scubagirl
03-22-02, 06:36 AM
How do you find out what size to get? There are 3 or 4 to choose from.
Bicycle Mechanics - Bottom Bracket size?
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John E
03-22-02, 07:35 AM
Relevant parameters:
1) Bearing cup diameters and threads -- most newer bikes use English/ISO, although some Italian makers stubbornly cling to their traditional standard. Pre-1985 French, German, Austrian, and Swiss bikes use much harder-to-find purely metric cups (sheldonbrown.com).
2) BB shell width: 68mm on most bikes, 70mm for Italian road bikes, or 73mm for most oversized aluminum frames. You can easily measure this parameter yourself.
3) Number of chainrings, which affects the spindle length.
4) Brand of crank, which affects the spindle taper.
5) With newer cranks and BBs, the type of crank-to-spindle connection, i.e., traditional square-taper vs. splined.
If in doubt, buy from a competent local bike shop, and bring in your frame and cranks to help them size up your requirements.
1) Bearing cup diameters and threads -- most newer bikes use English/ISO, although some Italian makers stubbornly cling to their traditional standard. Pre-1985 French, German, Austrian, and Swiss bikes use much harder-to-find purely metric cups (sheldonbrown.com).
2) BB shell width: 68mm on most bikes, 70mm for Italian road bikes, or 73mm for most oversized aluminum frames. You can easily measure this parameter yourself.
3) Number of chainrings, which affects the spindle length.
4) Brand of crank, which affects the spindle taper.
5) With newer cranks and BBs, the type of crank-to-spindle connection, i.e., traditional square-taper vs. splined.
If in doubt, buy from a competent local bike shop, and bring in your frame and cranks to help them size up your requirements.
Richard D
03-22-02, 09:32 AM
Vaguely on topic...
Can a UN72 be used as a direct replacement for a UN52, or are there differences besides weight?
Thanks
Richard
Can a UN72 be used as a direct replacement for a UN52, or are there differences besides weight?
Thanks
Richard
scubagirl
03-22-02, 09:39 AM
He is looking @ BB-ES70 there are 4 sizes. I could have been more specific before. It's a Trek Y-bike either med or large frame. Could I go to a website or something to get some specs on it?
ljbike
03-22-02, 10:49 AM
Measure the length of the spindle; It will range from 107mm to over 120. Then measure the BB shell: most are 68; some 70 and 72. Take those 2 dimensions to a bike shop and they'll give you the right BB. You also need to tell them if it's for a double or triple chainring and the brand of cranks.
ljbike
03-22-02, 10:50 AM
Richard, it shouldn't be a problem.
--walt--
03-23-02, 06:45 PM
68-113
John E
03-23-02, 07:44 PM
Originally posted by Richard D
Can a UN72 be used as a direct replacement for a UN52, or are there differences besides weight?
I have yet to find a pair of cranks (including Shimano's own RSX!) that will seat fully (and what I consider properly) onto a UN-72. Therefore, the UN-72 I bought for son #1's bike (68mm BB shell width) turned out to be about right for son #2's bike (73mm BB shell width). The spindle of the UN-72 I finally used for son #1's bike is 5mm shorter than the one it replaces.
I had always heard that Shimano uses the same taper, but a larger ultimate diameter, than Campagnolo, but I really would have expected a Shimano crankset to seat properly onto a UN-72 BB!
Can a UN72 be used as a direct replacement for a UN52, or are there differences besides weight?
I have yet to find a pair of cranks (including Shimano's own RSX!) that will seat fully (and what I consider properly) onto a UN-72. Therefore, the UN-72 I bought for son #1's bike (68mm BB shell width) turned out to be about right for son #2's bike (73mm BB shell width). The spindle of the UN-72 I finally used for son #1's bike is 5mm shorter than the one it replaces.
I had always heard that Shimano uses the same taper, but a larger ultimate diameter, than Campagnolo, but I really would have expected a Shimano crankset to seat properly onto a UN-72 BB!
--walt--
03-24-02, 06:37 PM
Scubagirl
I major league screwed up and I am Sorry!!!!
The Y bike is a 73mm shell, still with a 47.5 chainline requiring a 113 spindle for Shimano XT, LX or Deore cranks.
I hope I didn't cause any problems.
I major league screwed up and I am Sorry!!!!
The Y bike is a 73mm shell, still with a 47.5 chainline requiring a 113 spindle for Shimano XT, LX or Deore cranks.
I hope I didn't cause any problems.