bottom bracket swappability?- Mtbr.com
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  1. #1
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    bottom bracket swappability?

    I am buying a Fantom Comp frame from a forum member. I have a hard tail now and want to swap all the components over to the Fantom frame. How can I find out if the bottom bracket from my current bike fit into the Fantom? My current bike is an '07 Specialized Rockhopper Disc. Also what other components should I make sure will swap over?

    Thanks
    Zack

  2. #2
    Trail Ninja
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    There are a few BB standards out there*, but a majority are 73mm wide nowadays. Seatpost diameter varies more, between 27.2 and 31.6 I believe. Most Motos come with 27.2mm seatposts and come with standard 73mm English threaded BB shells.

    *68mm, 73mm, 83mm wide. Interfaces: square taper, octalink, isis. If you use the same BB crank combo, interface shouldn't matter

  3. #3
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    thanks. I looked up the head tube and seat post measurements. head tube is the same but seat post is little different. Fantom is 31.6mm and the Rockhopper is 30.9mm. Does this mean I will need a new seat post?

  4. #4
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    Ah, the Comp DS and not Comp HT. When you said 31.6, I figured only the full suspension models should have that. I think that one has a 68mm BB shell too, so you may be out of luck on the BB too.

    You can probably run a shim if it's a quality seatpost you like, otherwise it's more advisable to get a new seatpost. Seatposts that run okay with shims long term are usually heavy duty ones like Gravity Dropper, but it's best to get the closest size even with those.

  5. #5
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    When I pull up the specks for the Rockhopper I get this:

    BOTTOM BRACKET
    Shimano ES-25, Octalink Spline, cartridge bearing, 68 x 126mm for 50mm chain line

  6. #6
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    Actually, I take that back. Not sure if the DS Comp has 68 or 73mm, since the official spec isn't listed and can't find any info on someone parting it out or doing something like what you're doing quickly. Newer BBs are made to fit shells of all sizes with spacers, but I doubt you have any of those.

    Your BB seems relatively wide. Might have chainline issues, but it should at least give you chainring clearance (in relation to the chainstays).

    Sounds like an interesting project. Some others may be curious to know too, so keep us updated on how your project goes.
    Last edited by Varaxis; 09-22-2010 at 07:52 PM.

  7. #7
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    On this website
    http://www.motobecane.com/ds/

    it reads
    BB DROP 67.0

  8. #8
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    That's the distance in mm that the center of the BB shell is lower than the wheel axles--actually doesn't sound right either, looking at the pictures, unless they mean sagged.

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