Old 08-05-19, 07:59 AM
  #45  
cyccommute 
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Originally Posted by Arthur P*****y View Post
If I grab a DB spoke, pull on both ends, it will break at a higher tension than a straight-gauge spoke?
That's what the Pillar graphs say.



Originally Posted by Arthur P*****y View Post
If the spokes are more elastic, doesn't the rim deform more, thus break sooner?
Rather than rewrite it, here's what Sheldon Brown says on the subject

Double-butted spokes do more than save weight. The thick ends make them as strong in the highly-stressed areas as straight-gauge spokes of the same thickness, but the thinner middle sections make the spokes effectively more elastic, allowing them to stretch (temporarily) more than thicker spokes.

As a result, when the wheel is subjected to sharp localized stresses, the most heavily-stressed spokes can elongate enough to shift some of the stress to adjoining spokes. This is particularly desirable when the limiting factor is how much stress the rim can withstand without cracking around the spoke holes.
In that same article he has this to say about the thicker head on butted spokes

Single- and triple-butted spokes solve one of the great problems of wheel design: Since spokes use rolled, not cut threads, the outside diameter of the threads is larger than the base diameter of the spoke wire. Since the holes in the hub flanges must be large enough for the threads to fit through, the holes, in turn, are larger than the wire requires. This is undesirable, because a tight match between the spoke diameter at the elbow and the diameter of the flange hole is crucial to resisting fatigue-related breakage.
I've also found this to be true through using triple butted spokes. The tighter fit as well as the greater cross-sectional area make for a more durable wheel, especially when used in touring bikes carrying heavy loads (rider and luggage). Where breakage was common with single and double butted spokes, it became uncommon when I switched to triple butted spokes. My building technique isn't any different, just the spoke.
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