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  1. #1
    Reputation: awai04's Avatar
    Join Date
    Jul 2004

    30mm bottom bracket design Q - what's the point of a center tube?

    I have often wondered. For examples, the Raceface 30mm bottom bracket comes with a center tube made either of plastic or aluminum to span the distance between the two bearing cups. The Hope 30mm bottom bracket comes only with the cups. Which is a more ideal design? On initial analysis, I would think that the center tube helps distribute forces more uniformly across the entire bottom bracket. Yet between the two bottom brackets, word on the 'net favors the Hope as the stronger of the two. So... does the center tube really do anything useful?

  2. #2
    mtbr member
    Reputation: Mudguard's Avatar
    Join Date
    Apr 2009
    I thought the tube just helped line the crank axle up when you were sliding it through? Rather than having any structural purpose?

  3. #3
    Reputation: Vegard's Avatar
    Join Date
    Jul 2009
    I thought it was for sealing the axle and the sides of the bearings that point inwards from liquid and debris. Whenever I've built my own bikes from scratch I always tossed the sleeve away, never had an issue.

  4. #4
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Yeah, the marketing materials on those bb's (Race Face in particular, where the sleeve has o-rings on it where it snugs to the bb) indicates that the sleeve is simply supposed to keep dirt/water away from the bearings, at least from the inside.

    I used one once. Then for the next bb, I tossed it. *shrug* I don't think it makes THAT much of a difference.

    BB's like Wheels mfg where the sleeve threads together inside the bb shell are different. Those are meant to ensure the bearings line up correctly.

  5. #5
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
    Join Date
    Nov 2007
    I wonder if it's kind of like fork boots: designed to keep crud out but actually keeps it in.

    I usually use the sleeve if the bottom bracket comes with it and don't overworry it if it doesn't, or if I damage it.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  6. #6
    mtbr member
    Join Date
    Mar 2004
    It is supposed to keep water out. When people wash their bikes, the bb fills with water, as most bike manufacturers no longer drill the BB area to drain. If the tube is not installed, the bearings can be sitting in a puddle of water.
    About half of the BB's I service have a substantial amount of water sitting in the frame.

  7. #7
    Reputation: awai04's Avatar
    Join Date
    Jul 2004
    Good to know you guys, thanks. I guess drilling a small drain hole at the bottom would serve as a place where water and dust could *enter* as well as drain, so that's why the detail isn't added anymore? Either way, sounds like regular maintenance is the way to keep our toys turning smoothly.

  8. #8
    Plays with tools
    Reputation: customfab's Avatar
    Join Date
    Jun 2008
    The definitive answer is: the tube between the cups, regardless of material is only there to keep the bearings from being contaminated from inside the frame. If your frame has a sealed bottom bracket shell, which isn't uncommon with modern carbon bikes the tube is absolutely worthless. It won't cause any harm however so don't worry if it's installed. Drain holes in the bottom bracket shell are a great idea, since it's the lowest spot in the frame it will allow any moisture in the frame to drain out. That's a good thing regardless of frame material.

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