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  1. #1
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    spoke calculation problem

    I am building a trials wheel for a friend:
    *Rockman single-wall rim with ERD of 543
    *Try-All K2 hub with 45mm flanges and 36mm offset
    32 spokes

    if I plug that into a spoke calculator, i get 265mm spokes. however, the rim is super wide and the spoke holes are drilled pretty far apart across the rim. I think my calculation assumes that the spoke holes are in something close to a straight line. these holes are about 2 cm apart across the rim, which leads me to believe that I need slightly shorter spokes. is there a way to calculate this? there's little room for error considering this is a single-wall rim.

    spoke calculation problem-large_rockmanrrsw.jpg

  2. #2
    transmitter~receiver
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    If you post up all the hub dimensions, I can show you the spoke calc.

    Alternately, the way to get around offsets in a calculator that doesn't allow for them is to reduce the center-to-flange hub dimension. So if your center-to-flange for the hub is 36mm and your spoke holes are offset 1 cm (10mm) from the centerline of the rim, plug in a hub offset of 26mm to get the correct spoke length.

    If you have the rim in hand it is definitely worth measuring the ERD yourself rather than relying on a mfr number.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  3. #3
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    This is straight forward trig ((265*265)-(10*10))^.5= 264.8 any reasonable combination of hubs and rims will be less than 1mm shorter. You can file down 2mm off the spokes use a diamond fingernail file less than 1 dollar to clean up the threads. There is about 1mm effective difference between wheelsmith and dt regular nipples so don't panic if it is a bit off.
    "Dish is illogical." Spoke of Vulcan.

  4. #4
    transmitter~receiver
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    Quote Originally Posted by zerodish View Post
    This is straight forward trig ((265*265)-(10*10))^.5= 264.8 any reasonable combination of hubs and rims will be less than 1mm shorter. You can file down 2mm off the spokes use a diamond fingernail file less than 1 dollar to clean up the threads. There is about 1mm effective difference between wheelsmith and dt regular nipples so don't panic if it is a bit off.
    wrong.
    your approach is incorrect so your answer is as well.
    not so straight forward I guess.

    example:
    45mm flange
    offset of 36mm
    rim with an ERD of 540mm

    the difference in spoke length is 1.1mm for a 10mm offset toward the flange versus ceterline drilled.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  5. #5
    offroader
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    subscribed... I have the exact same question.

  6. #6
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    Quote Originally Posted by CupOfJava View Post
    subscribed... I have the exact same question.
    the question is answered above.
    if the offset is toward the flange you are calculating, reduce the center-to-flange dimension by the offset. if the offset is away from the flange you're calculating, add it to the c-t-f.
    if you post up all your dimensions I will run the calc for you (my calculator allows for input of offset).
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  7. #7
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    I got this simple answer from the friendly folks at Tarty bikes:


    You can simply measure the offset of the spoke hole from the centre of the rim, then subtract that number from the hub offsets

  8. #8
    transmitter~receiver
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    Quote Originally Posted by mack_turtle View Post
    I got this simple answer yesterday in the first reply to my thread
    FIFY
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  9. #9
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    You could also have just read the product description for this rim at tarty bikes. It says "- ERD: 543mm, spoke hole offset 9mm (for spoke calculation subtract 9mm from hub offsets)."

  10. #10
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    i didn't find that link until later, i got the photo from a google image search. my friend just handed me the rim and told me the ERD is 543. the answer was foolishly simple though.

  11. #11
    Nouveau Retrogrouch SuperModerator
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    spoke calculation problem

    Quote Originally Posted by zerodish View Post
    ...You can file down 2mm off the spokes use a diamond fingernail file less than 1 dollar to clean up the threads. There is about 1mm effective difference between wheelsmith and dt regular nipples so don't panic if it is a bit off.
    No, you can not just file down the spokes to shorten them. You will run out of threads.

    I have never noticed any difference in DT and WS when building, and I have mixed them on the same wheel.
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