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  1. #1
    Join Date
    Jul 2010

    Talk to me about Bottom Brackets?

    Normally I am quite able to service my bike on my own but this is totally new for me:

    I'd like to switch the cranks and bottom bracket on my going-to-town-bike. My plan is to go from a double to a single chainring, 'cause I just don't use the smaller one at all. Currently, there is a "Truvativ"-System bottom bracket installed (the kind normally used on a mountain bike).
    So, as the bike is a Soma-mixte, I'd like to switch to a more old-school look for the cranks (something like those http://www.befixed.de/Kurbeln/Track-...-Set::778.html) - and for those, when I got it right, I would have to switch the bottom bracket too. I figured out that I should use a "JIS" bottom bracket, 113 mm long.

    When I look for JIS-bottom brackets, there are two standards: "BSA" and "ITA" (which stands for british and italian?). The threading on those two are different.

    Ok... how do I find out which one I should get? I would have thought that something like that should be easy to find out by looking at the bike manufacturers site, but... not really... it says:
    "Bottom bracket: 68mm"

    Is it true that this means its JIS ITA (read this as a side note on another discussion regarding bottom brackets...)?
    Is there a way to find out by looking at my bike?

    I feel like there is a secret conspiracy to prevent ordinary people from finding out the dirty secrets about bottom bracket standards why is this soooo complicated?

  2. #2
    Join Date
    Dec 2010
    Boise Idaho
    Read this blog post by Jan Heine BB Demystified Think it will be helpful.
    Sky King
    Gilles Berthoud "Bernard"
    Surly ECR "Eazi"
    Empowering the Bicycle Traveler

  3. #3
    Join Date
    Jul 2010
    Thank you a lot. Sky King, wow, that was really helpful, I knew it wouldn't be that complicated when explained right
    Sheldon Brown provides a lot of information too but I just could't get to the bottom of what he was trying to tell me

    So I'm pretty sure the Soma uses the british standard, but I can just check the threading once I remove the old BB.

  4. #4
    Join Date
    Jun 2012
    I'm pretty sure Sheldon Brown will provide answers, have a look at his website



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