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Where's the proof DB spokes more durable?

Old 08-04-19, 08:45 AM
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Originally Posted by AnkleWork
Fatigue life and modulus of elasticity are rather more important than UTS.
The ultimate tensile strength is a good indicator of fatigue life and elasticity. Fatigue life is difficult to measure and the modulus of elasticity can (and is) measured during the tensile strength test.
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Old 08-04-19, 08:57 AM
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Originally Posted by HillRider
This makes no sense. What you are saying is that less material is stronger. A 2 mm spoke has a cross section of 3.24 mm^2, a 1.8 mm spoke has a cross section of 2.54 mm^2. So the smaller cross section is stronger? Perhaps the tensile strength numbers are really given in kgf/mm^2 and the butted spokes are stronger per mm^2 due to cold working.
No. Less material isn’t “stronger”, it’s more elastic. If you look at the charts for the straight gauge spokes you can see that a 1.8mm spoke is breaks at lower force than a 2.0mm spoke, which is to be expected. But by thinning out the middle of the spoke, the spoke becomes more elastic and overall takes more force to break than a 2.0mm spoke. Add in a thicker head and it takes even more to break that head with a thin middle section that stretches.
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Old 08-04-19, 10:10 AM
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Originally Posted by shelbyfv
Well, this doesn't seem to be turning out much different from OP's similar spoke queries in past years. Not really surprising, but I guess you never know....
Originally Posted by Rodney King
Why can't we all just get along ?
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Old 08-04-19, 10:25 AM
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Originally Posted by cyccommute
Let’s start with tensile strength. The tensile strength being measured isn’t the wheel but the resistance of the spoke to breakage. Tensile strength measurements of the spoke gives you insight into how much it takes to fatigue the spoke to the point where it will break. Higher tensile strength (or resistance to breakage) will result in a strong, more durable wheel.

Pillar spokes is about the only place where I’ve seen actual measurements of tensile strength of various types of spokes. You have to look at multiple graphs to see what effect butting has on strength but it’s pretty clear when you compare them. For example a 2.0mm (14ga) spoke breaks at 270 kgf (kilograms force which is a really dumb unit). A 2.0/1.8/2.0mm breaks at 290 kgf (about) and a 2.2/1.8/2.0mm spoke breaks at about 330 kgf. They have a 2.3/1.8/2.0mm triple butted spoke that breaks at about 420 kgf. For comparison, their 2.3mm straight spoke breaks at about 360 kgf.

Their charts show pretty conclusively that butting the spokes increases their strength.
I'm pretty sure Jobst Brandt put data on spoke tensile strength into his book, The Bicycle Wheel. When I read it I was in engineering school and it seemed like the results of conventional technical measurements I was learning about. But since I graduated as an EE rather than an ME, you should probably just take this as a suggestion rather than a statement.

Brandt's overall conclusion was that spokes break because of excessive cycling into inelastic deformation. A thick spoke has a stiffer shaft which elongates less with an increase in tension, compared to a more noodly thin spoke shaft. If strain is common between the thick and thin spokes, then more strain occurs at the nipple and the elbow of a thick spoke, than with a thin spoke. The accumulation of fatigue damage should be faster for a thick-spoke wheel than for a thin-spoke wheel. At least this how I understand Jobst. But again, this is just a suggestion.
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Old 08-04-19, 10:28 AM
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Originally Posted by terrymorse
It lets you clamp onto the spoke to keep it from twisting.



Twist-resist Tool
That's what I needed - not "what is it for?" but "what's an example?" Sorry for being vague and thanks for guessing right! It looks like Park?
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Old 08-04-19, 10:34 AM
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Originally Posted by Brocephus
I get the physics argument for DB spokes over straight gauge, but what I'm wondering is if the difference is negligible, or if it's significant and tangible?
These days, my bikes get very low-stress use, just steady paced exercise, on good roads. No off-road, big-air thrashing, and no more road racing with heavy training, interval sprints, etc.
All my wheels are currently straight gauge Swiss DT's. Would I expect to get measurably longer service with DB spokes, or is this basically just an academic/technical argument, at least in my case?
I would think it's significant. Elasticity of a spoke is like that of a frame tube, where an increase in OD has a lot of leverage in the equation for stiffness. For frame tubes the stiffness increases with the square of the OD. If the diameter increases by 10%, the stiffness increases by 1.1*1.1 = 1.21 = 21%!
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Old 08-04-19, 10:47 AM
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Originally Posted by Road Fan
It looks like Park?
Not Park Tool. I think they [twist-resist tools] were made by Competition Cycles Services by modifying a fourth hand brake cable tool.

Sadly, I gave mine away years ago when I stopped building wheels.

See the comments on this amazon page.
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Old 08-04-19, 10:52 AM
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Originally Posted by Road Fan
Elasticity of a spoke is like that of a frame tube, where an increase in OD has a lot of leverage in the equation for stiffness. For frame tubes the stiffness increases with the square of the OD. If the diameter increases by 10%, the stiffness increases by 1.1*1.1 = 1.21 = 21%!
That's frame tube stiffness against bending. The only significant spoke stiffness is against elongation, which is a simple linear function of cross-sectional area.
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Old 08-04-19, 11:58 AM
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The problem with carbon fiber for spokes in a conventional wheel is that it's too rigid.

A current effort at fiber spokes is Berd, using Dyneema cord, that's been bury spliced at the hub end, and spliced onto a short length of spoke at the wheel end, and treated for abrasion resistance. There was a neato thread (haha) on MTBR about trying to recreate them hobby style, but Berd sent the ringleader a "please stop" message.
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Old 08-04-19, 12:42 PM
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Originally Posted by cyccommute
Let’s start with tensile strength. The tensile strength being measured isn’t the wheel but the resistance of the spoke to breakage. Tensile strength measurements of the spoke gives you insight into how much it takes to fatigue the spoke to the point where it will break. Higher tensile strength (or resistance to breakage) will result in a strong, more durable wheel.

Pillar spokes is about the only place where I’ve seen actual measurements of tensile strength of various types of spokes. You have to look at multiple graphs to see what effect butting has on strength but it’s pretty clear when you compare them. For example a 2.0mm (14ga) spoke breaks at 270 kgf (kilograms force which is a really dumb unit). A 2.0/1.8/2.0mm breaks at 290 kgf (about) and a 2.2/1.8/2.0mm spoke breaks at about 330 kgf. They have a 2.3/1.8/2.0mm triple butted spoke that breaks at about 420 kgf. For comparison, their 2.3mm straight spoke breaks at about 360 kgf.

Their charts show pretty conclusively that butting the spokes increases their strength.
Originally Posted by cyccommute
The ultimate tensile strength is a good indicator of fatigue life and elasticity. Fatigue life is difficult to measure and the modulus of elasticity can (and is) measured during the tensile strength test.
Does anybody care about the tensile strength of a spoke at breaking? It's the usual shuck and jive attempt to cover up erroneous pontifications. Modulus of elasticity, yield strength, and fatigue life are independent of breaking strength and are investigated, specified and published for structural metals and each is used to inform the design process. Your “breakage” force is only meaningful at catastrophic failure for determining safety factors.

Clue: Fatigue life, yield strength, and modulus of elasticity are all measured independently of ultimate tensile strength at breakage. Keep going down your rabbit hole and you’ll soon post something like “Tighten the nipple until the spoke breaks then back off x turns.” HAW!

Last edited by AnkleWork; 08-04-19 at 02:03 PM.
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Old 08-04-19, 02:25 PM
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Originally Posted by terrymorse
That's frame tube stiffness against bending. The only significant spoke stiffness is against elongation, which is a simple linear function of cross-sectional area.
It's not also based on moment of inertia?
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Old 08-04-19, 02:27 PM
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Originally Posted by terrymorse
That's frame tube stiffness against bending. The only significant spoke stiffness is against elongation, which is a simple linear function of cross-sectional area.
Well, maybe so! Sorry, all!
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Old 08-04-19, 03:40 PM
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Originally Posted by Road Fan
It's not also based on moment of inertia?
Moment of inertia is only relevant for bending and twisting (torsion), not elongation (strain).

ε (strain) = σ (stress) / E (Young's modulus)

If you double the cross sectional area, you half the stress, and thus the strain.
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Old 08-04-19, 07:17 PM
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Originally Posted by AnkleWork
Does anybody care about the tensile strength of a spoke at breaking? It's the usual shuck and jive attempt to cover up erroneous pontifications. Modulus of elasticity, yield strength, and fatigue life are independent of breaking strength and are investigated, specified and published for structural metals and each is used to inform the design process. Your “breakage” force is only meaningful at catastrophic failure for determining safety factors.
Perhaps you should look up the definitions of elastic modulus, yield strength, and metal fatigue. While you are at it you you might want to look at breaking strength. All are related to the effect of stress and strain on metals. You get the elastic modulus from the slope of the stress and strain curve below the yield point which you get off the same curve. Rupture, or “breakage” occurs on the same curve post the ultimate strength point.

If you can get them all off the same curve...like those presented by Pilar Spokes...they are related by definition.



Clue: Fatigue life, yield strength, and modulus of elasticity are all measured independently of ultimate tensile strength at breakage.
No, they aren’t. They are all measured on the same equipment and in the same test. Look it up.

Keep going down your rabbit hole and you’ll soon post something like “Tighten the nipple until the spoke breaks then back off x turns.” HAW!
Non sequitur much?
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Old 08-04-19, 07:56 PM
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.
...if a spoke breaks in the forest, and there's no one around to hear it, does it still make a sound ?
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Old 08-04-19, 08:05 PM
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Micro examination of spoke failure always shows the same thing. We know why and where spokes fail but cannot answer the “when.” The measure of science is not hindsight ability to explain but predictive power. By this standard, the science of spoke failure is as weak as most macroeconomics.

If breakage is wire material based, then consistency with adequate strength, is paramount. You bet. Wire consistency is an obsession of spoke makers and they have as little control as you once they accept the wire. There are too many variables over too many miles of wire. Variables include annealed state, surface finish, micro-hardness variability, occlusions and contaminants, crystal structure uniformity, and more.

Making strong wire (high tensile strength) is straight forward. Making it über consistent is very hard. Stainless wire for high end spokes is so extreme and unique in this parameter that it sees no other industrial use. No one would pay so much for consistency outside of medicine and there aren’t many medical uses for 14g wire.
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Old 08-05-19, 12:29 AM
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Originally Posted by cyccommute
No, they aren’t. They are all measured on the same equipment and in the same test. Look it up.
I work in a field where we use some of these machines and the ones for fatigue are different. The frequency and amplitude that they pull is dictated by the test, and they need an actuator and control system to do that. A test for modulus and yield is much simpler. It just pulls with increasing force and measures the strain. There are other types too. We make rubber stuff and the strain rate is important for us because it's viscoelastic. Our machines are Instron brand.
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Old 08-05-19, 01:09 AM
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Originally Posted by cyccommute
by thinning out the middle of the spoke, the spoke becomes more elastic and overall takes more force to break than a 2.0mm spoke.
If I grab a DB spoke, pull on both ends, it will break at a higher tension than a straight-gauge spoke?

If the spokes are more elastic, doesn't the rim deform more, thus break sooner?
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Old 08-05-19, 07:49 AM
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Originally Posted by Darth Lefty
I work in a field where we use some of these machines and the ones for fatigue are different. The frequency and amplitude that they pull is dictated by the test, and they need an actuator and control system to do that. A test for modulus and yield is much simpler. It just pulls with increasing force and measures the strain. There are other types too. We make rubber stuff and the strain rate is important for us because it's viscoelastic. Our machines are Instron brand.
Yes, measuring fatigue is a different test. My mistake. But elasticity, yield and ultimate tensile strength for spokes are all measured on the same instrument at the same time. You get them of the same graph.
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Old 08-05-19, 07:59 AM
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Originally Posted by Arthur P*****y
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
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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Old 08-05-19, 08:31 AM
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Originally Posted by terrymorse
Moment of inertia is only relevant for bending and twisting (torsion), not elongation (strain).

ε (strain) = σ (stress) / E (Young's modulus)

If you double the cross sectional area, you half the stress, and thus the strain.
Hi, thanks for the reminder!
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Old 08-05-19, 05:02 PM
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Shelbyfv, I have posted a few times on this subject and have yet received an answer. What brought it up this time was a discussion with the service manager at the shop where I work weekends. He insists DB spokes are more durable and resist breaking better than straight gauge. I asked him for proof, which of course he did not have. I suppose this has to be laid to rest, and I will have to simply turn the other cheek when I hear the proclamation of the virtues of DB spokes.
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Old 08-05-19, 05:14 PM
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Originally Posted by TiHabanero
Shelbyfv, I have posted a few times on this subject and have yet received an answer. What brought it up this time was a discussion with the service manager at the shop where I work weekends. He insists DB spokes are more durable and resist breaking better than straight gauge. I asked him for proof, which of course he did not have. I suppose this has to be laid to rest, and I will have to simply turn the other cheek when I hear the proclamation of the virtues of DB spokes.
Ya pays yer money, and ya takes yer chances. That's the beauty of having a variety of different products on the market.

I suspect there are a lot of choices in bike design that are not backed up by detailed analysis or testing. There aren't enough bikes in the world to test every possible configuration and riding condition to destruction with enough data for good statistics. As a result, we're often faced with gathering the best advice that we can get, and making our own choices. Best of luck!
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Old 08-05-19, 06:56 PM
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Originally Posted by TiHabanero
I suppose this has to be laid to rest, and I will have to simply turn the other cheek when I hear the proclamation of the virtues of DB spokes.
This sounds like a rational plan if the idea still bothers you. On the other hand, there seems to be no "proof" that DB spokes are less durable. Frankly, I lack the educational accomplishment to evaluate any such proof absent someone to interpret it for me. I'm confident DT, Mavic and the other manufacturers have employees who are familiar with whatever data exists and are able to use it to the benefit of their products. They have much more "skin in the game" than any of us. Durability may be only one of a number of qualities, but clearly they have decided that DB spokes are appropriate in better wheels.
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Old 08-05-19, 07:56 PM
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Originally Posted by TiHabanero
Shelbyfv, I have posted a few times on this subject and have yet received an answer. What brought it up this time was a discussion with the service manager at the shop where I work weekends. He insists DB spokes are more durable and resist breaking better than straight gauge. I asked him for proof, which of course he did not have. I suppose this has to be laid to rest, and I will have to simply turn the other cheek when I hear the proclamation of the virtues of DB spokes.
I think a lot of these discussions go into the weeds because the benefits aren't stated accurately. A 2.34mm straight-gauge spoke by itself is obviously way stronger than a DT Revolution. The spoke strength chart at the back of Jobst's bike actually shows that straight-gauge spokes can be pulled to somewhat higher tensions than butted spokes of the same end thicknesses.

But with bikes, we like to optimize things. Straight-gauge spokes tend to break (if/when they do) at the ends, meaning that there's more material in the center than necessary; the ends are the weak links. So it's logical to think that if you put extra material on the ends and took it away from the middle in just the right amount, you'd end up with a spoke that is equally durable from end to end. From there, you'd scale the whole thing up or down according to your needs. (My rando bike wheelset is an experiment in scaling down -- 4300 miles so far on 32/3x 1.8/1.6/1.8 and I'm wondering if I could have pushed it further!)

Given the question of how straight-gauge spokes don't seem to break a lot more even though they are more likely dip to zero tension at the bottom or when hitting potholes, I think the extra material compensates to some degree. Plus (per Jobst), spokes carry load in proportion to their tension, so I think that's another way that life isn't as hard for NDS spokes as one would imagine.

So if the extra weight of straight-gauge spokes doesn't bother you or cause problems, the world is your oyster. They're cheaper and easier to build into wheels. People ride many thousands of happy miles on straight-gauge spokes without being aware of it.
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