SS mtb with track transmission!??!?- Mtbr.com
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  1. #1
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    SS mtb with track transmission!??!?

    Sorry to disturb you but I really need some transmission expertise for my first SS. I want to build a freak bike for use on-road. I want:

    1. the transmission simplicity of a SS
    2. the frame of an MTB (already bought Kona explosif)
    3. and the potential speed of a SS roadie/track bike.

    The area of question is the crank/BB. Before I understood enough, bought a shimano XT SS modified crank. I eventually realised that the chain wheels that could fit it were more for offroad and would not easily give a high enough top speed for my type of riding. (There aren't that many hills in London.) Being 6' 2" the lengths are 175mm, which I now see as a potential problem as I plan to mainly ride fixed. I may be wrong but this doesn't seem to fit the 3 point bill?

    I've just started 'noticing' the other end of the spectrum like Suginos, Miches, Strong light, Pauls & Dura Ace which I now really appreciate and I'd like to integrate this end of equipment onto my ride however, there is the potential problem with the mtb frames being a lot wider than typical road/track cycles which could cause problems.
    I have already ordered a pair Goldtec hubs (rear: flip/flop fixed/free) to be built up with DT Swiss 700c rims. What kind of length do I need to look out for in regard to the BB axle and being able to fit a crank, as well as chain line issues? (the shell is a std 68mm x 113mm)
    If the world of square tapers are an option then I'd think about Phil Wood or Royce, is this good or bad?
    Any help greatly appreciated on this one. If you need any more info dont hesitate to ask.

    Best regards

    P.S.
    Not sure if this is correct but I think I read that shimano have brought the external BB technology from mtbs to the road side of things or that it is possible to do do this kind of modification, if so does this mean that Duras and Ultegras may work?

  2. #2
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    I am not sure points 1. and 3. are mutually agreeable? A track bike is 'quick' because it is geared very high - this sort of gear may not be suitable for the more stop start nature of London traffic.

    The chainring should not be an issue - there are third party manufacturers making dinner plates for MTB cranks - the old 110 BCD would be better though. I would stick woth square taper - anything is then possible. I use a Campag Centaur chainset (single ring) on a Surly 1x1 with a UN73BB. That's a 73mm BB with silly wide chainstays to clear 2.7 tyres - works great. Yes in theory Campag/Shimano are not compatible (tapers different) but like many it works perfectly for me.

    I would forget Phil etc - the UN73 is one of Shimano's best ever products, ever.

    175mm is fine if riding fixed wheel. Plenty go 10mm shorter than that.

    I cannot see why you want a MTB frame though - a Surly Steamroller for instance may be a much better bet for your planned use.
    Last edited by felixdale; 10-22-2006 at 09:46 AM.

  3. #3
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    Ive always felt a lot more comfortable with mtb geometry than racer styles.

    I am quite new to a lot of this stuff so I will ask questions about the abbreviations. As for the BB, you're suggesting the Shimano UN 68mm BB?
    If this is correct for my frame what kind of cranks am I open to?

    Is cost the reason for not going with the Woods or Royces?

  4. #4
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    No, UN73 is Shimano's code for their XT level conventional square taper BB. Comes in 68mm or 73 mm (the shell width 73 is just a co-incidence with the model number).

    As here at CRC: http://www.chainreactioncycles.com/M...spx?ModelID=49

    They are true fit in 30 seconds and forget, reasonably light and superb quality.

    You can fit any standard square taper mountain or road crank you like - any Shimano, RaceFace, Middleburn, etc, etc. Length of BB spindle depends on clearance of chain stays and chain line etc.

  5. #5
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    Main concerns that pop up when I read this:

    1. Goldtec hubs on an Explosif: Are they spaced out to 135mm? Standard track spacing is 120mm, so that's a bit of room to squeeze if they are not.

    2. Chainring clearance and chainline: Standard chainline for 120mm hubs and others is around 42mm. On a mountain bike, 42 mm is pretty damn close to the BB, a lot closer than the 52mm that is common for SS mtb's. I think you'd have a real problem with putting road/track cranks on with a 42mm chainline without hitting the chainstay with your chainring. If they are wide hubs, this won't be as much of a problem, but you probably still won't be able to fit a 44 on there without some mucking about. If it is a spaced 120mm hub, you might need to respace and redish in order to get the chainline okay with a big chainring/spider setup.

    An easier way to deal with it would be to just reduce everying: run a 34-12 with some 110 or 4-arm cranks.

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