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I'm after a new chainset and up to now have always used square taper.
So how do these external type chainsets work? How do I know if it will fit - I see that they fit 68 or 73mm bb shells but what about axle length (currently 113mm sq.taper) to get the chainline correct?
There is only one axle length available.
Axle is fixed to one of the arms (drive on Shimano, non-drive on Raceface.
Fit bottom bracket with correct spacers to suit shell width, slide axle through and pop other arm on. Preload, do up pinch bolts and your sorted.
Its an easy system, just read the instructions and you'll be fine.
I see. So if spacers are used to move the drive side crank out a bit then the non-drive side one comes in and the cranks are off-centre, is that right?
Only three spacers on the Shimano system- all 2.5mm thick, all sit on the bottom bracket (between the cup and frame)
68mm shell uses three (two on the drive side, one on the non-drive.
73mm shell uses one- on the drive side.
So the cranks sit 2.5mm further to one side, but its not an issue.