[jeepguy812]

Hi ,i'm switching from a square taper BB/suntour xc crank to a octalinkBB/shimano fc-m571 crank setup. My old BB says BB-cs21 73 bc1.37x24 and is 122-123mm from end to end.With the old setup i had around 5mm clearance from crank arm to stay.

What size octalink BB do i need to get the same fit with the 571's?

Thanks and sorry if this is a dumb question.

 

[Bikinfoolferlife]

Your old crankset used a bb appropriate to it and your bb shell (a 73mm width). You need to buy the appropriate Shimano V2 splined bb specific to your new cranks for a 73mm shell, either a 113 or 118 spindle length depending on the chainline you want, probably the 113 would be fine for a nominal 47.5mm chainline. Start here www.sheldonbrown.com/bbsize.html and also read Sheldon's article on chainline linked on that page.