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  1. #1
    Jerry12
    Guest

    How to tell BB length?

    I just grabbed a used crank, so I am going from square to ISIS, but I dont know what bottom bracket go get.
    Current set up is 2007 FELT Q620, crank is truvativ isoflow, frame is 15.5.
    Is there a way to tell what size the bb is, without taking it out, since I dont have the tool yet?
    Or, is there an ISIS bb that will fit many sized that would for sure fit mine?

    mucho thanks!

  2. #2
    mtbr member
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    there are 3 sizes. 68, 73 or 83mm

    83mm is usually for DH and freeride frames.

    there are many bottom brackets that can fit both 68 and 73mm. they come with spacers and stuff to fit both sizes.

  3. #3
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
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    The Truvativ ISIS BB's are all 68/73, so if you go with one of those you'll be fine.

    Otherwise you can simply measure the BB shell width on your bike

  4. #4
    Jerry12
    Guest
    So it would be a 'safe' idea to get a shorter one and use a spacer?

  5. #5
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    ya. but most mtb BB's now adays are 68/73 or 83. so stick with 68/73

  6. #6
    Jerry12
    Guest
    what about spindle length, 113 or 118?

  7. #7
    mtbr member
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    Measure the shell this way.



    Measure the spindle the same way unless you have access to long armed calipers. You will have to eyeball since you can't get it out but you should be able to get within 1 mm.

    Pull the crank arms off and measure from end to end.

  8. #8
    Former Bike Wrench
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    Most (not all) ISIS triple cranks use 113 for standard frames. The 118 axles were often used on single and double setups with chain guides.

  9. #9
    Jerry12
    Guest
    I ordered a 68/113 BB, also talked to Race Face, thats what they recommended for the crank.
    Thanks for all the info!
    cheers.

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