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Old 05-13-07, 03:48 AM   #1
Collie
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a quick BB question

hi,

so according to sheldon brown:

the sugino xd600 crankset needs a square bb 113-118mm

i have a 110mm bb on the thorn sherpa so i get a little rubbing when in the lowest gear combo. i'm not sure if this is simply an annoyance or if it can cause significant damage to other components??? (please comment!)

so looking at sjscycles.co.uk there are a selection of 68mm bb's that seems to be suitable, but what is the difference between them: un51/52/53; un72/3; un54?????
any ideas?

also what length is advisable? the shortest possible? i.e. 113mm. or is there any benefit to a longer spindle? 115-118mm??
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Old 05-13-07, 07:39 AM   #2
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What kind of rubbing are you getting. Is it a chainring on the frame or is it the front derailer rubbing on the chain. From the specs you provide it would appear that you need either a 113mm or 118 mm BB to have a good chainline. It also might be useful to measure the chainline. Lenard Zinn's Zinn and the Art of books have a good discusion on this.
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Old 05-13-07, 06:35 PM   #3
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I use 115mm with that crankset, seems to work well.
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Old 05-13-07, 09:35 PM   #4
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You seem to have run into the downside of the wrong BB, You can get a decent one for a rather small price. The trouble is finding which one you need. You can go by standard texts, and if you can't find what you want at that point you may have to build a few options. You should be able to tell how much you are off, and then nail it on your second try. With everything mounted on your 112, can't you use a ruler or a piece of string to figure out where you need to go next?
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Old 05-17-07, 07:16 AM   #5
slabfoot
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My LBS has a box of old bottom brackets. It really takes the guesswork out of buying the new one if you have tried one or two on first.
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Old 05-17-07, 07:38 AM   #6
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Quote:
Originally Posted by Collie
hi,

so according to sheldon brown:

the sugino xd600 crankset needs a square bb 113-118mm

i have a 110mm bb on the thorn sherpa so i get a little rubbing when in the lowest gear combo. i'm not sure if this is simply an annoyance or if it can cause significant damage to other components??? (please comment!)

so looking at sjscycles.co.uk there are a selection of 68mm bb's that seems to be suitable, but what is the difference between them: un51/52/53; un72/3; un54?????
any ideas?

also what length is advisable? the shortest possible? i.e. 113mm. or is there any benefit to a longer spindle? 115-118mm??

Get a BB you can easily adjust left to right, the Phil Wood's are expensive, but give you a couple of mm of easy
adjustment to get your chain line right. The BB length required will be dertemined by the crank, the spacing of the
chainstays and the size of your smallest ring. I have a bike with 135 mm rear separation and I find that a 111mm BB works
well with the Sugino XD.I run it as a double with a 26t small ring and have to offset the BB 2mm to the right to get chainstay/ring
clearance and chainline right.

Why not call Thorn and ask them

Last edited by nun; 05-17-07 at 07:48 AM.
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