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Old 05-06-05, 09:26 AM   #1
genericbikedude
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How does one determine BB spindle length in advance?

Howdy folks,

I'm gettting ready for yet another project bike, and this one is a fixie, so I want to get the chainline just right.

I'll be using a suzue promax with a duraace lockring, giving a chainline of 42 (thank you sheldon). How do I measure a crank to determine what size BB gives a good chainline? I know that new cranks often give recommendation, but I may use a used crank. I'll be usng a square BB, and most likely an old road double crank or one variety or another.

Thanks
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Old 05-06-05, 09:47 AM   #2
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Originally Posted by genericbikedude
Howdy folks,

I'm gettting ready for yet another project bike, and this one is a fixie, so I want to get the chainline just right.

I'll be using a suzue promax with a duraace lockring, giving a chainline of 42 (thank you sheldon). How do I measure a crank to determine what size BB gives a good chainline? I know that new cranks often give recommendation, but I may use a used crank. I'll be usng a square BB, and most likely an old road double crank or one variety or another.

Thanks
Easier to start with a newer crrank and BB with a known chainline as the current 43.5. just grabbing an old double crank involves alot of trial and error with correct spindle length as well as other possible issues. A recent poster was faced with having to dent his chainstays in order to use a preferred crank he had chosen along with the spindle length he wanted for other reasons.
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Old 05-06-05, 09:59 AM   #3
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so there is no good method? just trial and error?
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Old 05-06-05, 11:53 AM   #4
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i've been boggled by this as well. it all depends on what cranks you get. i just settled on some sugino rd's as a fairly cheap option. they take a 107mm bb to get a 44mm line. the mechanic i spoke to said he usually just swaps out spindles till he gets it close.
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Old 05-06-05, 12:55 PM   #5
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Originally Posted by genericbikedude
Howdy folks,

I'm gettting ready for yet another project bike, and this one is a fixie, so I want to get the chainline just right.

I'll be using a suzue promax with a duraace lockring, giving a chainline of 42 (thank you sheldon). How do I measure a crank to determine what size BB gives a good chainline? I know that new cranks often give recommendation, but I may use a used crank. I'll be usng a square BB, and most likely an old road double crank or one variety or another.

Thanks
sheldon also has a BB size database for a bunch of old cranks as well. It's by no means complete, but its fairly comprehensive. full of mostly shimano cranks.
http://www.sheldonbrown.com/bbsize.html
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Old 05-06-05, 02:18 PM   #6
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hi.
i have just gone through this very thing, and i think i might have a way that may help with a spindle and cups bottom bracket...
if you have a spindle on hand, measure it it like sheldon does on his spindle's page, mount the crank and chainring, and then get the chainring center line. if it is not the 42 that you want, figure out how much you need to change one way or the other. if you can't get the proper chainline with the first setup, you can try flipping the chainring from one side of the crank mounting arms to the other(if it allows) or flipping the spindle(the spindle is usually asymetric). if you still need to get closer to 42, write down all the measurements that you got from the different options provided by your current spindle, figure out how much each option would require to move to get it right and then look for a spindle that has an end that matches this. for example, my original spindle on my motobecane had a drive side that measured 36 mm. i needed to shrink my chainline measurement from 46 to 42, so i found a compatible spindle that had a 32mm side, it wasn't the drive side, but it didn't matter, it was the 4mm i was looking for and i nailed my chainline at a perfect 42. of course all this is useless if you are trying to switch to a cartridge type from the cups and spindle. i considered this and my LBS said they would mount my crank and chainring on a BB, measure it, and pick a cartridge that would either fit or come close(redish would then be necessary).

anyway, i hope i have been a help and not blabbed a bunch of useless info..

c.
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