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  1. #1
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    Choosing BB/ Crank

    Current upgrades are as follows, SRAM X.0 grip shifts, SRAM X.0 rear derailleur, Shimano XTR front derailleur, Sun Ryno Lite XL rims, wheelsmith stainless spokes, XT 756 disc hubs front and rear, SRAM PG990 9SP rear cassette, SRAM PC-991 9SP chain. The old BB had a shitty heavy steel 122mm square taper spindle, I want to upgrade to an ISIS setup with a new crank as well. I have a 68mm shell and I've been trying to determine the best crank/BB setup to go with to complement the rear drivetrain. I like what I've seen from Race Face and Truvativ, but I am unsure as to what components work well together. I am leaning towards the internal bearing setup and want to keep the BB and crank assembly under 200$ if possible. Thanks for the help in advance.

  2. #2
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    Quote Originally Posted by 98 Giant Rincon
    The old BB had a shitty heavy steel 122mm square taper spindle, I want to upgrade to an ISIS setup with a new crank as well.
    Don't get an ISIS BB. The bearings tend not to last very long.

    Instead consider one of the following: 1) a different square taper 2) Octalink, or 3) an external bearing system such as Hollowtech II.

  3. #3
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    is there any spacing issues I am going to confront if say I wanted to change the spindle length of the BB from 122mm to 113mm or something different? I know that the crank would ultimately have to match the BB, but with the new 9SP rear cassette I want to make sure that the chain spacing will be correct.

  4. #4
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    seriously man don't get isis its so bad... otherwisw any octalink bb is strong like hell !

  5. #5
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    what I really am worried about is the chainline being correct. I have no idea what length spindle I need to get the chain to ride correctly with the rear end, I previously had a 7 speed rear cassette and now it is going to be 9 speed.

  6. #6
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    Quote Originally Posted by 98 Giant Rincon
    what I really am worried about is the chainline being correct. I have no idea what length spindle I need to get the chain to ride correctly with the rear end, I previously had a 7 speed rear cassette and now it is going to be 9 speed.
    Take a look at this page:

    http://sheldonbrown.com/bbsize.html

    If you were to upgrade to an XT-level Octalink (instead of ISIS as you had originally planned), your choices would be either 68x113 or 68x118. Since you started with a 68x122 square taper, perhaps the 68x118 would be the best choice. On the other hand, Sheldon Brown indicates that the 47.5mm chainline is preferred, so you'd probably be better off with a 68x113 BB if you can make it fit. Sheldon Brown says that the 50mm chainline is needed for frames with oversize seat tubes. You'll have to examine your frame to make the best choice.

    If you are committed to using a 50mm chainline, you might as well get a Hollowtech II crankset or one of the other external bearing systems. If you're really not sure which chainline will work best for your bike, an Octalink BB will let you experiment with different chainlines at a lower cost (It'll cost you roughly $35 per BB cartridge.)

  7. #7
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    thanks a lot KevinB I'll go about measuring my frame as soon as the rims and cassette get here next week, I think it will give me a better idea of what my chainline should be if I measure off the rear cassette as is shown on the site you referenced.

  8. #8
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    Where did you get the idea that you need to worry about your cassette in terms of chainline measurement? Did you read the info at all?
    "...the people get the government they deserve..."
    suum quique

  9. #9
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    second that

    Quote Originally Posted by KevinB
    Don't get an ISIS BB. The bearings tend not to last very long.

    Instead consider one of the following: 1) a different square taper 2) Octalink, or 3) an external bearing system such as Hollowtech II.

    my isis driveside crank-arm will wiggle if the bolt isn't super tight, and it comes off in my hand with no tools. and this is after one month.

    I just bought a lx outboard bearing style crank ten minutes ago.

    I've heard shimano did the most extensive engineering on their exos, making them more reliable than the other brands who merely copied the design.(i'm not generally a shimano guy)

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