Rim tolerance (runout) Question

Discussion in 'Cycling Equipment' started by Rob Weinstock, Apr 17, 2004.

  1. How flat should a new rim be?

    I recently received a set of NOS rims in the mail. The box had obvious
    shipping damage. When I hold the two rims together, brake surface to
    brake surface, it's clear that one or both has some damage. However,
    it is slight, only about 3mm of daylight appear between the rim edges,
    which I can close with an easy squeeze of my fingers. Running my
    fingers around the rim reveals no flats, creases, or other damage that
    would make me automatically toss the rim.

    So, is 3mm flat enough to result in a wheel that will have "even
    enough" spoke tension? These are 36-hole Mavics, BTW.

    Thanks and regards,

    Rob
     
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  2. daveornee

    daveornee Guest

    Rob Weinstock wrote:
    > How flat should a new rim be?
    > I recently received a set of NOS rims in the mail. The box had obvious
    > shipping damage. When I hold the two rims together, brake surface to
    > brake surface, it's clear that one or both has some damage. However, it
    > is slight, only about 3mm of daylight appear between the rim edges,
    > which I can close with an easy squeeze of my fingers. Running my fingers
    > around the rim reveals no flats, creases, or other damage that would
    > make me automatically toss the rim.
    > So, is 3mm flat enough to result in a wheel that will have "even enough"
    > spoke tension? These are 36-hole Mavics, BTW.
    > Thanks and regards,
    > Rob




    You can likely bend the rim(s) back flat. If they are some of the more
    compliant Mavics it can be done by "hand" . It is difficult to know what
    the spoke tension story will be until after you build them up. I have
    built Sun rimmed wheels where the rims started flat to less than 0.05mm
    and round to the same tolerance, but the rim wouldn't stay true to
    within 0.5 mm when completed and tension balanced. If you are in a
    situation of not easily returning them for a replacement, what other
    alternatives were you considering? The methods described in Jobst
    Brandt's book "the Bicycle Wheel" will work. Just take your time and use
    an accurate "flat" for a standard.



    --
     
  3. Rob Weinstock writes:

    > How flat should a new rim be?


    > I recently received a set of NOS rims in the mail. The box had
    > obvious shipping damage. When I hold the two rims together, brake
    > surface to brake surface, it's clear that one or both has some
    > damage. However, it is slight, only about 3mm of daylight appear
    > between the rim edges, which I can close with an easy squeeze of my
    > fingers. Running my fingers around the rim reveals no flats,
    > creases, or other damage that would make me automatically toss the
    > rim.


    By that description, you should have no trouble building good wheels
    with these rims. Don't bother doing anything to them other than
    putting a dab of oil on the inside of each eyelet (there where the
    spoke nipple will bear) and build wheels.

    Jobst Brandt
    [email protected]
     
  4. > You can likely bend the rim(s) back flat. If they are some of the more
    > compliant Mavics it can be done by "hand" . It is difficult to know what
    > the spoke tension story will be until after you build them up. I have
    > built Sun rimmed wheels where the rims started flat to less than 0.05mm
    > and round to the same tolerance, but the rim wouldn't stay true to
    > within 0.5 mm when completed and tension balanced. If you are in a
    > situation of not easily returning them for a replacement, what other
    > alternatives were you considering? The methods described in Jobst
    > Brandt's book "the Bicycle Wheel" will work. Just take your time and use
    > an accurate "flat" for a standard.


    Thanks for the response -- finding an accurate flat will be
    interesting. I have a granite inspection stone, but it's only 18" x
    12". Garage floors are notorious not flat.

    These are vintage NOS rims, Mavic Record du Monde. Very pretty. My
    choices are to use as-is; try my luck with an insurance claim; chuck
    and try to find another; attempt to fix, then use.

    I'm wondering how flat/round rims are from the factory? I mean, are
    there standardized specs that are maintained, etc.?

    Thanks and regards,

    Rob
     
  5. > By that description, you should have no trouble building good wheels
    > with these rims. Don't bother doing anything to them other than
    > putting a dab of oil on the inside of each eyelet (there where the
    > spoke nipple will bear) and build wheels.


    Thanks, that's reassuring.

    Regards,

    Rob
     
  6. daveornee

    daveornee Guest

    Rob Weinstock wrote:
    > > By that description, you should have no trouble building good wheels
    > > with these rims. Don't bother doing anything to them other than
    > > putting a dab of oil on the inside of each eyelet (there where the
    > > spoke nipple will bear) and build wheels.

    > Thanks, that's reassuring.
    > Regards,
    > Rob




    Ritchey says "* High Tolerance Machined (+0.03mm)" for many of their
    rims. I have seen similar results in Mavic rims and Velocity rims
    although I have never see what they specify.



    --
     
  7. A Muzi

    A Muzi Guest

    >>You can likely bend the rim(s) back flat.
    -snip-

    Rob Weinstock wrote:
    finding an accurate flat will be
    > interesting. I have a granite inspection stone, but it's only 18" x
    > 12". Garage floors are notorious not flat.

    -snip-
    > I'm wondering how flat/round rims are from the factory? I mean, are
    > there standardized specs that are maintained, etc.?


    Lay it on a true wheel.
    Press it flat before you build it
    New Rims arrive within a millimeter

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  8. Andrew Muzi writes:

    >>> You can likely bend the rim(s) back flat.


    >> Finding an accurate flat will be interesting. I have a granite
    >> inspection stone, but it's only 18" x 12". Garage floors are
    >> notorious not flat.


    >> I'm wondering how flat/round rims are from the factory? I mean,
    >> are there standardized specs that are maintained, etc.?


    > Lay it on a true wheel. Press it flat before you build it New Rims
    > arrive within a millimeter


    Pressing a rim against a flat surface will not remove wows that are
    within the elastic limit of the rim. That means, greater than +-10mm.
    As I said, if the rim is a smooth saddle then forget the wow and build
    the wheel. That sort of misalignment is trivial to flatten and will
    not affect performance. Kinks are another matter but I don't see that
    a new rim will have kinks, they being impossible to create in
    manufacture other than from a badly cut butt joint.

    Jobst Brandt
    [email protected]
     
  9. Chalo

    Chalo Guest

    daveornee <[email protected]> wrote;

    > Ritchey says "* High Tolerance Machined (+0.03mm)" for many of their
    > rims. I have seen similar results in Mavic rims and Velocity rims
    > although I have never see what they specify.


    That's a misleading claim, because they do not specify which
    dimensions are toleranced to that standard. Since they say
    "machined", I assume the .03mm tolerance is on the width between brake
    tracks. That's just over one thousandth of an inch-- serious
    precision but not impossible in a mass-production setting.

    It would be easy enough to hold width and perhaps brake track
    parallelism to such a tolerance. I highly doubt any rim manufacturer
    uses a similarly tight tolerance for flatness, roundness, diameter,
    variation in wall thickness, drilling location, or even squareness at
    the joint.

    Keep in mind that a rim that starts out with a sub-.001" variation in
    width is likely to meet this spec even when worn out and failed
    structurally. It does not imply that the rim will be easy to build
    into a true and durable wheel.

    Chalo Colina
     
  10. dvt

    dvt Guest

    Rob Weinstock:
    >>>Finding an accurate flat will be interesting.


    Andrew Muzi writes:
    >>Lay it on a true wheel. Press it flat before you build it New Rims
    >>arrive within a millimeter


    [email protected] wrote:
    > Pressing a rim against a flat surface will not remove wows that are
    > within the elastic limit of the rim. That means, greater than +-10mm.


    I think Muzi meant to use a true wheel as an indicator, not as a surface
    against which to straighten the rim.

    > ...I don't see that
    > a new rim will have kinks, they being impossible to create in
    > manufacture other than from a badly cut butt joint.


    The OP said this, way back at the beginning of the thread:
    > I recently received a set of NOS rims in the mail. The box had obvious
    > shipping damage.


    I could imagine shipping damage causing kinks...

    I concur with Jobst in that if no kinks are present, 3 mm runout seems
    trivial to correct using spoke tension.

    --
    Dave
    dvt at psu dot edu
     
  11. A Muzi

    A Muzi Guest

    >>>>You can likely bend the rim(s) back flat.

    >>>Finding an accurate flat will be interesting. I have a granite
    >>>inspection stone, but it's only 18" x 12". Garage floors are
    >>>notorious not flat.
    >>>I'm wondering how flat/round rims are from the factory? I mean,
    >>>are there standardized specs that are maintained, etc.?


    > Andrew Muzi writes:
    >>Lay it on a true wheel. Press it flat before you build it New Rims
    >>arrive within a millimeter

    >
    >

    [email protected] wrote:
    > Pressing a rim against a flat surface will not remove wows that are
    > within the elastic limit of the rim. That means, greater than +-10mm.
    > As I said, if the rim is a smooth saddle then forget the wow and build
    > the wheel. That sort of misalignment is trivial to flatten and will
    > not affect performance. Kinks are another matter but I don't see that
    > a new rim will have kinks, they being impossible to create in
    > manufacture other than from a badly cut butt joint.
    >
    > Jobst Brandt
    > [email protected]

    Ahh, the vagaries of English. I was overly terse it seems.

    How to check if a rim is flat? Against another wheel is a
    good quick way to see that.

    I did not intend to imply that one should press a rim
    _against a wheel_ to remove a bend. That's not possible. If
    you inferrred that, it wasn't my intent at all. Across ones
    knee is quicker.

    Commonly when dealing with XMart bikes whose wheels will not
    spin in the bike despite an attempt at truing, we press a
    knee against the rim, bring up some tension and achieve a
    functional wheel in a few minutes. That when even a couple
    of dollars cannot be charged.

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