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  1. #1
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    Will a narrower BB/Spindle cause less frame flex?

    I have a Caad12 fitted with a BB Infinite, BB30-to-GXP, conversion kit. It has some bottom bracket flex like all bikes do. I知 just wondering if I were to install a BB30 crank, will it have less bottom bracket flex. My thinking is that the narrower position of the bearings, and shorter spindle will exert less torque on the bottom bracket, than the outboard bearings and longer spindle of GXP. The engineers also designed the entire frame around BB30. Thanks.

  2. #2
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    I can't imagine it would result in a tangible difference because I'd expect the crankarms would wind up in the same position so your applied force positions would remain.

    All these oversized BB designs are such that the benefits of each are not different enough to hold a debate over.

    What is your end goal with this question; are you trying to achieve something or having a problem that you're trying to address?

  3. #3
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    When I sprint out of the saddle, and I知 in the fastest gear combo, I can hear the front derailleur rubbing against the chain. Kinda annoying. It would cost me about $100 to change over. Plus I could change to 175 mm cranks, which I知 more comfortable with.

  4. #4
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    I suggest check/adjust the clearance of the FD first if you have not already done so. A tweak of the limit screw may resolve your rubbing issue.

  5. #5
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    Your crank is flexing, not the BB axle. The BB area, including the large diameter axle, is too stiff to allow that much flex. If you truly think a change in bearing location would address the issue, you'd want the bearings CLOSER to the crankarms, not more centerline to the frame.

    You could go down a real expensive rabbit hole trying to find a stiffer crank, and your desire to go to a longer crankarm albeit a miniscule 2.5mm, will only exacerbate the issue.

  6. #6
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    Quote Originally Posted by SFTifoso View Post
    When I sprint out of the saddle, and I知 in the fastest gear combo, I can hear the front derailleur rubbing against the chain. Kinda annoying. It would cost me about $100 to change over. Plus I could change to 175 mm cranks, which I知 more comfortable with.
    Your frame is flexing, not your crank arms or crank axle. This flex is the reason that whenever frame manufacturers put brakes in the bottom bracket area riders get annoyed.
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