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I just acquired a yeti arc frame with a BB shell of 73mm. I want to run a middleburn duo crank with two chain rings, with a square taper BB.
What's the ideal BB axle length to get the right chain line?
Thanks for your help!
Hi there.
Middleburn site recommends 113mm for square taper and ISIS BBs.
So you should buy the 73x113 size.
http://www.middleburn.co.uk/tech_faq_cranks.php
This should put the middle of the chainrings (in your case between the pair) in line with the 5th sprocket on a 9-speed.
This may not be ideal if you are always in the lower ring on large sprockets, but is the official 'neutral' fitting.
Note CRC have a cracking deal on the Crank Brothers Cobalt ISIS BB at £25 and it has a 5-year warranty according to the CB and UK Importer's websites.
BB axle length is dictated by the chainset. BB with is obviouslt the chain size. It doesn't matter what frame you're fitting it to..
73 x 113mm is correct.