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Old 05-10-11, 07:52 AM   #1
5shot
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Replace BB when switching cranksets?

My road bike has a full Dura Ace 7900 drivetrain. The crankset has 53/39 rings. I will be participating in some heavy duty climbing in Colorado in a couple of months and have been considering temporarily replacing the crankset with a compact crankset while I am in the mountains.

My question is... if I swap out the current 7900 crankset for a 7950 (Dura Ace compact) will I need to replace the BB as well? If the answer is 'yes' then when I swap back to the 7900 crankset, should I replace the BB with the original one?

Thanks.
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Old 05-10-11, 08:24 AM   #2
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I don't know the specs. of the cranks you are referring to and whether there is a clearance or spindle issue, but if this is a preference question: I don't switch BBs unless there is a compelling reason.
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Old 05-10-11, 08:28 AM   #3
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both external bearing ?
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Old 05-10-11, 08:30 AM   #4
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Both cranks use the same spec HT2 BB, can't see any point in replacing the BB unless it has an issue, say with the bearings.
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Old 05-10-11, 08:52 AM   #5
5shot
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jimc101 is correct. Both cranksets use the same BB. In fact, the cranksets are virtually identical. The only difference is that the standard crankset has a 130BCD and thus larger diameter rings while the compact crankset has a 110 BCD and smaller diameter rings.

I was pretty sure that I didn't have to change BBs but I remembered reading somewhere that the BB should be changed whenever cranksets were changed.

Thanks for the input.
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Old 05-10-11, 09:34 AM   #6
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Quote:
Originally Posted by 5shot View Post
I was pretty sure that I didn't have to change BBs but I remembered reading somewhere that the BB should be changed whenever cranksets were changed.
Only if getting a different crank that requires a bottom bracket with new standard or dimensions. With cartridge bearing BBs, you run 'em till they start acting up. If it ain't broke, don't fix it.
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Old 05-10-11, 11:39 AM   #7
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what kind of frame do you have? you may need to adjust the FD lower and a brazeon type may be too high
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Old 05-10-11, 11:53 AM   #8
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Bianchigirll,

The bike is a 2010 Cervelo R3. Thus, it has a tab for a braze on front derailleur. I know that I will need to lower the derailleur and it looks as though there is still enough room on the hole in the tab to make the needed adjustment. Also, I will be adding a Rotor chain keeper to prevent the chain from coming off when it drops from the large to small chainring.
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