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  1. #1
    underachiever
    Reputation: misterdangerpants's Avatar
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    Bottom Bracket Width Question

    Okay, so I have a triple crankset that takes a 122.5mm bottom bracket and I want to use it as a double (two outer rings/no granny gear). Should I use a narrower bottom bracket or can I just use the existing one without any issues (i.e. chain line)?
    Last edited by misterdangerpants; 03-06-2010 at 05:11 PM.

  2. #2
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
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    Very dependent on the chainring (middle) and crankarm clearance is with your chainstay...I'd take a close look at how much clearance is there is before looking at a narrower bottom bracket.

  3. #3
    mtbr member
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    Yeah, look at it now and see how much space you have....if you have some room then you might be able to step down to a 118 or 116 spindle. I don't think you really need to, honestly, but you can if you have the room. It isn't going to make much difference and since you're still running a multi-gear setup, your multi-gear chain will have plenty of flex over the distance to keep thing running well. You should be able to turn in the low-limit screw on the front derailleur to set it up properly...if it's too short you can substitute a slightly longer screw or look for an older 2-ring model.

  4. #4
    underachiever
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    Well, the reason I ask is because I haven't purchased the bottom bracket yet so I can't use the recommended size as a reference.

  5. #5
    On MTBR hiatus :(
    Reputation: Speedub.Nate's Avatar
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    With only a 6mm gap between chainrings, you're looking at a spindle length difference of only 3mm center a 2-ring setup vs. what you currently have (assuming the middle of three rings is correctly centered on the cassette). So that would be a spindle 119 to 120, if available.

    But also consider how you want to use the middle ring. Do you envision using it across the entire cassette, while reserving only the smaller cogs on the cassette for the big ring? If so, leave it where it is.

    On the other hand, if you want to "optimize" the middle ring to the lower range, and extend the range of the big ring to another cog or two, then bumping it in is justified.
    speedub.nate
    MTBR Hiatus UFN

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