bottom bracket bearings sizes

Discussion in 'Cycling Equipment' started by Phill P, Jan 7, 2008.

  1. Phill P

    Phill P New Member

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    What are the size bearings needed for the different style bottom brackets?

    Shimano/FSA/Trek/Scott etc
    Campy UT
    Sram/Truvativ
    BB30

    BB30 sounds good as it gets the bearings in and allows better q factor, but the seal drag must be worse than standard shimano style external bearings.
     
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  2. alienator

    alienator Well-Known Member

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    Well, I think BB30 is another of those things that is a solution looking for a problem. Certainly, there is no stiffness issue with BBs these days. Hell, there wasn't a stiffness issue with square tapers. Also, bearing life isn't really an issue, much, any more. The first external BB bearings had issues, but if you get the right bearings and take minimal care, there won't be any issues.

    Seal drag will be higher in BB30 kit because seal drag increases with increasing swept area on the seal, BUT if a person can turn a crank with one arm tied behind their back, using only a pinkie, seal drag won't be an issue. Seal drag is constant and very, very small.

    The more worrisome problem with BB30 is that bike makers would have to adopt a new standard, which means higher prices and customers being locked into a new thing. Other than being able to market the word "stiff", BB30 doesn't really gain us anything.
     
  3. Phill P

    Phill P New Member

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    Well it seems to be a battle between the shimano/Scott/Trek pressed in bearings at the same width as a "standard" external BB. Smaller bearing, less seal drag (which I still find terrible compared to my campy square taper), but wider so not as good for Q factor. Trek have taken advantage of the wider BB shell as well with the worlds widest down tube for stiffness, but what does that do for aerodynamics??

    Why not do the shimano sized bearings into the BB30 narrower width?

    Anyway main point of this topic was to find the actual bearing dimensions for the different designs. Commonising makes everybody's lives so much easier!!

    Don;t even get me started on the number of different bearing sizes for Shimano and Mavic hubs across the ranges...........
     
  4. Phill P

    Phill P New Member

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    OK....just did some research at boca....
    they have

    UT and shimano 2004+ - 25x37x6 (non standard bearing size!)
    Madone 2008 - 24x37x6 (no shim?.....how can it fit shimano with different ID?)
    FSA - 25x37x7
    Truvativ -24x37x8

    There are people advertising thier bearings will fit Shimano/FSA/Truvativ, and Madones are designed to take shimano cranks, but they are all different sizes!!! How does this work????

    Out of interest
    BB30 30x42x7 (big and heavy)
    Hollowtech 2 25x37x7 (why go non standard from 2004???)

    Is somebody able to explain????????
     
  5. Peter@vecchios

    [email protected] New Member

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    Interesting how this all has progressed. shimano(closely followed by ISIS) decided it needed a stiffer/lighter BB 'system'..mostly for marketing, not for performance. After this new 'standard' flooded the marketplace, it was obvious it wasn't the most reliable, well designed system out there...enter outboard bearing 'system'. Q factor goes up, versitility goes down(small ring hit the frame on that external BB system?.tuff)...now enter BB30 'system'. Innovate(not improve) or die in this flat market. Stiffer, sure, lighter, yep but with numbers small enough to be insignificant. Seal drag?..in spades..gee, I gotta idea, ceramic!! BBs for only $200 when a better designed BB was in order....I gotta idea...loose balls inna cup, with grease and a simple 4 sides, tapered interface.....
     
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