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  1. #1
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    Shimano external bottom bracket compatibility

    Is the Shimano external bottom bracket on XT 760 crankset compatible with other cranks like Race Face, FSA and Truvativ? I'm thinking of getting a 5-bolt crank that uses an external bottom bracket for singlespeeding. So far the only 5-bolt crank that uses external bottom bracket are road or track cranks from FSA and Truvativ and also Shimano. Will there be an issue if I use a road crank for singlespeed MTB application? Thanks for the help.

  2. #2
    Nightriding rules SuperModerator
    Reputation: crisillo's Avatar
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    Rcae Face, FSA and shimano are interchangeable...I think Truvativ uses a different size cup...


    about using a double road crank, if it is an outboard bearing type you might have problem clearing the chainstays

  3. #3
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    Quite right. Race Face X-Type, FSA MegaExo and Shimano Hollowtech II bottom brackets are all compatible with one another - they only differ in the number of spacer rings you have to use.

    TruVativ GXP crankset spindles are "tapered" (ie the diameter is smaller on the non drive side), so the left bottom bracket bearing cup makes it incompatible with the other outboard bearing systems.

    Using road cranks for single speed mtb purposes is no problem as long as you don't intend to do a lot of big jumps or drops.

    Chainstay clearance issues can be avoided if you use a small BCD crankset with a single chainring that is 38T or less. This also gives you a perfect, if not an almost perfect chainline.

    Make sure that your chain tensioner (if you use one) can reach past the midpoint of the splined freehub body. It's good to have this reach capacity when you're experimenting with chainlines.

  4. #4
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    Thanks for the help guys. I think the only option for me to re-use my existing Shimano XT BB is to go with a road crank (the only ones with 5-bolt arms). By the way I've measured the center to center distance between holes on my Boone chainring and it came out as 55.3 mm. According to Sheldon Brown, if this number is multiplied by 1.7 for 5-bolt, that will be the BCD. The seller of the Boone chainring told me it is 110 BCD. If I apply Sheldon's formula it is 94 BCD. Do you think I should trust more Sheldon as he is an authority when it comes to bike measurements? Thanks.

  5. #5
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    Reputation: Bikinfoolferlife's Avatar
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    Sheldon I trust but double check your own calculations just in case (I'm not saying you goofed, I didn't check)....but if your calculations are correct then you're really out of luck as I don't think there are any 5 arm external bb 94 bcd cranks out there at all...
    "...the people get the government they deserve..."
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  6. #6
    anyone else smell that?
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    surly mr. whirly

    http://www.jensonusa.com/store/produ...+Crankset.aspx

    spendy, but from all accounts very nice.
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  7. #7
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    I hadn't seen those, nice but indeed a bit pricey. I don't suppose they've got a set of 58mm bcd holes on the back in case you want to run a granny? Looks like there's something there, not sure what though.
    "...the people get the government they deserve..."
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  8. #8
    Nightriding rules SuperModerator
    Reputation: crisillo's Avatar
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    Quote Originally Posted by Bikinfoolferlife
    I hadn't seen those, nice but indeed a bit pricey. I don't suppose they've got a set of 58mm bcd holes on the back in case you want to run a granny? Looks like there's something there, not sure what though.
    with the whirly you can "build to order" too

    choose the arms , spindle and spider

  9. #9
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    I like the Mr. Whirly

    I'm leaning now to just order the arms, spider and spindle for the Mr. Whirly. Buying from Universal Cycles it will set me around 220 USD shipped for the set. Now does anyone knows what is the type of crank fixing bolt to be used for this set? Also does it come if you buy the crank arm or the spindle? I have another option and that is a brand new RF Turbine ISIS with BB from an LBS for $249. I was hoping if I can't get an ext. BB compatible set to find a RF Turbine in square taper but those seems to be really hard to find.

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