated inner tube, with its valve (presta) tightly
    > closed, partially reinflates after several days if it is not tightly
    > compressed. That is, when I attempt to roll it back up I have to
    > again loosen the valve to let out some air. What causes this? Is it
    > leakage at the valve? This occurs on more than one brand of butyl
    > inner tube.
    >
    > Joe


    diffusion/porosity works both ways. elasticity of the tube will create
    a [minimally] lower pressure inside an evacuated tube, so there's no
    reason air won't migrate to reestablish equilibrium.
     
  12. Paul Hobson

    Paul Hobson Guest

    Paul Hobson wrote:
    > Leo Lichtman wrote:
    >
    >> "Paul Hobson" wrote: (clip) So it would make sense that air would
    >> diffuse back into the tube, right?
    >> ^^^^^^^^^^^^^^^^
    >> Doubtful. It would be virtually impossible to squeeze a tube enough
    >> to force ALL the air out. Since the walls are flexible, the pressure
    >> in the tube will be equal to the atmospheric pressure outside it.
    >> Possibly the tube is put away cold, and then warms up afterward,
    >> causing the air inside to expand. Could it be that the rubber
    >> "outgasses," releasing a little air after the tube is deflated?

    >

    [snip[

    > The
    > temperature-driven scenario is definitely plausible - especially if you
    > have to change a tube on the road this time of year. No clue on the
    > outgassing though.


    If you change a tube, it probable has a hole in it. Sorry (I'm still on
    vacation)

    \\paul
     
  13. Someone

    Someone Guest

    Sandy wrote:
    >
    > From its November 2005 issue :
    >
    > Winner overall : Décathlon butyl (1,5€)
    > Loser overall : Challenge latex (10€)


    INDEFINITE PRONOUN ALERT!

    What is "its"?

    --
    Tom Sherman - Fox River Valley
     
  14. Werehatrack

    Werehatrack Guest

    On 30 Dec 2005 18:15:22 -0800, "Someone" <[email protected]>
    wrote:

    >
    >Sandy wrote:
    >>
    >> From its November 2005 issue :
    >>
    >> Winner overall : Décathlon butyl (1,5€)
    >> Loser overall : Challenge latex (10€)

    >
    >INDEFINITE PRONOUN ALERT!
    >
    >What is "its"?


    A possessive pronoun with no direct one-to-one corresponding
    equivalent in French.
    --
    Typoes are a feature, not a bug.
    Some gardening required to reply via email.
    Words processed in a facility that contains nuts.
     
  15. A Muzi

    A Muzi Guest

    > Joe Riel wrote:
    >> I notice the opposite effect, which I find curious. That is, a
    >> completely deflated inner tube, with its valve (presta) tightly
    >> closed, partially reinflates after several days if it is not tightly
    >> compressed. That is, when I attempt to roll it back up I have to
    >> again loosen the valve to let out some air. What causes this? Is it
    >> leakage at the valve? This occurs on more than one brand of butyl
    >> inner tube.


    Paul Hobson wrote:
    > Tubes lose air because they are under high pressure relative to the
    > atmosphere, which causes diffusion from the tube back to its
    > surroundings. If you push out all of the tube and seal it, now the
    > atmosphere is at a higher pressure than the tube. So it would make
    > sense that air would diffuse back into the tube, right?


    Agree. I think the unspoken bit here is that some tubes are
    'flatter' or 'rounder' than others. If you cut out the
    valve, what cross section does it display? Tubes which lie
    flat in that test would be less likely to expand when left
    laying around I think than tubes which 'want' to be round in
    cross section.

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  16. Joe Riel

    Joe Riel Guest

    A Muzi <[email protected]> writes:

    >> Joe Riel wrote:
    >>> I notice the opposite effect, which I find curious. That is, a
    >>> completely deflated inner tube, with its valve (presta) tightly
    >>> closed, partially reinflates after several days if it is not tightly
    >>> compressed. That is, when I attempt to roll it back up I have to
    >>> again loosen the valve to let out some air. What causes this? Is it
    >>> leakage at the valve? This occurs on more than one brand of butyl
    >>> inner tube.

    >
    > Paul Hobson wrote:
    >> Tubes lose air because they are under high pressure relative to the
    >> atmosphere, which causes diffusion from the tube back to its
    >> surroundings. If you push out all of the tube and seal it, now the
    >> atmosphere is at a higher pressure than the tube. So it would make
    >> sense that air would diffuse back into the tube, right?

    >
    > Agree. I think the unspoken bit here is that some tubes are 'flatter'
    > or 'rounder' than others. If you cut out the valve, what cross section
    > does it display? Tubes which lie flat in that test would be less
    > likely to expand when left laying around I think than tubes which
    > 'want' to be round in cross section.


    Here's some idle speculation. What drives air molecules through the
    rubber? Diffusion? Does the rate of gas diffusion through a material
    depend on pressure?

    In an inflated tube, constrained by the tire, the rubber of a properly
    sized inner tube is in compression. That implies that any pores in
    the rubber should be closed tighter than they would be if the tube
    were not inflated. If the rate of diffusion is not dependent on the
    pressure of the gas (independent of the compression), then the rate
    should be slower as the pressure increases because the compression is
    increasing, causing the pores to close. That would imply that the
    rate is greatest with an uninflated tube.

    Not sure I believe any of that...maybe someone who knows something
    about this can enlighten me.

    Joe Riel
     
  17. A Muzi

    A Muzi Guest

    >>>Joe Riel wrote:
    >>>>I notice the opposite effect, which I find curious. That is, a
    >>>>completely deflated inner tube, with its valve (presta) tightly
    >>>>closed, partially reinflates after several days if it is not tightly
    >>>>compressed. That is, when I attempt to roll it back up I have to
    >>>>again loosen the valve to let out some air. What causes this? Is it
    >>>>leakage at the valve? This occurs on more than one brand of butyl
    >>>>inner tube.


    >>Paul Hobson wrote:
    >>>Tubes lose air because they are under high pressure relative to the
    >>>atmosphere, which causes diffusion from the tube back to its
    >>>surroundings. If you push out all of the tube and seal it, now the
    >>>atmosphere is at a higher pressure than the tube. So it would make
    >>>sense that air would diffuse back into the tube, right?


    > A Muzi <[email protected]> writes:
    >>Agree. I think the unspoken bit here is that some tubes are 'flatter'
    >>or 'rounder' than others. If you cut out the valve, what cross section
    >>does it display? Tubes which lie flat in that test would be less
    >>likely to expand when left laying around I think than tubes which
    >>'want' to be round in cross section.


    Joe Riel wrote:
    > Here's some idle speculation. What drives air molecules through the
    > rubber? Diffusion? Does the rate of gas diffusion through a material
    > depend on pressure?
    >
    > In an inflated tube, constrained by the tire, the rubber of a properly
    > sized inner tube is in compression. That implies that any pores in
    > the rubber should be closed tighter than they would be if the tube
    > were not inflated. If the rate of diffusion is not dependent on the
    > pressure of the gas (independent of the compression), then the rate
    > should be slower as the pressure increases because the compression is
    > increasing, causing the pores to close. That would imply that the
    > rate is greatest with an uninflated tube.
    >
    > Not sure I believe any of that...maybe someone who knows something
    > about this can enlighten me.


    Yes I believe tubes permeate air to a greater or lesser
    extentwith afew variables liek material, wal thickness,
    pressure.
    To your comment about the tube being 'in compression', don't
    you think in most cases a bigger factor is that the tube is
    simply larger in use when it fills the space inside the casing?

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  18. Paul Hobson

    Paul Hobson Guest

    Someone wrote:
    > Sandy wrote:
    >
    >>From its November 2005 issue :
    >>
    >>Winner overall : Décathlon butyl (1,5€)
    >>Loser overall : Challenge latex (10€)

    >
    >
    > INDEFINITE PRONOUN ALERT!
    >
    > What is "its"?
    >


    Look at the the subject line of your own post :)

    (she's referring to Le Cycle)

    --
    Paul M. Hobson
    Georgia Institute of Technology
    ..:change the f to ph to reply:.
     
  19. Sandy

    Sandy Guest

    Dans le message de news:[email protected],
    Paul Hobson <[email protected]> a réfléchi, et puis a déclaré :
    > Someone wrote:
    >> Sandy wrote:
    >>
    >>> From its November 2005 issue :
    >>>
    >>> Winner overall : Décathlon butyl (1,5€)
    >>> Loser overall : Challenge latex (10€)

    >>
    >>
    >> INDEFINITE PRONOUN ALERT!
    >>
    >> What is "its"?
    >>

    >
    > Look at the the subject line of your own post :)
    >
    > (she's referring to Le Cycle)


    Please do not tamper with my gender !
    --
    Bonne route !

    Sandy
    Verneuil-sur-Seine FR
    --
    Les faits relatés ici ne sont que pure fiction, et ne sauraient être
    utilisés ou rapprochés d'une situation réelle existant ou ayant
    existée
     
  20. Someone

    Someone Guest

    Paul Hobson wrote:
    > Someone wrote:
    > > Sandy wrote:
    > >
    > >>From its November 2005 issue :
    > >>
    > >>Winner overall : Décathlon butyl (1,5€)
    > >>Loser overall : Challenge latex (10€)

    > >
    > >
    > > INDEFINITE PRONOUN ALERT!
    > >
    > > What is "its"?
    > >

    >
    > Look at the the subject line of your own post :)


    I also assumed that the source was Le Cycle, but the source should have
    been stated in the text.

    --
    Tom Sherman - Fox River Valley
     
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