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  1. #1
    g3h6o3
    Reputation: PissedOffCil's Avatar
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    Offsetting chainrings outwards

    Hello,
    On my new bike build, I was plan inv on running 24-38 chainrings on a triple crankset. I don't have the rings yet but whn installing my triple I wondered if a 38T would clear the frame. After checking with the frame builder it turns out it wouldn't. I need to have a 50mm chainline double for a 38T to clear the frame.

    So I've looked up my options. Given the BB shell is 73mm, I cannot simply move a spa er to the drive side. I think adding a spacer could work but I don't remember seeing anybody do this. I also thought of using offset chainrings but can't find any with a big enough offset to compensate the chainline as required. Does any exist?

    Any other option for me out there?

    Thanks
    Check out my SportTracks plugins for some training aid software.

  2. #2
    mtbr member
    Reputation: Saul Lumikko's Avatar
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    Which cranks and BB are you using? Chances are you could switch to a longer spindle, which would widen your Q-factor a bit, but also move both rings outwards.

  3. #3
    g3h6o3
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    Shimano XT 775 so that is not an option
    Check out my SportTracks plugins for some training aid software.

  4. #4
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    How much do you need? I've been running extra spacers on one of my single speeds for a better chain line without problems. Just can't use the plastic stopper thing on the non-drive side - it won't drop into the hole. The thin spacers for freehubs fit bottom brackets.

  5. #5
    g3h6o3
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    I need around 2.5mm to 3mm, basically a BB spacer.

    The "plastic stopper thingy" you speak of is the hook that prevents the crank from puling out, right?
    Check out my SportTracks plugins for some training aid software.

  6. #6
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    Correct. Without it, if the arm comes loose, it can fall off. I've had no problems running with an extra spacer. Give it a try and see how it looks.

  7. #7
    Bicyclochondriac.
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    Quote Originally Posted by PissedOffCil View Post
    Hello,
    On my new bike build, I was plan inv on running 24-38 chainrings on a triple crankset. I don't have the rings yet but whn installing my triple I wondered if a 38T would clear the frame. After checking with the frame builder it turns out it wouldn't. I need to have a 50mm chainline double for a 38T to clear the frame.

    So I've looked up my options. Given the BB shell is 73mm, I cannot simply move a spa er to the drive side. I think adding a spacer could work but I don't remember seeing anybody do this. I also thought of using offset chainrings but can't find any with a big enough offset to compensate the chainline as required. Does any exist?

    Any other option for me out there?

    Thanks
    If it turns out you can't accommodate the 38t ring easily, have you looked that the difference in gear ratios dropping down to a 36t? It is pretty small difference (about 5%, or half a typical gear change).
    15mm is a second-best solution to a problem that was already solved.

  8. #8
    g3h6o3
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    I've been told a 36 would probably not work either... I really need to keep the 50mm chain line to clear the frame.

    Thx everyone
    Check out my SportTracks plugins for some training aid software.

  9. #9
    Happy Trails
    Reputation: Scott In MD's Avatar
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    Offsetting chainrings outwards

    FSA has a brand new line of rings made specifically to convert 3x9 to 2x10. The are called D-10 rings, and are offset. Also have nifty caps to fill the space on the spline where the big ring used to be. You can find an articles e on BikeRumor or email Chad at FSA for info.

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