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@JacqueLucque
I have a perplexing chainline question.
I intend to ‘build’ a new 2x11 drivetrain for our tandem based around Shimano Cues components.
Unsurprisingly, Shimano does not produce a Cues tandem crankset. As such, I will use generic to-be-determined 11-speed chainrings mounted to our existing Deore XT M730-T crankset(s). This is a triple crankset.
The chainline of an XT-M730-T crankset is as follows:
122.5mm BB = 47.5mm chainline
127.5mm BB = 50mm chainline
Those figures, of course, assume the middle-chainring as the centre of your chainline.
Converting the crankset to 2x, I will either mount the chainrings to the middle and outer, or middle and inner. This which will result in a different ‘effective’ chainline’.
The chainline for a Cues 2x crankset is 48.8mm.
Making matters more complex, our tandem has a 145mm-spaced rear end. The wheel is built around this hub. The bike does, at least, use a standard 68mm shell.
In summary, what combination of chainring positions and BB spindle lengths will result in a chainline (or effective chainline) closest to 48.8mm?
Further considerations: I intend to spec an 11-45t cassette. If I use the middle chainring position (110mm BCD) for the ‘inner’ I will be limited to a minimum 33t chainring, giving me a 20in low gear.
That’s approx 2in higher than our current 24x36t 9-speed setup. It would be preferable if I were able to use the inner chainring mount so I can spec smaller chainrings. The position of the inner chainring is also determined by removable spacers, providing chainring spacing adjustability.
Apologies if that’s as clear as mud! Happy to elaborate further if required.