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Real World Test Data on Double Butted Spokes?
One hears it all the time, and the experts proclaim it, however I have not been able to find any studies that demonstrate the superior fatigue resistance to breakage of double butted spokes. Please, does anyone have access to any real world testing of double butted spokes vs. straight gauge spokes when laced into a wheel?
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Still chewing on this, eh?:foo: https://www.bikeforums.net/bicycle-m...ed-spokes.html
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What is 'real world' + 'data'. In all my years in R&D darned if we could ever equate the two because the real world is just so complicated, see above.
I suppose it is just more fashionable words, like the 'research on the internet' everyone seems to engage in these days... ;) |
I think the argument in favor of DB spokes is theoretical, and it makes sense to me. However, I suspect that the advantages of DB spokes are small when compared to differences in rim strength, hub flange design, and the overall quality (tension, evenness of tension) in a wheel build. I also suspect that straight gauge spokes have a bad rap, in part, because they are more commonly used in lower quality machine-built wheels which will fail more often for reasons.
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It's been several years but we had an amusing poster, arm chair engineer type, who went on at length about his efforts to convince some large company (DT Swiss?) that straight gauge spokes were better for bikes. IIRC, he had also tried to foist his "discovery" on some known wheel authorities (Brandt?) w/o success. I wish I could remember the user name, was quite entertaining.:beer:
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I was just trying to figure out how you could do a real world, scientifically defensible, test. It's tough, because even if I weighed the same as my neighbor (the scrawny lightweight) and we used similar wheels, we ride different routes, over different roads, etc.
This is the only way I could think of doing the test: 1. Build a wheel with half straight spokes, half butted. (Rear would probably be better, that's where most of my broken spokes come from.) 2. True and tension all the spokes on either side to the same tension. (Low end tension is likely to drive failure faster.) 3. Periodically touch up tension to make sure spokes aren't coming loose. 4. Ride lots and note which spokes fail. (This is likely to take a few years!) 5. Give me some credit when you publish the scientific paper that results from all this work. ;) |
This is an archive of a lot of Jobst Brandt's usenet debates. I don't see any place where he lays out directly why butted spokes (he refers to them as "swaged spokes") are better or worse, but he does address them in a couple of posts here and here. At various points, he seems to say that swaged spokes are better than straight-gauge spokes, but he also seems to be saying (and I hate to put words in his mouth) that spoke metallurgy has gotten so good that it doesn't matter.
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...the latest thing (that I've read) from the Wheel Fanatyk blog is all about cross sectional area in the spoke elbow. How more area at the elbow should give a longer spoke life. Not sure it's based on anything other than the theoretical, though. |
The spoke itself isn't the only thing that does better butted. My experience is that rims built on butted spokes are less likely to crack at the spoke holes. I'd guess the same would be true of the hub flanges cracking but my sample size of broken hub flanges is much to small to draw conclusions.
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I was a helper in the shipyard and the bolts on the high pressure steam turbine case were double butted.
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Originally Posted by shelbyfv
(Post 22230725)
Still chewing on this, eh?:foo: https://www.bikeforums.net/bicycle-m...ed-spokes.html
Originally Posted by FBinNY
(Post 15786912)
One of the earliest makers and promoters of waged (double butted) spokes was the Torington Company of Connecticut.
Interestingly they promoted the concept, not as stronger or lighter, but less expensive. Understand that the typical steels used for spokes have a shear strength of about 80% the tensile strength. Likewise the thread pf a 2mm spoke has a root diameter of about 1.8mm. So operating under the theory that a chain is no stronger than it's weakest link, any material in the middle of a spoke beyond 80% of the elbow diameter, or the root of the thread (whichever is lower) is wasted material, and a 2/1.6/2.0mm spoke will be as strong as a 2mm plain gauge spoke. Torrington wasn't as concerned about weight per se, but better use of pricey high strength steels and was selling their butted spokes at the same or lower price than competitors plain spokes. The info above applies only to strength. However rigidity is a function of the average cross section, so butted spokes build a wheel with flex properties comparable to plain spokes of the thin section. Lastly is the issue of fatigue, where butted spokes shine. All things being equal, the thinner mid section of butted spokes take up more of the deflections, and so tend to prolong the fatigue life of the ends. So, no matter how you slice it, the fact that butted spokes are superior when we consider strength, weight & fatigue life is no myth. But fortunately all types of spokes are still available, so you don't have to accept this and can still buy whatever spoke you want. |
Originally Posted by adamrice
(Post 22230901)
This is an archive of a lot of Jobst Brandt's usenet debates. I don't see any place where he lays out directly why butted spokes (he refers to them as "swaged spokes") are better or worse, but he does address them in a couple of posts here and here. At various points, he seems to say that swaged spokes are better than straight-gauge spokes, but he also seems to be saying (and I hate to put words in his mouth) that spoke metallurgy has gotten so good that it doesn't matter.
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While I don’t doubt that butted spokes are better, it has been a moot point for me. In my lifetime my weight has varied by 70 lbs, thankfully I’m closer to the lower end these days, and I’ve ridden both straight and butted without a problem.
I can’t recall ever breaking a spoke, or cracking a rim, although I must admit that we have good roads where I live. But I have a mtb with straight gauge spokes and it is holding up fine. What I do find amusing is that when digging info from the archives, decades ago the 36 spoke wheel was the gold standard for strong wheels, unless you were loaded touring, or tandem, or both then it was 40, or even 48. John |
Originally Posted by TiHabanero
(Post 22230678)
One hears it all the time, and the experts proclaim it, however I have not been able to find any studies that demonstrate the superior fatigue resistance to breakage of double butted spokes. Please, does anyone have access to any real world testing of double butted spokes vs. straight gauge spokes when laced into a wheel?
I have screen captured some of their graphs in the past. Straight gauge https://live.staticflickr.com/908/27...0339e299_w.jpgImage 5-11-18 at 1.41 PM by Stuart Black, on Flickr Double butted https://live.staticflickr.com/948/27...938cbb7b_w.jpgImage 5-11-18 at 1.44 PM by Stuart Black, on Flickr Triple butted https://live.staticflickr.com/964/42...4ff9074a_w.jpgImage 5-11-18 at 1.43 PM by Stuart Black, on Flickr You can see a clear increase in strength with butting and with increased head diameter. Looking at the 2.0mm spoke, going to a 2.0/1.8/2.0mm (1415 on graph) there is an about a 10% increase in strength. Going to a 2.2/1.8/2.0 (2018 on graph), there is a 22% increase in strength over a straight spoke. Pillar makes a 2.4/1.8/2.0mm quad butted spoke that has a breaking strength of 340 kgf or 25% greater strength than single butted. |
Tensile strength of spokes is almost completely irrelevant. Most spokes that break break from fatigue, IME.
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Originally Posted by pdlamb
(Post 22233163)
Tensile strength of spokes is almost completely irrelevant. Most spokes that break break from fatigue, IME.
For a large number of steels, there is a direct correlation between tensile strength and fatigue strength; higher-tensile-strength steels have higher endurance limits. |
Every spoke I've broken was at the head or the nipple.That would be the butted section.
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Originally Posted by oldbobcat
(Post 22233562)
Every spoke I've broken was at the head or the nipple.That would be the butted section.
I personally like only butted because they're lighter and they don't ride as stiff. And I prefer higher 28 or 32 spoke counts so it's even more pronounced. For the minimal price increase it's worth it to me. The only spoke I ever recall snapping happened in the 90's. |
Originally Posted by cyccommute
(Post 22233261)
According to the ASM International Elements of Metallurgy and Engineering Alloys, 2008, they are related.
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Originally Posted by pdlamb
(Post 22233954)
Sure, but if you build the wheel correctly you won't have fatigue from the stress dropping too low, so the correlation between tensile strength and fatigue doesn't matter anyway. No fatigue, no breakage, no dependence on tensile strength.
Originally Posted by Drew Eckhardt
(Post 17509873)
For a given slackness tolerance tension needs are proportional to cross-sectional area.
IOW, a 1.8mm diameter spoke needs 81% of the tension on a 2.0mm spoke. If 60 kgf is OK at 2mm, 49 kgf is just as good at 1.8mm, 38 kgf at 1.6mm, and 34 kgf at 1.5mm. |
Originally Posted by Lazyass
(Post 22233678)
Look at DT Swiss. The Champion is 14 and the Competition is 14/15/14. They're the same diameter at the head and nipple and the Comp is butted down in the center. Because the center is thinner on the Comp it bends easier and takes stress off the larger ends.
I personally like only butted because they're lighter and they don't ride as stiff. And I prefer higher 28 or 32 spoke counts so it's even more pronounced. For the minimal price increase it's worth it to me. The only spoke I ever recall snapping happened in the 90's. |
Originally Posted by pdlamb
(Post 22233954)
Sure, but if you build the wheel correctly you won't have fatigue from the stress dropping too low, so the correlation between tensile strength and fatigue doesn't matter anyway. No fatigue, no breakage, no dependence on tensile strength.
Wheels that are “built correctly” include using a spoke that has a greater tensile strength so that it survives the cycle of tension/detension better. |
Originally Posted by cyccommute
(Post 22232466)
Pillar Spokes doesn’t present testing in a laced wheel but they appear to have measured the breaking strength of all of their various spokes. They likely used some version of a machine like an Instron tester. You have to click through all the spokes to see the data. Comparisons of the various strengths means flipping back and forth between several pages so it’s not the easiest to use but it’s the only real data I’ve ever found.
I have screen captured some of their graphs in the past. Straight gauge https://live.staticflickr.com/908/27...0339e299_w.jpgImage 5-11-18 at 1.41 PM by Stuart Black, on Flickr Double butted https://live.staticflickr.com/948/27...938cbb7b_w.jpgImage 5-11-18 at 1.44 PM by Stuart Black, on Flickr Triple butted https://live.staticflickr.com/964/42...4ff9074a_w.jpgImage 5-11-18 at 1.43 PM by Stuart Black, on Flickr You can see a clear increase in strength with butting and with increased head diameter. Looking at the 2.0mm spoke, going to a 2.0/1.8/2.0mm (1415 on graph) there is an about a 10% increase in strength. Going to a 2.2/1.8/2.0 (2018 on graph), there is a 22% increase in strength over a straight spoke. Pillar makes a 2.4/1.8/2.0mm quad butted spoke that has a breaking strength of 340 kgf or 25% greater strength than single butted. It's well-established that butted spokes are superior to straight-gauge in every way except cost. I don't see how this is even debatable. |
Originally Posted by hydrocarbon
(Post 22237795)
It's well-established that butted spokes are superior to straight-gauge in every way except cost. I don't see how this is even debatable.
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