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Bottom Bracket Sizing - the second number?(6 posts)

Bottom Bracket Sizing - the second number?jose_Tex_mex
Jun 10, 2002 2:29 PM
All,
Thanks for any help.
Say you have determined that your BB is 68 mm English. Now you want to order and need to determine the second number: 103, 105, and so forth. What exactly does this number mean and how do you know which one you need. I believe it goes to chainline.
Thanks
Half and answerczardonic
Jun 10, 2002 2:43 PM
It is the width of the spindle/axel. If you are replacing an old BB, measure the spindle from end to end to get the correct size.
You're right.the dad
Jun 10, 2002 2:43 PM
Actually, it refers to the spindle length. As a general rule, if you buy a new crank, the crank will recommend a spindle length that works for MOST bike frames. If you are just replacing the bottom bracket and keeping the same crank, simply measure the spindle you are replacing.
New Frame - Old Bottom Bracketjose_Tex_mex
Jun 10, 2002 5:03 PM
All,
Thanks for the previous responses.
As it stands I am getting a new frame. Thus I do not have a spindle to measure. One other complication is that I am using old cranks. They haven't been overtigtened. However, I expect they will slide on a bit further than normal.
Therefore, without the knowledge of original spindle and given used cranks, how would one make the spindle length call?
Some BB are adjustable for chain linePaul
Jun 11, 2002 3:38 AM
What brand cranks do you have? Are you replacing other components? Nine speed or eight speed? If you are just replacing the BB, and keeping everything else, I would look for an adjustable BB so that you can get correct chainline.
Personnally, get a new drive train for you new frame. You could just be getting deeper into problems, and it's not really worth it.
Contact the manufacturer.czardonic
Jun 11, 2002 9:32 AM
The documentation that comes with cranksets usually gives you a BB width spec. You might be able to track it down on the web, or call the manufacturer.

Also, someone else who uses the same crank is probably using the same BB size.