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  1. #1
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    Replacing Crank...Need Help

    I have an older 2014ish Specialized Fatboy with the SAMOX crank. I'm going to convert it to 1x (currently 2x) and in the process I want to shave some weight from it.

    Problem is when it comes to cranks the standards are all over and when shopping I never really know if I'm buying the right thing.

    What measurements do I need to know when buying a new crank?


    I know right now it's in a PF30 BB.

  2. #2
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    PF30 describes what will fit the frame BB shell. Depending on the PF30 BB you have installed, or will install, it will fit either 30mm spindles, 24mm spindles, 24/22mm GXP spindles, or DUB spindles. You need a crank and BB that agree on spindle, and a crank with a spindle that's long enough for the width of your BB. That can vary a lot, particularly on fat bikes. Also, check that the chain line will be OK with the new crank, e.g. the ring clears chainstay and ring is about the right distance from the center-line of the bike.
    Do the math.

  3. #3
    since 4/10/2009
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    Quote Originally Posted by Lone Rager View Post
    PF30 describes what will fit the frame BB shell. Depending on the PF30 BB you have installed, or will install, it will fit either 30mm spindles, 24mm spindles, 24/22mm GXP spindles, or DUB spindles. You need a crank and BB that agree on spindle, and a crank with a spindle that's long enough for the width of your BB. That can vary a lot, particularly on fat bikes. Also, check that the chain line will be OK with the new crank, e.g. the ring clears chainstay and ring is about the right distance from the center-line of the bike.
    not to mention that there are two different pf30 bb types. There's internal bearing versions, and external.

    https://wheelsmfg.com/bottom-bracket..._standard=6859

    External versions are sorta the oddball ones (not as many out there), and IIRC, that's what the Fatboy comes with. Coupled with it being a fatbike, it means you have to be extra vigilant on crank spindle length. Pretty sure the easiest cranks to fit onto this setup are going to be RaceFace's modular 30mm cranks like the Turbine or Next cranks since their spindles tend to be pretty long. Pretty sure you'll need the longest spindle (for 190/197mm rear spacing) and plenty of spindle spacers.

  4. #4
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    Quote Originally Posted by Harold View Post
    not to mention that there are two different pf30 bb types. There's internal bearing versions, and external.

    https://wheelsmfg.com/bottom-bracket..._standard=6859

    External versions are sorta the oddball ones (not as many out there), and IIRC, that's what the Fatboy comes with. Coupled with it being a fatbike, it means you have to be extra vigilant on crank spindle length. Pretty sure the easiest cranks to fit onto this setup are going to be RaceFace's modular 30mm cranks like the Turbine or Next cranks since their spindles tend to be pretty long. Pretty sure you'll need the longest spindle (for 190/197mm rear spacing) and plenty of spindle spacers.
    Thanks - I'm fairly certain the current spindle dia is 30MM as I replaced the plastic BB that came with it with a wheels mfg PF30 - this one specifically. https://wheelsmfg.com/bottom-bracket...-bb-black.html

    I always ride in my big ring of the 2 that it has, so I could just measure the spindle length and get one with the same length right?


    Yes it has about 40mm of spacers on the non-drive side....

  5. #5
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    Quote Originally Posted by jbsmith View Post
    so I could just measure the spindle length and get one with the same length right?
    wish it was that easy. The way RF measures spindles includes the splined bits that interface with the crank arms, IIRC. Though the way they tend to sell them often refers to the rear hub spacing (since that's a number that people are more familiar with).

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    Quote Originally Posted by Harold View Post
    wish it was that easy. The way RF measures spindles includes the splined bits that interface with the crank arms, IIRC. Though the way they tend to sell them often refers to the rear hub spacing (since that's a number that people are more familiar with).
    Ahh - see this is probably why I haven't done this before, but that stock crankset is a tank. Suppose I could call RF...or buy from somewhere that has a good return/exchange policy!

  7. #7
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    A lot of cranks and/or websites don't even seem to list the spindle length? I assume then I should stay away from those that don't as their likely for a non-fat bike?

  8. #8
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    Quote Originally Posted by jbsmith View Post
    ...Suppose I could call RF...or buy from somewhere that has a good return/exchange policy!
    One possibility would be to bring the bike to the LBS and have them get you the part. They'd be responsible for getting the right part.

    You might inquire in the Specialized or Fatbike forums as there's probably members there who have Fatboys and may know specficially what works.

    And, if you haven't yet, check out the Wheels fat bike BB/crank info page:

    https://wheelsmfg.com/fat-bike-bb-tech

    Do the math.

  9. #9
    since 4/10/2009
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    Quote Originally Posted by jbsmith View Post
    A lot of cranks and/or websites don't even seem to list the spindle length? I assume then I should stay away from those that don't as their likely for a non-fat bike?
    I bought my Turbine cranks a long time ago when they were first released (the CINCH version). I had to buy the arms with the standard spindle for 68/73mm bb's, plus the longer fatbike spindle for 170/177 rear ends separately. You might be able to find the arms without a spindle now, and buy the spindle you need separately. But either way, I would expect the sale listing to tell me how the cranks are sold.

    And if I couldn't find the info I needed, then I'd certainly buy from a shop, since I could be certain (the distributors that shops order from tend to supply all of that important info in THEIR listings).

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