Building a 20 spokes powertap wheel?

Discussion in 'Cycling Equipment' started by loaasvold, Oct 7, 2012.

  1. loaasvold

    loaasvold New Member

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    I just broke my Cosmic Carbon wheel with powertap hub, so now I'm stucked with a powertap SL hub for use on a 20 spoke wheel. Any idees on how i can build up a new wheel without spending a hole lot of money?
    Rim and spoke type?
     
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  2. alienator

    alienator Well-Known Member

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    I'd recommend hitting eBay and looking either for an old style Zipp 404 clincher (the one that preceded the Firecrest. It had a CF cap on an alloy rim) or for a used or new rear Cosmic Carbone. I think those are likely to be the best options. You can also look at the el cheapo generic aero rims out of the Far East, but I'm hesitant to give those a thumbs since it doesn't appear that many of those companies have used any of the modern methods of CF clincher construction that maximize the clincher's tolerance to heating from braking.
     
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  3. alfeng

    alfeng Well-Known Member

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    FWIW. If your budget is a factor then just relace the hub on ANY 20h 700c rim ...

    Determine whether you need new spokes by measuring the Effective Rim Diameter & using almost any online spoke calculator ...

    If the old spokes are too short (or, damaged), then you won't have an option ...

    • there are at least two schools of thought with regard to re-using spokes ...
    • do & don't ...
    • if you fall into the latter group then buy new spokes ...
    • I recommend straight 2.0 gauge spokes ...
    • a lot of people have bought into the notion that double-butted spokes are better without (IMO) truly understanding why the advantage is probably outweighed by what I feel is a disadvantage


    Even if you are able to reuse the spokes you may want to buy new nipples.

    As noted, eBay may be your best source for whatever type of rim you opt to use.
     
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  4. vspa

    vspa Active Member

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    could you please recommend one or two of those spoke calculator websites
     
  5. alienator

    alienator Well-Known Member

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    Hmmm. Both the science/engineering and Sheldon Brown favor double butted spokes: [IMG ALT=""]http://www.cyclingforums.com/content/type/61/id/274458/width/500/height/1000[/IMG]
     
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  6. vspa

    vspa Active Member

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    how did you break it ?
     
  7. alienator

    alienator Well-Known Member

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    Spoke calculators online: http://www.prowheelbuilder.com/spokelengthcalculator/ http://www.sapim.be/spoke-calculator http://www.dtswiss.com/ And one to download from Damon Rinard: http://sheldonbrown.com/rinard/spocalc.htm
     
  8. vspa

    vspa Active Member

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    thank you
     
  9. alfeng

    alfeng Well-Known Member

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    Quote:Originally Posted by vspa .
    could you please recommend one or two of those spoke calculator websites


    FWIW. I used to use Dan Halem's excellent (IMO) Spoke Calculator; but, its host went away a few years ago and he has chosen not to (AFAIK) restore it anywhere ...

    As a consequence, I have been using the limited-but-exceptionally-easy-to-use SPOKULATOR (there are more obtuse calculators ... ease of use is a good thing, IMO)

    http://houseof3d.com/pete/applets/wheel/appwheel.html

    See my earlier comments here:

    http://www.cyclingforums.com/t/488224/my-spoking-attempt-failed
     
  10. alfeng

    alfeng Well-Known Member

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    First, I want to say without equivocation that Sheldon Brown's untimely death was a great loss to the cycling community ...

    But, Sheldon Brown was wrong on more than one point ...

    And, I believe that whether he-and-others were-or-are wrong with regard to which spokes a wheel should be laced with is open to debate; so, I'm glad you chose the word "favor" because that leaves some eventual wiggle room ... for you.

    Now, I believe that YOU are confusing the "scientific method" with "science" -- the only "settled science" is the hollow declaration made by people like the Environmentalists (and/or, mouth pieces for the Democrats) who insist that "Global Warming" is real and that people who don't subscribe to that particular flavor of Koolaid are cretins-or-similar-knuckle-draggers.

    And, as far as engineering, well, YOU seem to have forgotten an example which I believe that you once cited -- that is, the Tacoma Narrows Bridge. THAT was certainly engineered using accepted formulas & beliefs. Certainly, with that example in mind, one may suppose that engineering can be suspect EVEN IF after the fact.

    • YOU once cited the suspension on your motorcycle -- THAT is, vertical motion -- when the discussion at that time was about lateral stiffness ....
    • Or, were-and-are you somehow suggesting that a rider wants a bike which isn't laterally stiff?
    • If so, then to translated from auto racing, wouldn't tall sidewall automobile racing tires be the norm rather than minimal sidewall tires?!?

    That is not to say that there ISn't a place for double-butted spokes -- however, IMO, double-butted spokes are the emperor's new clothes of cycling -- IMO, their primary benefit is to the weight weenie AND for the wheelbuilder.

    In the former case, there is a reduced weight to the wheel ... but, why not use those even flexier Ti spokes, then?

    Of course, double-butted spokes cost more so the wheelbuilder can probably up-charge a greater premium for lacing than the actual cost differential ... after all, THAT would only be fair because s/he possibly does not keep double-butted spokes in his/her inventory.

    If, as you and others are correct that a double-butted spoke are "effectively more elastic" than a straight gauge spoke, then tell me why the stretching & "compression" isn't introducing premature fatigue. How many times can you stretch a rubber band?

    Most spokes apparently fail at the J-bend ... the reason can probably be attributed to the motion of the hub in relation to the rim which I would think would be exacerbated by the greater "elasticity" of the double-butted spoke.

    Maybe ...

    Maybe not.

    There's more, but the bottom line is that 'I' really don't care if a person prefers a laterally flexy wheel because they have bought into the myth of the double-butted spoke being better ...

    If 'I' were only cruising in the neighborhood and/or down-to-the-coffee-shop then I would want-or-favor the bling-factor which double-butted spokes provide ...

    But, since a portion of my riding involves moderately high speed descents, I would rather have wheels which are not laterally flexy.

    To each his-or-her own!
     
  11. alienator

    alienator Well-Known Member

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    Ignoring your political BS, the reason that the increased flexing in the thin section is happening in a place with no stress risers. The ends of the spokes, the areas that typically break, are where the stress risers are located. The center of the spoke doesn't stretch enough to exceed its critical stress. It operates, despite the stretching, inside the elastic region of its stress-strain curve. I don't know of any "bling" factor associated with butted spokes, but I do know that talking about doesn't support your claim at all. The Tacoma Narrows Bridge failure was a failure in design not in theory underlying engineering, not in the science. More importantly, the Tacoma Narrows Bridge has nothing whatsoever to do with butted spokes vs. straight gauge spokes. It's a red herring. You don't understand motorcycles from engineering point of view either.......oh, and like your bridge comment, the motorcycle comment is also a red herring......but let's entertain it for a moment. First you are correct that motorcycle suspension does function in the vertical plan of the motorcycle. What's important to realize is that when a motorcycle corners, it's wheels aren't laying flat on the ground. They are oriented at some angle to the ground that is between 0° and 90° (again, that angle is with respect to the ground). As such any force--say from hitting a bump--put into the tire will have component that is perpendicular to the plane of the wheel and parallel to the line along which the suspension works. If you don't understand why this is, google "vector components". As such the suspension will move, but remember there is also input into the side of the tire/wheel. It's desirable to have a bit of flex in that direction to absorb that input. There are other reasons for having flex engineered into frame that have to do with managing traction and providing rider feedback. It's pretty obvious that a perfectly stiff motorcycle would bounce off of bumps and lose traction. As a matter of fact the same would happen with a bicycle. You don't hear people raving about the performance of disc wheels on bumpy roads or while cornering, and disc wheels are the closest bicycle analogue to perfectly rigid wheels. If you'd like though, feel free to go through some high speed , tight corners on disc wheels. You claim about wheels laced with butted spokes being laterally flexy doesn't support you either as you have no evidence that such wheels are laterally flexy. My double butted spoked 24/28 2x wheels with 25mm high rims performed excellently for me and my 175 lb carcass, my 16.5lb bike (so that's 191.5lbs if you're keeping track), at 45-50mph curvy, mountain descents--some on bumpy pavement-- in Tucson. They tracked true with no fuss at all. That's not a scientifically derived result, but neither is your "laterally flexy" claim.
     
  12. alfeng

    alfeng Well-Known Member

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    Name another instance where you have read or heard the phrase "settled science."

    There is no such thing ...

    Regardless of one's point of view, the phrase is oxymoronic.

    BTW. If YOU are amongst those who embrace "Global Warming" as espoused by Al Gore, et al, then (IMO) that demonstrates a lack of critical thinking on your part ...

    The Bridge would not have collapsed under normal conditions ... wrong presumptions, wrong conclusions.

    TRY THIS:

    • GRAB four adjacent spokes on a properly tensioned 36h wheel & see how much deflection occurs ...
    • GRAB four adjacent spokes on a wheel with double-butted spokes (preferably 36h & properly tensioned for the sake of comparsion, but fewer spokes would simply amplify the results and make the example more evident) & see how much deflection occurs ...

    Zero lateral deflection may not be good, but that doesn't mean that a flexy wheel is better.

    How much deflection do you want?

    To each his own.
     
  13. alienator

    alienator Well-Known Member

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    Let's be clear, Alfred, I don't give a damn about your politics. Your politics are a red herring as already stated and do absolutely nothing to prove your "argument". If you can't organize your thoughts well enough to realize politics have nothing to do with wheels, you need some help. Second, I never used the words "settled science", but there certainly is nothing new about the science and engineering behind spoked wheels. If you've got some idea that theories behind the engineering and science are wrong, then feel free to prove them wrong. Good luck with that. Your test is a meaningless test. It doesn't tell you anything about the function of a wheel. I've made no claims about how much lateral deflection is ok. Further it has been shown that stiff wheels also laterally deflect: a lateral load at the rim tangent to the contact patch causes deflection opposite the load direction at the top of the rim.
     
  14. alfeng

    alfeng Well-Known Member

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    You know, I wouldn't have cared about YOUR politics, either; but, IF you happen to be an adherent of the fore mentioned myth then it shows a general lack of critical thinking & possibly a great deal about your general thought process.

    I was just using the example of so-called "Global Warming" as an example of something where the term "settled science" has been used ... singlularly used, as if to give it greater credibility NOT UNLIKE your remark "Hmmm. Both the science/engineering and Sheldon Brown favor double butted spokes:"

    WAIT!
    What?!? OH, I see!! So, when you wrote "science/engineering and (invoked) Sheldon Brown" YOU were simply blowing smoke in an effort to add credibility to your now-known-to-be-idle cut-and-paste remark. Is THAT right? If you weren't blowing smoke, then regardless of what you may think you wrote, YOU were implying that the "science" of bicycle wheels (as you seem to be implying, again) IS what has been suggested by those whose pronouncements on the topic you apparently embrace otherwise, why else would you include the "clipping"? So, while you may not have directly used the phrase "settled science" you were certainly implying that there are no other interpretations. If THAT's not what you were implying, then you'll just have to dumb-it-down for us plain folk. BTW. I hope you realize that one of the reasons (probably, the primary reason) that the Tacoma Narrows Bridge failed is because the side loads from the winds were not taken into account ... not unlike the failure of many who talk about bicycle wheels not taking into account side loads ... Heck, I'll go out on a limb and say that people who have had problems with front end shimmy (presuming their headset is properly adjusted AND their fork is true, of course) might have a low count & probably double-butted spoked front wheel.
    Quote: Originally Posted by alienator [​IMG]

    Your test is a meaningless test. It doesn't tell you anything about the function of a wheel.

    OY. What about Swanson's trivial-weight wheel deflection test from a few years ago?

    • Were you amongst the individuals who thought it was potentially meaningful?

    Regardless, weren't you the individual who posted a fairly comprehensive table which compared rim stiffness, or something along those lines?

    So, are you saying that all static test are meaningless?

    What about the arbitrary test which MAVIC ran which you have cited more than once in the past?

    • you may have noticed that a lot of Pro riders "open" their rear brake caliper's quick release ... would those riders have noticed a difference in the variety of wheels which were tested if their rear brake caliper's quick release had not been in an "open" position & therefore possibly scrubbing the wheel's brake surface?
    • that is, could lateral wheel stiffness, or lack of, matter if the rear brake caliper is in its "neutral" position?

    Yeah. Walk it back ...

    Keep walking.
     
  15. alienator

    alienator Well-Known Member

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    I see you can't construct an argument without tossing political insults around. I also see you are unable to address the technical aspects on point. It's impossible to not see that still do not grasp that a bridge failure has nothing to do with a bicycle wheel, not even close. Given even see something as small as that, it's unlikely you'll be able to carry on a technical discussion.
     
  16. CAMPYBOB

    CAMPYBOB Well-Known Member

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    Now, I believe that YOU are confusing the "scientific method" with "science" -- the only "settled science" is the hollow declaration made by people like the Environmentalists (and/or, mouth pieces for the Democrats) who insist that "Global Warming" is real and that people who don't subscribe to that particular flavor of Koolaid are cretins-or-similar-knuckle-draggers.

    You had me at enviro-whackos!
     
  17. dhk2

    dhk2 Active Member

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    alfeng, you stated that Sheldon Brown was wrong, but never stated if you think his arguement above for DB spokes is wrong. Understand you may dislike DB spokes for other reasons, but would like to know if you disagree with the above statements, and if so, why.

    Note, I agree with his statements, in theory. But don't know whether the additional stretch of DB spokes makes any real-world difference in the life of the rim or not. I have had a couple of rear wheels built with straight-gauge spokes which failed around the spoke holes, but of course that proves nothing much.
     
  18. CAMPYBOB

    CAMPYBOB Well-Known Member

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    My straight 14 Ga. 32H/3X Mavic Open Pro's built on Campy Record low flanges just went over 25,000 miles (probably over 30K) of abusive riding on crappy Ohio roads without so much as a touch-up trueing.

    That doesn't prove much of anything anything, either.

    But, add that to all the 14 Ga. straight spokes on all the various wheelsets I've used over the years and I call bullshit on the theory that they cause cracking. Junk rims and trash wheel building causes cracking IMO.
     
  19. dhk2

    dhk2 Active Member

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    Yep, my wheels which cracked had 32 spokes, 14 ga st, but were cheaper rims. First one was the old Matrix ISO rim, built by Colo Cyclist. Spoke tension seemed high to me, and they never went out of true. Probably lasted 4-5K miles tops before rear spoke started pulling through.

    Second failure was on a plain Mavic box rim, MA-40 I think, which was built by a good LBS builder. The rim failed not right at the spoke hole, but cracked at the sidewall corner. Went 12-15K miles before failure. (didn't keep good records then).

    Actually the wheels which lasted me longest so far were Velomax Circuits, built with DB spokes, 24/28, 14/15 ga. Went 30K miles before the rear rim cracked, apparently starting from the valve stem hole. Don't know if the rim would have failed sooner with 14 st.ga. spokes, but as I said before the theory appeals to me.

    Current wheels, DT 1450, are built with bladed "aerolight" spokes.....15/17 ga? They should offer a good comparison if I even put enough miles on to reach end of life Maybe the super-thin spokes will starting breaking before the rim fails on these, but again, that wouldn't really prove the Sheldon Brown theory either.
     
  20. alienator

    alienator Well-Known Member

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    Aero spokes are not really butted spokes. Instead they're straight gauge spokes stamped/forged to their aero shape in the middle. Thus they have the same cross-sectional area as the round ends and act as a straight gauge spoke with one exception: the forging/stamping means there are stress risers created in the area when the spoke transitions from round to aero shaped.
     
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