Join Date: Apr 2005
Bikes: motobecane mirage/suzue basic flip/glop
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i have just gone through this very thing, and i think i might have a way that may help with a spindle and cups bottom bracket...
if you have a spindle on hand, measure it it like sheldon does on his spindle's page, mount the crank and chainring, and then get the chainring center line. if it is not the 42 that you want, figure out how much you need to change one way or the other. if you can't get the proper chainline with the first setup, you can try flipping the chainring from one side of the crank mounting arms to the other(if it allows) or flipping the spindle(the spindle is usually asymetric). if you still need to get closer to 42, write down all the measurements that you got from the different options provided by your current spindle, figure out how much each option would require to move to get it right and then look for a spindle that has an end that matches this. for example, my original spindle on my motobecane had a drive side that measured 36 mm. i needed to shrink my chainline measurement from 46 to 42, so i found a compatible spindle that had a 32mm side, it wasn't the drive side, but it didn't matter, it was the 4mm i was looking for and i nailed my chainline at a perfect 42. of course all this is useless if you are trying to switch to a cartridge type from the cups and spindle. i considered this and my LBS said they would mount my crank and chainring on a BB, measure it, and pick a cartridge that would either fit or come close(redish would then be necessary).
anyway, i hope i have been a help and not blabbed a bunch of useless info..