Zula Posted November 11, 2009 Share Heres one for the techies, If I want to replace a crank, do I need to replace the BB as well? Or is a crank compatible with all BB's? If not, how do I know if a particular BB will fit my frame? So for example are there several different BB's which one could use for a shimano 105 crank? Thanks!! Link to comment Share on other sites More sharing options...
Tankman Posted November 11, 2009 Share there are many different types of bb's octalink ISIS Square Taper External etc. these can have english 68mm or italian 70mm threading your crank will determine what bb to use and the frame will determine if it should be english or italian (easily done by measuring the length of the bb on the frame) not to sure what 105 cranks normally use, but on fsa cranks there is normally an inscription what type of crank it is... Link to comment Share on other sites More sharing options...
Tankman Posted November 11, 2009 Share oh if your crank has an axle attached to the drive side, you will use an external bb, sometimes called bb cups. Link to comment Share on other sites More sharing options...
mountain_lion Posted November 11, 2009 Share You asked a general question, so here is a general answer... There are various types of BBs and a crank set is normally designed to be used with only one type of BB. The BB thread in the frame is most likely British, but could also be Italian. Shell width also differs between frames. So if you want to keep the same BB, you are limited to compatible crank sets. If you decide to replace the BB as well, the options become wider, i.e. you can fit a different type of BB in order to change to a different design crank set, as long as you get a BB which is compatible with your frame. Link to comment Share on other sites More sharing options...
Tankman Posted November 11, 2009 Share octalink shimano 105 bb Link to comment Share on other sites More sharing options...
Tankman Posted November 11, 2009 Share external bb Link to comment Share on other sites More sharing options...
techguy Posted November 12, 2009 Share Assuming you have the newer 105, which will use the external (Hollowtech 2, Shimano TM) BB then you can fit any Hollowtech 2 crankset to that. The old 105 system with the Octalink BB is generally a 109mm length and that will fit most frames, excluding the italian BB frames, of which there seem to be fewer and fewer these days as most manufacturers are going to the english thread... Link to comment Share on other sites More sharing options...
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