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  1. #1
    如果你能讀了這個你講中文 genericbikedude's Avatar
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    How wide are Mavic MA40's?

    I know that hard anodizing sucks and all, but they are cheap. How wide are they??

  2. #2
    sch
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    A google on the rim brings up a table suggesting 20.3mm wide.
    Steve

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    Senior Member DannoXYZ's Avatar
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    Why does hard-anodizing suck? It's a surface that's 10x stronger and longer-lasting than bare aluminium..

  4. #4
    cs1
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    Quote Originally Posted by DannoXYZ
    Why does hard-anodizing suck? It's a surface that's 10x stronger and longer-lasting than bare aluminium..
    Not really. It's more decorative than usefull. It is also prone to being very brittle. It can crack and wind up doing more harm than good. There might be an article on Sheldon Brown's site concerning anodizing. I know there is one floating around cyber space somewhere. If it really was so good, why do most manufacturers machine it off of the braking surface? Isn't that where you want a hard protective surface?


    Tim
    1999 Waterford RSE-11, 1995 Waterford 1200, 1989 Specialized Rockhopper Comp
    1989 Raleigh Technium, 1989 Schwinn Traveler, 1986 Specialized Rockhopper
    1984 Specialized Stumpjumper, 1986 Specialized Stumpjumper and just way too many projects to list.

  5. #5
    Pedalpower clayface's Avatar
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    Quote Originally Posted by cs1
    I know there is one floating around cyber space somewhere.
    Jobst Brandt, wheel guru, wrote this about anodized wheels:

    "Dark anodized rims were introduced a few years ago as a fashionable
    alternative to shiny metal finish, possibly as a response to non
    metallic composites. Some of these rims were touted as HARD anodized
    implying greater strength. Hard anodizing of aluminum, in contrast to
    cosmetic anodizing, produces a porous ceramic oxide that forms in the
    surface of the metal, as much as 1/1000 inch thick, about half below
    the original surface and half above. It is not thick enough to affect
    the strength of the rim but because it is so rigid, acts like a thin
    coat of paint on a rubber band. The paint will crack as the rubber
    stretches before any load is carried by the rubber. Similarly,
    anodizing cracks before the aluminum carries any significant load.

    Rims are made from long straight extrusions that are rolled into
    helical hoops from which they are cut to length. Rims are often
    drilled and anodized before being rolled into a hoop and therefore,
    the anodizing is already crazed when the rim is made. Micro-cracks in
    thick (hard) anodizing can propagate into the metal as a wheel is
    loaded with every revolution to cause whole sections of the rim to
    break out at its spoke sockets. In some rims, whole sidewalls have
    separated through the hollow chamber so that the spokes remained
    attached to the inner hoop and the tire on the outer one. In
    contrast, colored anodizing is generally too thin to initiate cracks.

    As an example, Mavic MA-2 rims have rarely cracked except on tandems,
    while the identical MA-40 rims, with a relativley thin anodizing, have
    cracked often.

    Anodizing is also a thermal and electrical insulator. Because heat is
    generated in the brake pads and not the rim, braking energy must flow
    into the rim to be dissipated to the atmosphere. Anodizing, although
    relatively thin, impedes this heat transfer and reduces braking
    efficiency by raising the surface temperature of the brakes. When
    braking in wet conditions, road grit wears off anodizing on the
    sidewall, an effect that improves braking.

    Anodizing is not heat treatment and has no effect on the structural
    properties of the aluminum."

    The link: http://draco.acs.uci.edu/rbfaq/FAQ/8c.2.html


    Roberto

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