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  1. #1
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    New question here. Cranks from ebay now what BB to get?

    I purchased a set of XT M752 octalink cranks and intend to use them on a Rush frame. It looks like the ES71 BB is the one to use, but am unsure of the other variable - 68x113 or 68x118. I can't quite get the whole answer in a search.....

  2. #2
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    If you don't get an anwser here, check your frame manufacturers website to see what they recommend for thier frames. If you are replacing your crank and BB, just measure the one that is currently mounted. Sorry I don't have the exact anwser for ya.

  3. #3
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    You are correct that the XT M752 does use an ES71 or ES51 BB. The first number of the BB is the BB shell width of the frame. Your bike will have either a 68 mm or 73 mm wide BB shell width, you will need to measure this on your bike. The second number is the axle length, the 113 mm axle length gives a correct chainline of 47.5 mm and the 118 mm axle length gives a bad chainline of 50 mm. ONLY select a BB with a 118 mm axle length if you need the extra clearance between the crank and chainstays on the bike such as on burly long travel bikes. Most bikes work with a 47.5 mm chainline and this will result in the best shifting performance.

    On a side note, all of the external BB cranks come with a 49-50 mm chainline just so the manufacturers only have to produce a one-size-fits-all crank. Most people complain about poor shifting performance and a lot of people are off-setting their cranks to the non-driveside just to obtain a 47.5 mm chainline, so it does matter.
    There is no added value to my participation - in fact, just more confusion.

  4. #4
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    Thank you

    Thanks for the info. That helps greatly - appreciate the explanation also. It makes me wonder tho, is there any appreciable difference between the ES 71 and 51? Or are they like XT and LX.....

  5. #5
    Bad Case of the Mondays
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    Quote Originally Posted by ToastR
    It makes me wonder tho, is there any appreciable difference between the ES 71 and 51? Or are they like XT and LX.....
    Yep, pretty much XT/LX. I always go with the higher end bottom bracket hoping that it will last longer (no real data to back it up) since bottom brackets are a bit more of a pain to change.

  6. #6
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    The ES 71 (XT) weighs about 10 grams less than an ES51 (LX) and comes with an aluminum non-driveside cup instead of a plastic non-driveside cup.

    Durability will probably be about the same, but this is just speculation
    There is no added value to my participation - in fact, just more confusion.

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