3

Replaced Shimano Bottom Bracket, now front derailleur won't shift to largest gear

How do I measure a bottom bracket?

I thought the only thing that mattered when replacing a bottom bracket was the thread size (68mm) and the spindle length. - unsavory

Me too. I had thought that the things to consider are:

  • Thread specification e.g BC 1.37 x 24, English or Italian
  • Thread width: 68 or 73mm
  • Cranks interface
  • Spindle length e.g. 113mm

And now it turns out the axis offset matters. How do I determine this before purchase. E.g. in this datasheet there is no mention if the axis is symmetrical or offset.

When should I be worried about unsymmetrical BB spindles and where should I check to ensure compatibility?

Improve this question
3
  • Adjusting the derailleur won't work?
    – Alexander
    Commented Oct 16, 2013 at 20:05
  • @Alexander, I mean before purchase. How do they denote non-symmetric BBs? A couple of examples in datasheets, for example.
    – Vorac
    Commented Oct 17, 2013 at 10:29
  • Sorry, my English is pretty bad (so maybe I didn't understand what you wrote), but when you choosing a BB, you have to look also at the length of pin that in chain side (if you want to avoid adjusting derailleur). "113mm" as you wrote is the full length of BB.
    – Alexander
    Commented Oct 31, 2013 at 21:59

1 Answer 1

Reset to default
1

With Shimano there are "E" and "K" variations of bottom brackets that refer to coaxial mounted front derailleurs and chain guards respectively. The BB variations provide for enough space on the drive side spindle to build in another "ring" of the derailleur or the chainguard carrier.

For exact paramenters Sheldon Brown could be helpful too. http://sheldonbrown.com/bbdrop.html

Improve this answer
1
  • 1
    I'm vaguely recalling that a Phil Wood site lists some BBs and their dimensions.
    – Daniel R Hicks
    Commented Nov 18, 2013 at 23:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.