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  1. #1
    Soma Lover
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    To Butt or Not to Butt

    Hi!

    First time poster here.

    I'm building up a Soma Double-Cross as a light touring and occasional cyclocross rig. I've picked up a pair of Bontrager Maverick 700c 36 spoke rims at 490 grams each and Ultegra Hubs to build up as the light touring wheelset. I'll have a second set of Open Pros on Ultegra Hubs for cyclocross.

    I'm a not quite but very nearly ultralight backpacker who weighs just 155 lbs. I'm aware that the higher bottom bracket will give the frame a little less than ideal stablility for touring. The bike will also be quite heavy for cyclocross, 21-23 lbs. depending on which wheelset and tires it is set up with.

    Assuming I plan to use a pair of Arkel T-42's on the rear and T-22's on the front:
    Should I use butted spokes for durability?
    Or should I use straight gauge for stiffness?
    Or should I not bother because neither will carry the load?

    Thanx for your opinions in advance,

    Bri
    1,000,000 bicycles equals two megacycles

  2. #2
    addicted to coffee velotimbe's Avatar
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    I build my own wheels, so this mostly comes from experience, and not really science.

    I run straight guage spokes on my touring wheelset, I like the added stiffness.

    Most spokes break on a touring bike at the "elbow", which is the same size whether we have butted or straight spokes. You really should not worry about strength so much, since modern butted spokes are just as strong as straight, just not as stiff. If you want to add stiffness to a butted spoke, you can always tie and solder the cross points.

    For touring I would reccomend 32 straight spokes or 32 butted spokes with a tie and solder.

    36 spokes is not really neccessary, as the pull angles on 32 spoke wheels yield stronger wheels than with 4 more spokes. Look at a 32, you will see two spokes directly pulling against two others. This makes a balanced wheel. 36 has 2 spokes pulling two others at an odd angle, which is not good. I read that somewhere, and it made sense, and after riding both kinds, I sincerely believe it.

    Tim
    gunnarroadiesurlylonghaultruckergiantcypressstgunnarruffiantrekfuel90

  3. #3
    Steel is Real. markw's Avatar
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    So when you tie and solder, how do you fix that on the road? I've never understood it except for keeping a spoke from flailing wildly. My preference is double butted as it builds a slightly lighter wheel without a scrifice in strength. As for breaking, the only spokes I've ever seen break were at the elbow.

  4. #4
    You need a new bike supcom's Avatar
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    In his book, Jobst Brandt claims that butted spokes have a longer fatigue life than straight gauge spokes because the thinner cernter section tends to absorb some of the shock that acts upon the elbow. Since spokes almost never break in the center, the thinner center section is not an issue for strength.

    Brandt claims that modern quality spokes have been tested to break under loads more then three times that which they could encounter in use. This is for forced breaks, not fatigue.

    Based on that, if you accept Brandt's argument, you should spend the extra money to get butted spokes for a touring bike.

    Finally, Jobst addresses tying and soldering and claims that the only benefit of this old practice is to hold the spoke in case of breakage.

  5. #5
    addicted to coffee velotimbe's Avatar
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    maybe it is in my head (again, no science here), but I feel that lateral stiffness is improved with tying and soldering. Not allowing movement at that point is effectively increasing hub flange diameter.

    tim
    gunnarroadiesurlylonghaultruckergiantcypressstgunnarruffiantrekfuel90

  6. #6
    Soma Lover
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    Quote Originally Posted by velotimbe
    I run straight guage spokes on my touring wheelset, I like the added stiffness.
    Rivendell is really high on the rims that I'm using to build these wheels. It seems at this point that the ability of these wheels to carry 4000-5000 cubic inches that amounts to a 40-50 lb. load is not an issue. Does anybody out there disagree?

    As far as my engineering background goes, a butted 36 spoke wheel will be far more durable than a 32 spoke straight gauge wheel. It will also lack about 10% of the lateral stiffness. A straight gauge 36 spoke wheel will have about 10% more lateral stiffness than a 32 spoke straight gauge wheel.

    Has anybody run a pair of wheels similar to this with a similar load and suffered control problems? What kind of load was involved? Were the problems fixed by going with straight gauge spokes or were more spokes required?

    I'm inclined to be a little conservative as control issues related to wheel stiffness are likely to be exacerbated by the cyclocross inspired geometry of this frame.

    Bri

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