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Thread: Carbon rim ; ERD ; 2x

  1. #1
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    Default Carbon rim ; ERD ; 2x

    About to start lacing my -once in a few years- wheel set.
    Carbon rims with a reported ERD of 590 mm.
    If I check the diameter of the inside rim by sticking spoke heads (not with nipples) across I come up with 593 mm.
    Is that what I should use?

    Plan on lacing x2 with brass nipples.
    If spoke length difference L/R from the calculator is 1 mm , do I really need a different spoke length?

    Only thing I'm afraid of is bottomming out on the nipple.
    Is a longer nipple more or less prone for this?

    Should be the easiest wheel I ever build because I can not believe how stiff that rim is (35 mm wide).

    Strength should not be a concern in any way, since I was not able to kill a Crest wheel with revolutions that I forgot to "cross under". (No beer drinking this time when working).
    Thanks in advance for advice,
     

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    Default Re: Carbon rim ; ERD ; 2x

    Park Tool has a how to on their site about measuring ERD: Measuring Effective Rim Diameter | Park Tool
    The Wheel Pro book (https://www.wheelpro.co.uk/wheelbuilding/book.php) has a similar method tool described in the book, but you cut your measurement spokes down to 200mm and then measure the distance between the ends across the wheel (the two spokes are bound together across the center with an elastic to keep things in place while measuring). I have used this method a couple times and it works quite well. Its probably a good idea to measure a few pairs of holes just in case the wheel isn't perfectly round.

    You bought spokes for a 590mm ERD already? If you have, then the spokes are going to be a bit short assuming your 593mm measurement is correct. I can't comment on if longer nipples will help or if short spokes will cause reliability issues, but I can say that you will likely have a bit of a hard time building them since the nipple driver won't release until the spokes have excess tension on them. You could probably build a nipple driver with an extra long nub in the center that is tailored to your build to get around this (a bit of a bodge).
    If you haven't ordered them yet then calculate their length from your ERD measurement not from the manufacturer spec.
    - Brad Comis

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    Default Re: Carbon rim ; ERD ; 2x

    You need to measure with nipples, with the spokes in the nipples where you want them to end up - that way you know how to round the calculated number to a number you can actually purchase (unless you've got someone who can cut/thread spokes for you). What you're really measuring isn't the diameter of the rim, but the diameter the ends of the spokes reach.

    Also, in my mind, the 'perfect' spoke length shown on the park site - that's really the minimum length. Perfect is end of the spoke flush with the top of the nipple.
    Last edited by dgaddis; 02-12-2018 at 02:44 PM.
    Dustin Gaddis
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    Default Re: Carbon rim ; ERD ; 2x

    If you use d-light spokes, you can go longer without fear of bottoming out. I would use the 593 number. Sapim nipples have the same thread length so it won't matter for bottoming out. DT nipples might have longer threads.
     

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