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  1. #1
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    Being cautious...crankset-bottom bracket compatibility question.

    I'm turning my 80's road bike into a singlespeed (mostly for maintenance benefits and discomfort of downtube shifters). I have a new crankset, but need to get a bottom bracket. The problem I've had with bottom brackets is that the bike frame is an Italian thread, and my options for square-tapered bottom brackets is extremely limited.

    The real question:

    The crankset specs say it accepts 108mm bottom brackets. The closest bottom brackets available are 107 and 110. Which one is the way to go? Neither?

    Thanks.

  2. #2
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    if the 108 spindle gives you the ideal chainline then i would get the 107

  3. #3
    Senior Member Mr. Fly's Avatar
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    Quote Originally Posted by nepg View Post
    The problem I've had with bottom brackets is that the bike frame is an Italian thread, and my options for square-tapered bottom brackets is extremely limited.
    ...

    The crankset specs say it accepts 108mm bottom brackets. The closest bottom brackets available are 107 and 110. Which one is the way to go?
    BB spindle lengths are specified by the factory with a particular chainline in mind. That also means it is matched to the intended use of the crank. To answer your question, you need to clarify if you're converting a double to a single because that may mean you need to adjust from the factory spec to get that one chainring lined up. If your new crank is designed as a single, then I would go with 107mm, assuming acceptable clearance, because your chainline is then off by only 0.5mm. Using the 110mm spindle will throw off the chainline by 1.5mm (half of 3mm).

    In addition to the spindle length and BB threading, do you know if you also have the correct spindle taper? There's JIS and ISO and although they may be cross-compatible (to some extent), using one for the other will definitely impact your chainline.

  4. #4
    coprolite fietsbob's Avatar
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    I have a new crankset, but need to get a bottom bracket.
    +1 , ... so is it a track/single speed crank?

    using 1 out of a double , the chain line runs thru the spider arm. so both chainrings are off that line .

    but no clue what real chaineline you got.. lay a yardstick on the cog and see.

  5. #5
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    Yup, it's a singlespeed crank.

  6. #6
    Old fart JohnDThompson's Avatar
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    Go with the 107 spindle.

  7. #7
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    TO make you feel good... from 108 to 110 are 2 mm difference... 1 mm per side. Doubt that will be a problem or noticeable in the chain line specially using road crankset and track chains.

    from 108 to 107 u have 1/2 mm per side, thats nothing.

    In numbers looks like too much difference between 108 and 110 but is just nothing, probably a 112 will work fine also (2 mm per side)

    Good luck.

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