Wheel build - bladed spokes?

Discussion in 'Cycling Equipment' started by padawan, Dec 29, 2005.

  1. padawan

    padawan New Member

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    I'm having a rear wheel built with a PowerTap. Because of the expense (and the value in viewing the data) I will train and race on these. Some of my racing is 1/2 Iron and Iron distance triathlons. So I want a solid wheel that is still reasonably aero.

    I've decided on the rim (Mavic CXP33) and the hub is taken care of but I don't know much about spokes. My questions...

    1) Is there a significant aerodynamic gain to bladed over butted spokes?
    2) I'm planning to have it build with 32 holes and 3x lacing for strength - any problem doing that with bladed spokes?
    3) Any other factors I should consider in my decision?

    Cheers
     
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  2. Retro Grouch

    Retro Grouch New Member

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    Some spokes are more bladed than others and require slotted holes in the hub flanges. DT aero speed spokes or Wheelsmith oval aero spokes will work with conventional hubs.
     
  3. daveornee

    daveornee New Member

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    1) what would you call "significant aerodynamic gain"?
    2) No problem interlacing bladed spokes?
    3) Cost per spoke is higher, spoke alignment and tension testing is more challenging, Sapim CX-Ray spokes are used in standard hub holes and have the highest tested fatigue resistance, bladed spokes are not as stiff as most other butted spokes. Sapim makes a spoke holder for CX-Ray and their other aero spokes.
    See:
    http://www.sapim.be/index.php?st=products&sub=spokes&category=3959&id=3340&detail=aero
    &
    http://www.sapim.be/index.php?st=products&sub=spokes&detail=fatiguetest
    I sometimes build with CX-Ray spokes. They take longer to build with and are ~4X more expensive than Sapim Race DB 14/15 spokes.
    dave at ornee dot net
     
  4. padawan

    padawan New Member

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    Without doing all the complicated math on drag coefficients, etc. (not that I could if I wanted to :) - I wanted to get a feel on the time difference it might make on an Ironman, all other things being equal. If it was a matter of seconds, I probably wouldn't worry about it - but if it was 5 or 10 minutes...

    I've never ridden with bladed spokes but many wheel manufacturers seem to be using them in combination with their aero rims. It could be just marketing. Maybe the aerodynamic advantage over butted spokes is minimal.

    Any thoughts?

    I've talked to a couple of people regarding the build and they use DT spokes so I was looking at the Aero Speed or Aerolite.
     
  5. Weisse Luft

    Weisse Luft New Member

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    Bladed spokes at high tensions need special care because they have limited torque resistance and can "corkscrew" easily. I have made a jig to "unload" the rim in the vicinity of the spoke I am adjusting to aleviate this problem...works for regualr spokes too. Basically, you need to apply a load to the rim in excess of the normal road load.
     
  6. daveornee

    daveornee New Member

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    Read some John Cobb aero articles, NASA testing, and ones like this one from Zipp:
    http://www.zipp.com/tech/documents/Anoteonspokeshape_000.pdf
    & these:
    http://www.bicyclesports.com/Aero_Articles.html
    &
    http://www.sheldonbrown.com/rinard/aero/aerodynamics.htm
    You are on the right track to improve aerodynamics, but I think that the difference in rear wheel spokes between bladed and round butted is in the seconds category for 1/2 Iron distances.
     
  7. John M

    John M New Member

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    Don't you think that the round spokes also wind up at high tensions but that the it is more visually obvious with the bladed (or oval) spokes because of the elongated profile? A few years back, when I was still building wheels regularly, I felt that my wheels with aero spokes probably ended up with less spoke wind up, or "corkscrewing" as you call it, than wheels with round spokes. I assumed that the round spokes were also twisting at high tension but just that it was hard to see.
     
  8. artmichalek

    artmichalek New Member

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    You may not be able to see it, but you can certainly feel it if you turn the nipple in the other direction. There's often quite a bit of backlash before it starts to loosen.

    As for the aero drag difference, it's small and it depends on how "bladed" the spokes are. An oval shape like the CX-Ray or Aerolite is optimum. Any aspect ratio over 2.5:1 and the drag coefficient goes up. I would have to agree with Dave's estimate of a few seconds over a half Ironman.
     
  9. Adam-from-SLO

    Adam-from-SLO New Member

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    I always thought bladded spokes were ment for wheels consisting of 12-20 spokes(no more then that) to reep any kind of aero benifit/advantage. On a CXP-33... it might come in a 28-hole.

    If you could get your hands on some CXP-30 28 or 32-hole rims.... and lace them up with oval spokes... that would be a great way to go.
     
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