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  1. #1
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    Dumb newbie question about cranks and bottom brackets

    When and if I ever get around to replacing my crank and bottom bracket,,,,If I were to do it as a pair could I go with any style bottom bracket or do I have to stick with the style that is on there now? Sorry for the newbie question

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    You're limited tp matching the BB shell In trms of width and thread, After that the BB and crank need to be compatible with each other.
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  3. #3
    Senior Member MudPie's Avatar
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    1. You will need to match the bottom bracket shell width (probably either 68mm or 73mm) and the spindle length. These numbers may be printed on the current bottom bracket, such as 68x118 (68 mm shell width x 118 mm spindle length). You can also measure these dimensions directly from the frame and existing spindle.

    2. Also, you will need to match the bottom threading to that of the frame. Assuming you don't have an exotic bike, it is probably 1.375"x24 tpi (1.375" diameter x 24 threads per inch). This is by far the most common threading and considered "run of the mill", "garden variety".

    3. You don't have to buy a new bottom bracket and crank set, just make sure the bottom bracket spindle matches the crank arm interface.

    4.. See here for more detail on Bottom Brackets (scroll half way down the page).

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    Quote Originally Posted by MudPie View Post
    2. Also, you will need to match the bottom threading to that of the frame. Assuming you don't have an exotic bike, it is probably 1.375"x24 tpi (1.375" diameter x 24 threads per inch). This is by far the most common threading and considered "run of the mill", "garden variety".
    Also known as "English" "English 68" would be that threading on a 68mm wide BB.

    KeS

  5. #5
    Senior Member CACycling's Avatar
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    Quote Originally Posted by MudPie View Post
    1. You will need to match...spindle length.
    Spindle length will depend on the new crankset and may very well be different from the current length.

  6. #6
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by FBinNY View Post
    You're limited tp matching the BB shell In trms of width and thread, After that the BB and crank need to be compatible with each other.
    Not necessarily. Modern external bottom brackets use spacers for adjusting the width. Most all of them come ready for 73mm bottom brackets and you just use the appropriate number of spacers for a 68mm bottom bracket. You could, and I have, do the same for an internal bottom bracket.
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