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  1. #1
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    Chainline and GXP BB on older frame

    I have a 2008 Kona Cinder Cone that I recently converted to 2x10 using Truvativ AKA 2.1 crankset with the GXP BB and Deore XT groupset. When I take a careful look, it seems that the chainline on the 36t ring isn't centered on the center of the cassette. So when I shift to the big ring and 36T rear cog, the line isn't straight and it rub the front derailleur. It sometime force the rear derailleur to jump down one cog.

    It just dawned that it might be possible that the frame was not made for a external BB in mind so it's a bit shifted toward the drive side ? How about more recent frames which were designed with external BB in mind ?

    I planned to buy a carbon 29er frame during the winter and move the components over but for now, I need to make sure the drivetrain is working as expected and to avoid early wear.

  2. #2
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    You shouldn't be using the big front and big rear at the same time. Cross chaining.
    Having said that, older cranksets usually had a chainline around 47mm. New ones are around 50.
    If you have enough clearance for the granny and chainrings at the chain stay, you can move one of the spacers on the BB from the driveside to the other side to improve the chainline.

    Forgot it was GXP - although if the bottom bracket is 68mm it should still work.

  3. #3
    Nouveau Retrogrouch SuperModerator
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    Chainline and GXP BB on older frame

    Quote Originally Posted by Xilikon View Post
    I have a 2008 Kona Cinder Cone that I recently converted to 2x10 using Truvativ AKA 2.1 crankset with the GXP BB and Deore XT groupset. When I take a careful look, it seems that the chainline on the 36t ring isn't centered on the center of the cassette. So when I shift to the big ring and 36T rear cog, the line isn't straight and it rub the front derailleur. It sometime force the rear derailleur to jump down one cog.

    It just dawned that it might be possible that the frame was not made for a external BB in mind so it's a bit shifted toward the drive side ? How about more recent frames which were designed with external BB in mind ?

    I planned to buy a carbon 29er frame during the winter and move the components over but for now, I need to make sure the drivetrain is working as expected and to avoid early wear.
    New frames have the same issues.

    No current mtb crankset has a proper chainline. They have all been moved WAY too far outboard to create clearance for short stays, big tires and the front derailleur and chainrings.
    The now standard crank chainline would work better with a 150mm rear hub spacing rather than 135/142.
    mtbtires.com
    The trouble with common sense is it is no longer common

  4. #4
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    Mine has a 73mm BB shell so there is no spacers, otherwise i would have tried that.

    Thanks for the answer shiggy, that's what I'm afraid to know. However, it's no biggie since I know it's not really supposed to shift to big-big but with a 2x10 crank, I expected a better chainline. I find this to be a bad oversight of manufacturers to not agree with a set chainline offset amount and chainline.

    Just having the line with big chainring and the next biggest cog works perfectly with zero rub.

  5. #5
    Nouveau Retrogrouch SuperModerator
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    Chainline and GXP BB on older frame

    Quote Originally Posted by Xilikon View Post
    Mine has a 73mm BB shell so there is no spacers, otherwise i would have tried that.

    Thanks for the answer shiggy, that's what I'm afraid to know. However, it's no biggie since I know it's not really supposed to shift to big-big but with a 2x10 crank, I expected a better chainline. I find this to be a bad oversight of manufacturers to not agree with a set chainline offset amount and chainline.

    Just having the line with big chainring and the next biggest cog works perfectly with zero rub.
    Mostly the manufacturers HAVE agreed on crankset chainlines. It is what you have and too wide. Using a current triple crank with the outer ring removed gives a better chainline than the double-only cranks.
    mtbtires.com
    The trouble with common sense is it is no longer common

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