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  1. #1
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    Bottom Bracket Replacement on Trek Soho S

    Hello All,
    I'm wondering if any of you mechanics have any experience dealing with the Trek Soho S and more specifically their bottom bracket set-ups. I must replace the cranks and due to the change the BB must be replaced as well ( I think ). I can't find anywhere the type of information I need to make this work myself. So I'm here asking for your help.

    Would appreciate any appropriate information for replacing the Cranks/BB on a Trek Soho S.


    My problem in further detail ( for those interested )
    I have a Trek Soho S which I am planning to sell. Before I can sell it though I know some parts need to be replaced. One of these being the crank set. I accidentally stripped one of the crank arms when doing a routine maintenance. My solution at the time was to thread the pedal through the opposite side of the crank arm and re-thread the crank in that way. It has worked well and I haven't had any problems but I don't feel comfortable selling the bike with those cranks on it.

    I have been looking at new cranksets and have thought to buy the SRAM S100 1.1. Mainly because SRAM is kept in high value here, the price is reasonable enough, I can get it from reliable dealer quickly. It's recommended that the S100 be used with a PowerSpline BB which comes in a variety of sizes. This is as far as I have gotten....

    I have no idea what size bb I need and I can't find the information anywhere short of pulling the cranks off myself and taking the BB out and measuring it. If I have to do that, I can but it's going to have to wait till the weekend and I was hoping to order the parts before the weekend.

    Does any one have any experience with this job on the Soho S? Any help you could throw my way would be appreciated. If I have left something important out, let me know and hopefully I have that information.

    One other thing I was emailing with one of the mechanics from the shop I bought the bike from and the information which they knew was.

    It's british threaded
    the BB shell is either 68 mm or 73 mm
    and nothing said of the axle's length


    Cheers
    Jamie

  2. #2
    Senior Member CACycling's Avatar
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    Following the link you provided, the crankset requires the BB length is 108. I'd assume your BB shell is 68mm but just measure the width to be sure.

  3. #3
    Senior Member
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    Thanks for the reply CAC

    I don't know if I am missing something or thinking something as harder than it really is, I also leave open the possibility that I don't understand the front drive train. But could there be a possibility that the Soho S requires a wider or longer axle than 108 mm and if that was the case then

    1. These cranks would not work on the bicycle because they require a 108mm BB that would be too small in the frames BB shell
    2. These cranks are compatible with longer powerspline BB and I would just need to the proper length and use that with the cranks.

    3. the bb fits but it's shorter by 4 mm and chainline is displaced and no longer optimal

    I stated the above because in a post I read ( which I can't find now ) I remember a guy having bought a BB already and wanting to use these cranks and the replies seemed to point towards that he would be fine using a longer length.

    Man, I'm confused...

  4. #4
    Senior Member CACycling's Avatar
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    For the most part, BB spindle length is determined by the crankset. The 68mm BB shell width is very common and doesn't impact the spindle length (a 108mm spindle in a BB designed for a 73mm shell would result in the chinring sitting the same distance from the bike's centerline as a 108mm spindle in a BB designed for a 68mm shell width).

    The (apparently) recommended 108mm BB spindle is sized based on the offset of the crank itself to yeild a "standard" chainline (placing the chainring the correct distance from the bike's centerline). This doesn't mean you couldn't get away with a longer (or possibly shorter) spindle in your, or other, applications. Just that the 108 is (apparently) the norm. Also, chainline is effected by the build of the wheel and where the cog(s) are lined up in relation to the centerline of the bike.

    Consider the external bearing BBs like Hollowtech II. There are no options for spindle length. You buy the cups based on BB width and threading. The spindle is integral to the crankset, comes in only one length and is designed to provide the appropriate chainline regardless of the frame.

  5. #5
    Senior Member
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    I think that has cleared up most if not all the confusion. You have my gratitude.

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