My understanding is that more material in middle of spoke equals more leverage hence flex? Butted (bladed) spokes equals less (different) material for force to be transferred with, hence less flex? Or crazy to attribute stiffness to one part of spoke metric?

Thickness matters most at the ends as less/different spoke material at middle doesn't equal flex and that style of build... tension, spoke placement, rim design systemically creates stiffness. Oui?

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Only if it has a high margin of utility.

No.

Under normal circumstances (in a proper wheel build) a spoke only works in tension. The spokes always have some tension in them like the strings of a guitar. The more material there is, the more the spoke will resist stretching. This resistance to stretching is what makes a wheel stiff laterally.

So long as the cross-sectional area is the same, the shape of the spoke isn't a factor. What that means is whether the spoke is round or it's oval or bladed, the amount of material is the determining factor. If the DT Aero Comp is forged from a DT Competition, it will behave like one (except with regards to aerodynamics).

Spokes are butted so the stresses are absorbed by the section with less material which is straight along the middle section (more willing to stretch). The ends are thicker and have to be forged into threads and elbow (or mushroom tip for straight pull spokes). By having the length of the spoke take up the stresses of riding, the ends are less prone to failure.

-Eric

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I don't agree with you Ergott. Second moment of inertia is the key to figure out how a component behaves under a load, be they under tension or not.
Although I believe in this theory, I will test it on the bench to clear things up.

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Could you elaborate on what you mean by second moment of inertia?

I'd love to know more about your test when you do it. What order of magnitude do you think the differences in stiffness be? How will you rule out other factors?

Please keep me posted to what you find out. I really appreciate the work you do.

-Eric

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I tend to side with Adrien on this one on gut feel and thinking about how much easier it is to bend something that is thinner versus thicker. But I find the discussion interesting. Truth is, if the DT Comps are in fact laterally more stable I would go with those (for me, at 195lbs) and say phooey to any aero benefit that might be obtained by flattening them a bit. I'll look forward to your guys' ultimate conclusions on this one.

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My Special Colnago EPQ

I don't understand what you're trying to say

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Clear up your quotes. Looks like you are quoting me.

-Eric

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I don't know if Second Moment of Area has much to do with tension. It is basially a value of the amount of material and how far it is from a central axis.
It is very important in bending, torsion and buckling, but not in pure tension. Hookes Law does't account for Second Moment of Area.

Its likely that the different forging processes have a more significant effect to the material properties than the shape would, in tension.

This is my point. Basically a rim lateral load involves a deflection of the rim, thus a bending of the spokes near this load. The thickness of the spokes is what directly resists to this bending. The width of the spoke also enters into the equation, but with a less important factor.
That is why I'm sure the round 1.8mm DT Competition is laterally stiffer than the new DT Aero Comp 2.3/1.2.
An easy application: take an Aerolite spoke and a Revolution spoke in hand. Bend the Aerolite along its thin section. Now bend a Revolution (1.5mm round). You will see that it resists more to bending.
When the wheel is under tension, the spokes exactly behaves in the same manner in my opinion. Why wouldn't they?
Anyway, I get your and Ergott's points to say that the tensile strength of the spoke is the same whatever the shape of the spoke. In this case, the amount of material is what matters.



Another important point is the twisting of the spoke while tensionning it. A DT Aero Comp is flatten so it can be hold well during tensionning.
A DT Competition is round so it can't be hold against twisting. You need a good wheelbuilder for reaching high spokes tensions with a round spoke.
Although round spokes were very common in the past for custom wheels, the new options offered with bladed spokes and how easy they are to build into a durable wheel, have made them a premium choice for most wheels.



Second moment of inertia: above in my post.
For the test, I will take a rim, a hub, and DT Competition spokes. I will build properly the wheel with a given lacing pattern (certainly radial) until it has good and measured spokes tension. I'll disassemble it, then build it again with the new Aero Comp, same pattern, same spoke tension. The rim will be exactly the same, and the lateral load will be applied at the very same spot on the rim.

Cheers,
Adrien.

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But when a properly tensioned wheel is loaded the spoke has to elongate before it can bent (a tiny bit). Bending a spoke requires little force, although it is harder to bent a Revolution spoke than an Aerolite there is little force required to bent the spoke. However to elongate the spoke a much larger force is required.

I partly agree with Ergott. Deflection (stretching/elongation in this case) for a subejct that are under tension are only influenced the cross sectional area but also the modulus of elasticity. We know the cross section but don't know the exactly modulus of elasticity. What we do know is that the material used for CX-Ray, Laser and Race has different yield strenght. CX-Ray is made the the highest quality / strongest material. Some might imply that they could have different modulus of elasticity, but you can't conclude this from the strenght of the material. This is just a question which we don't the answer on.

This also means I don't agree with Arien. Like milroy also implies second moment of area and second moment of inertia only come in to play when we are taking about bending. Adrien gives the perfect exampel on this. When you try to ben a flat spoke it will deflect much more around on axis compared to the other axis. A round spoke have the same second moment of inertia around both axis. It will deflect less around one axis and more around the other axis compared to a flat/bladed spoke. But a spoke is not exposed to bending forces!

The second moment of inertia also has something to say for a members under compression - like a column. But I my mind a tensioned spoke in a wheel will never be under compression.

Just my to cents. I'm not a wheelbuilder - just a structural engineer working with bending, tension and compression everyday in and out.

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My Simplon Pavo II

Thank you for your different point of view.
I will perform the test over the week-end so we will know what exactly happens to the wheel stiffness.

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Wow, that's great. Thanks. One question though, you mention you'd lace up the wheel with the same tension on both trials. Wouldn't the aero comp inherently be tensioned higher than the regular comp for any given wheel, all else being equal? I guess what I'm wondering is if the test would be best if done with the optimal spoke tension for that particular spoke and wheel combo, not necessarily the same tension, since as you mentioned, flattened spokes can often be built using higher tensions. Just smack me if I'm off base here. I don't know.

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My Special Colnago EPQ

The CX-Ray is literally a Laser that they forge into a blade. The same stainless steel is used.

-Eric

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Last question. If the bending of the spoke is near the load, wouldn't the results be the same? All the spokes in question have round, 2mm ends.

I'm eagerly waiting the results. Thanks for doing this.

-Eric

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