Cycling Equipment · Public discussion

Spindle (or BB) offsets?

Started by !Jones · · Last activity · 2 posts · 324 views

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Cycling Equipment
Published
12 January 2005
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12 January 2005
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!Jones
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  1. On a Phil Wood bottom bracket, where is the "offset" controlled? Is
    this a function of the spindle? If so, then why isn't that datum
    required when ordering just a spindle alone? For example: according to
    my super computer, optimally, I need a 122mm spindle with an 8mm right
    offset or as close as I can get to that in the real world. I
    understand that I can get +-5mm by adjusting the cups L/R. BB
    cartridges sold without cups tend to specify an offset such as "R+5".
    That the spindle alone doesn't have an offset specified but the BB
    cartridge does leads me to believe that this value is controlled to
    some extent by the BB assembly independently of the spindle and
    position of the cups. Am I correct in this belief?

    This old tandem is definitely a "weird load". It looks like someone
    once set up a way to shift the timing chain on one end between a 32 and
    34 tooth timing ring. I am assuming that the logic here was to change
    the crank synchronization dynamically... shift, pedal until you reach
    the desired synchronization, then shift back (that adds about 3 lbs of
    hardware!) It's an interesting idea; however, I believe that I'm going
    to have to cite Murphy's Law, scrap it, and return to the stock
    configuration. Simplicity has its own beauty, IMO.

    Jones, who seeks only wisdom, enlightenment, and to serve God... and to
    grow rich, of course, as all men.

  2. A shy person said:

    On a Phil Wood bottom bracket, where is the "offset" controlled? Is
    this a function of the spindle? If so, then why isn't that datum
    required when ordering just a spindle alone? For example: according to
    my super computer, optimally, I need a 122mm spindle with an 8mm right
    offset or as close as I can get to that in the real world. I
    understand that I can get +-5mm by adjusting the cups L/R. BB
    cartridges sold without cups tend to specify an offset such as "R+5".
    That the spindle alone doesn't have an offset specified but the BB
    cartridge does leads me to believe that this value is controlled to
    some extent by the BB assembly independently of the spindle and
    position of the cups. Am I correct in this belief?

    Yes. You can install the spindle with any desired offset, there are no
    shoulders to locate it, it's all done with Loctite.

    Quoted message said:


    This old tandem is definitely a "weird load". It looks like someone
    once set up a way to shift the timing chain on one end between a 32 and
    34 tooth timing ring. I am assuming that the logic here was to change
    the crank synchronization dynamically... shift, pedal until you reach
    the desired synchronization, then shift back (that adds about 3 lbs of
    hardware!)

    I doubt that's it. Most likely the extra chainring was for use with a
    stokid kit, a bottom bracket that clamps onto the rear seat tube so that
    a small child can reach the pedals.

    There's a not too good picture at:

    http://sheldonbrown.com/harris/tandem.html#stokid

    Sheldon "My Stokids Are All Grown Up" Brown
    +------------------------------------------------------+
    | I'm not a member of any organized political party, |
    | I'm a Democrat! -- Will Rogers (1879-1935) |
    +------------------------------------------------------+
    Harris Cyclery, West Newton, Massachusetts
    Phone 617-244-9772 FAX 617-244-1041
    http://harriscyclery.com
    Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com

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