effect of spoke type on wheel stiffness

[nmrt]

i have a wheelset with some pillar megalite spokes. the spokes are very light at 3.8 g per spoke.
now, if i change these spokes to a dt aerolite (4.3 g) or a CXray (4.3 g), all else being the same, would my wheel feel stiffer?

Btw, the wheel setup in 20 spoke front and 24 back. tune hubs laced to kinlin xr270 rims.

[Marin]

It would be stiffer, but I don't know if you would feel it.

[NiFTY]

I would think probably not, it is the tension the spoke is under that supplies the stiffness rather than each spoke having any intrinsic stiffness.

[Mario Jr.]

I would think probably not, it is the tension the spoke is under that supplies the stiffness rather than each spoke having any intrinsic stiffness.

Eh, no. If the spokes has a basic tension, the wheel will NOT get any stiffer by increasing the tension. The spoke angle and the amount of material in the spokes are what decides the stiffness.

So yes, your wheel will get a little stiffer by replacing the spokes for thicker ones.

[Calnago]

Agree with @Mario Jr and would go one step further and say the cross section of the spoke also plays into it. A round spoke would build a laterally stiffer wheel than an equivalent (same amount of material) flat (aero) spoke.


Sent from my iPhone using Tapatalk

[ergott]

Let's clear a few things up here. These are basic properties of materials, not speculation.

1) Wheels stiffness isn't dependent on spoke tension. If there is tension (no spokes doing slack), there is no significant change in wheel stiffness by increasing tension. Tension is increased to lessen the chance of spokes going slack.

2) Spoke shape doesn't matter. It's the cross-sectional area of the spoke that does. The cross-sectional area of a Sapim Laser and a Sapim CX-Ray is the same. Sapim takes a Laser spoke and forges it into the oval shape of a CX-Ray. Since the area is the same, the stiffness of the wheel is the same. Remember the force acted on spokes is along their length. All spokes do is resist the efforts of the rim and hub pulling on them.

OP, I think the difference is small comparing the spokes in question. If you are concerned with the stiffness of your wheels I would start with replacing the rear wheel spokes on the drive side with a heavier gauge spoke like the DT Competition or Sapim Race. That part of the wheel has the worst bracing angle between the hub and rim because the cassette is in the way. Ideally you want the spokes pulling on the rim for the largest bracing angle. Imagine trying to hold up a tree with a rope. You don't want to stand next to the tree to do this, you want to step back as far as you can so you have more leverage. When you can't do that you want a thicker, stronger rope assuming you are strong enough to still hold the tree from where you are standing.

[WMW]

+1 Eric.

Except increasing the size of the DS spokes alone won't increase lateral stiffness much. Most stiffness comes from the NDS because its bracing angle is so much higher. Lateral spoke stiffness goes up with the square of the bracing angle. Heavier DS spokes *will* increase the loads the rear wheel can take before the NDS spokes go slack though.

OP... f you want a rear wheel optimized for stiff and light, then step one is to get a hub that not only has a stiff internal structure, but also has the maximum possible DS offset (hitting your derailleur on the spokes in the limiting factor), and a NDS offset that is ~2.2x that. And use heavier DS spokes (like DT Aero Comps) and super light ones on the NDS. Most hubs aren't designed for that though and have a ratio of ~2x, so it's probably best to just use the same gauge on both sides. The spoke stiffness is proportional to the cross section of the spoke if we are comparing stainless steel, so you will see an improvement in lateral stiffness with heavier spokes, but frankly I wouldn't do it unless there is some other reason... like you were breaking spokes or something.

[Calnago]

Let's clear a few things up here. These are basic properties of materials, not speculation.

1) Wheels stiffness isn't dependent on spoke tension. If there is tension (no spokes doing slack), there is no significant change in wheel stiffness by increasing tension. Tension is increased to lessen the chance of spokes going slack.

2) Spoke shape doesn't matter. It's the cross-sectional area of the spoke that does. The cross-sectional area of a Sapim Laser and a Sapim CX-Ray is the same. Sapim takes a Laser spoke and forges it into the oval shape of a CX-Ray. Since the area is the same, the stiffness of the wheel is the same. Remember the force acted on spokes is along their length. All spokes do is resist the efforts of the rim and hub pulling on them.

OP, I think the difference is small comparing the spokes in question. If you are concerned with the stiffness of your wheels I would start with replacing the rear wheel spokes on the drive side with a heavier gauge spoke like the DT Competition or Sapim Race. That part of the wheel has the worst bracing angle between the hub and rim because the cassette is in the way. Ideally you want the spokes pulling on the rim for the largest bracing angle. Imagine trying to hold up a tree with a rope. You don't want to stand next to the tree to do this, you want to step back as far as you can so you have more leverage. When you can't do that you want a thicker, stronger rope assuming you are strong enough to still hold the tree from where you are standing.

Hi @Eric, with regard to your point 2) above, I think there may be something incorrect there, or maybe I'm missing something? Cross sectional area is really dependent on an angle of view. For instance, the cross sectional area looking at a the "fat" side of a bladed spoke is much larger than the cross sectional area of the same flat spoke looking at it from it's "skiinny" blade point of view. No? And the directional strength of something certainly can be affected by shape. Anyway, I don't build nearly the number of wheels you do, and maybe we're way off a non relevant theoretical tangent, but I do believe all else being equal, a wheel built with Lasers will be laterally stiffer than one built with CX Rays. I generally use the equivalent DT Swiss versions, but the principle is the same. And when one is in a sprint and bike and wheels are being wrenched side to side, there are indeed some lateral forces at play in addition to just the tension between hub and rim via the spoke, no?

I always like to use easy to understand examples of stuff to demonstrate a point. Take a round pipe. Try to bend it. Maybe you can, maybe you can't, dependis on how strong and thick it is to begin with. Now squash that same pipe till it's flat and wide. Can you bend it now? If you can, it is much easier to bend pushing on the flat wide side than from pushing on one of it's now thin edges. Same as a saw blade. Wobbles back and forth from side to side when you wave it in the air, yet it is strong enough to cut vertically to support itself while cutting through the tree, with the sides of the tree as you cut keeping the blade from bending.

[DMF]

Remember that there have been plenty stiff wheels with completely soft spokes, like the Spinergy PBO bendable fiber spokes. These even made for excellent downhill mtb wheels where lateral stiffness really comes into play.

[ergott]

I always like to use easy to understand examples of stuff to demonstrate a point. Take a round pipe. Try to bend it. Maybe you can, maybe you can't, dependis on how strong and thick it is to begin with. Now squash that same pipe till it's flat and wide. Can you bend it now? If you can, it is much easier to bend pushing on the flat wide side than from pushing on one of it's now thin edges. Same as a saw blade. Wobbles back and forth from side to side when you wave it in the air, yet it is strong enough to cut vertically to support itself while cutting through the tree, with the sides of the tree as you cut keeping the blade from bending.

Take that example and pull on the pipe instead of trying to bend it. If the pipe is oval or a circle it doesn't matter. You aren't trying to bend the spokes you pull on them.

Cross sectional area is when you slice the material 90deg from it's length. If you take the area of a DT Aerolite and a DT Revolution it will be the same. For that matter if you were to weigh the two (providing they are the same length) they will weigh the same as well. You are dealing with the same amount of material that is resisting being pulled apart. Since the material used is the same, the properties of stiffness will be the same.

Hope that helps.

[ergott]

+1 Eric.
Most stiffness comes from the NDS because its bracing angle is so much higher.

I agree. I just don't recommend it without knowing more about the hub as you already understand. If the resulting tension ratio leaves the nondrive spokes at a tension that is too low, a stiffer spoke is more likely to go slack. Durability then suffers. DT 240 is a good example of a hub that works well when both sides of the rear wheel use stiffer spokes. The older White Industries hubs (H3 Campagnolo and first run of T11s) are examples of hubs that benefit from lighter gauge spokes on the nondrive side. Another circumstance where it can be an issue is with rims that can't handle higher tensions. That in combination with a hub that has a left flange resulting in less than 50% of the right side tension makes for the condition where heavier gauge spokes are likely to go slack on the left side.

[Calnago]

I always like to use easy to understand examples of stuff to demonstrate a point. Take a round pipe. Try to bend it. Maybe you can, maybe you can't, dependis on how strong and thick it is to begin with. Now squash that same pipe till it's flat and wide. Can you bend it now? If you can, it is much easier to bend pushing on the flat wide side than from pushing on one of it's now thin edges. Same as a saw blade. Wobbles back and forth from side to side when you wave it in the air, yet it is strong enough to cut vertically to support itself while cutting through the tree, with the sides of the tree as you cut keeping the blade from bending.

Take that example and pull on the pipe instead of trying to bend it. If the pipe is oval or a circle it doesn't matter. You aren't trying to bend the spokes you pull on them.

Cross sectional area is when you slice the material 90deg from it's length. If you take the area of a DT Aerolite and a DT Revolution it will be the same. For that matter if you were to weigh the two (providing they are the same length) they will weigh the same as well. You are dealing with the same amount of material that is resisting being pulled apart. Since the material used is the same, the properties of stiffness will be the same.

Hope that helps.

Yes, I get that... pulling end to end is the same, and at a 90 degree cross section, the cross sectional area is the same as well. But cross sectional area cannot be talked about without talking about the angle which it is being derived from, that angle is an integral part of what defines "cross sectional area", right? We're probably getting into uber nerd territory now, but the concept is interesting. So, even though pulling the spoke end to end is the same whether a Revolution or an Aerolite is in question, the aerolite would sway a lot more in one direction than the other if your were to wave it about, whereas the revolution would sway the same no matter what angle it was being swayed from. In a perfect world with no lateral forces, then no issues. In fact, the aerolite would be better simply due to it's aerodynamic properties in the plane it's travelling. But when you start swaying the bike from side to side lateral forces come into play (or do they?), and the round spokes are thicker in that directional plane. At least, that's how I look at it. I may be wrong here, because I do see where you're coming from as well, that there are only pulling forces on the spoke involved, all else being equal. But I have to say, wheels I ride built with round spokes just seem more solid to me than wheels built with aero spokes. Maybe if I get a chance I'll build some identical wheels except for the spokes and try it out sometime as my own little experiment.

Thanks, interesting discussion and sorry I've kinda forgotten what the OP's original question even was, but I'm sure he's quite bored with it now...

[ergott]

But when you start swaying the bike from side to side lateral forces come into play (or do they?),

When you put lateral force on a wheel it pulls on the spokes more. It doesn't try to bend them. Spokes could be made out of string and have no resistance to bending. They would still work the same. In fact, that's the idea behind Lightweight wheels. The carbon fiber they use for spokes isn't strong with regards to bending them at all. The are super strong in the plane intended which is to resist the ends that are pulling on them (rim and hub). If you were to take a Lightweight spoke be itself and try to bend it, you easily can.

Imagine wind starting to blow the tree you are holding up with rope. The rope doesn't want to bend, it is pulled on harder.

[Calnago]

Yes, I see your point which is why I questioned myself with the "(or do they?)" in my thoughts above. It's a debate I've had with myself sometimes. Good to hear it talked through. Thanks.

Now... hope the OP got his answer long ago. Sorry for the diversion.

[WMW]

But cross sectional area cannot be talked about without talking about the angle which it is being derived from, that angle is an integral part of what defines "cross sectional area", right?

The mistake you are making is that the spokes have very little bending stiffness compared to their axial stiffness... plus they are usually not fixed at the ends... they pivot. Crossed spokes will have resistance to pivoting at the hub, but it is still going to be a trivial factor because of the lack of bending stiffness.