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  1. #1
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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.

  2. #2
    The Left Coast, USA FrenchFit's Avatar
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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.

  3. #3
    coprolite fietsbob's Avatar
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    both external bearing ?

  4. #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.

  5. #5
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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.

  6. #6
    Low car diet JiveTurkey's Avatar
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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.
    Quote Originally Posted by slopvehicle View Post
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  7. #7
    Bianchi Goddess Bianchigirll's Avatar
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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
    Bianchis '87 Sport SX, '90 Proto (2), '91 Boarala 'cross, '93 Project 3, '88 Trofeo SOLd, '86 Volpe, '89 Axis SOLD, '79 Mixte SOLD, '99 Mega Pro XL Ti SOLD, '97 Ti Megatube, , '90 something Vento 603,

    Others but still loved,; '80 RIGI, '80 Batavus Professional, '87 Cornelo, '86 Bertoni (sold), '09 Motobecane SS, '98 Hetchins M.O., '09 K2 Mainframe SOLD, '89 Trek 2000, '?? Jane Doe (still on the drawing board), '90ish Haro Escape

  8. #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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