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  1. #1
    Commuting Fool
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    Help my fixie get a 42mm chainline!

    Or whatever ideal is with 120mm rear hub spacing

    Right now, I use a 68x103mm and when the chainring is on the inside, the cl is 38/39mm. When I stick the ring on the outside of the crankset, it is about 45mm.

    Do I need to go to a 107mm or 110mm to get the chainline to the 42mm I'm looking for (chainring on inside I assume is the only way)?
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    When you lose yours, it's a depression" - Harry S Truman

  2. #2
    cab horn
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    Assuming your crank is JIS and ignoring chainring/spider frame clearance issues then if you can obtain a ISO bb, say Phil (or any ISO bb) 68x104.5 will set your crank up with the ring on the outside with 42mm chainline.

    If you want a cheaper option then, run the ring on the inside and get a 68x107 bb for a 42/43mm chainline.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  3. #3
    Commuting Fool
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    Quote Originally Posted by operator View Post
    Assuming your crank is JIS and ignoring chainring/spider frame clearance issues then if you can obtain a ISO bb, say Phil (or any ISO bb) 68x104.5 will set your crank up with the ring on the outside with 42mm chainline.

    If you want a cheaper option then, run the ring on the inside and get a 68x107 bb for a 42/43mm chainline.
    It's a generic JIS crankset as I recall. How is the ISO bb different? From what you describe, the pedals arms seat more deeply onto an ISO spindle??
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    "When your neighbor loses his job, it's a recession.
    When you lose yours, it's a depression" - Harry S Truman

  4. #4
    Senior Member
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    Quote Originally Posted by Autobus View Post
    Or whatever ideal is with 120mm rear hub spacing

    Right now, I use a 68x103mm and when the chainring is on the inside, the cl is 38/39mm. When I stick the ring on the outside of the crankset, it is about 45mm.

    Do I need to go to a 107mm or 110mm to get the chainline to the 42mm I'm looking for (chainring on inside I assume is the only way)?
    Chainrings on a normal road double crank are spaced 5mm apart. So if you think you might have had a 38mm chainline on the inside position, you will have a 43 on the outside. Close enough to 42. Might want to measure again to see if it is really 38/43 or 39/44.

    Also, yes a JIS crank will slide farther inboard on the same length ISO spindle.

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