# strength: bladed vs round vs oval spokes



## beaker (Feb 2, 2005)

I am getting ready to build up a new set of wheels for my wife's bike to replace the heavy oem set. I was considering using bladed or oval spokes for the build, but was wondering about the strength of bladed or oval spokes vs a round (straight or butted) spoke. Does the blading/ovalizing act the same as butting, or does it make a spoke weaker? I had a line on some older Asahi 15ga. bladed spokes in the right length for the front, so I thought I might give it a try, but not if its going to be a much more fickle wheelset.

For reference, the build will be 28h f/r Sun Venus (old style) rims, ultegra hubs. Probably radial front, 2x rear. I have some experience in wheelbuilding (5 wheels from scratch and a couple re-tensions for a friend), but I don't think Wheelsmith is exactly knocking on my door.


----------



## Mark McM (Jun 18, 2005)

*Butted, swaging and flattening*



beaker said:


> I am getting ready to build up a new set of wheels for my wife's bike to replace the heavy oem set. I was considering using bladed or oval spokes for the build, but was wondering about the strength of bladed or oval spokes vs a round (straight or butted) spoke. Does the blading/ovalizing act the same as butting, or does it make a spoke weaker? I had a line on some older Asahi 15ga. bladed spokes in the right length for the front, so I thought I might give it a try, but not if its going to be a much more fickle wheelset.


Basically, all spokes start as a straight wire, which is threaded at one end, and formed as a head (with or without elbow bend) at the other. Butted, bladed or ovalized spokes have an additional step that their center sections are "squeezed" down into a smaller cross section. This "squeezing" can either be done by rolling (forcing the wire through a small gap between roller) or forging (basically hammering them into shape).

In terms of spoke durability, the important thing to remember is that the ends of the spoke, whether straight, butted, ovalized or bladed, are basically the same for all types of spokes - the differences are only in the middle section. The reason this is important is because spokes virtually never break in the middle - they break at the stress concentrations at the ends (either at the threads, the elbows, or sometimes the heads). So the shape of the middle of the spoke has little to do with its durability.

That being said, in addition to different aerodynamic qualitys, different spoke shapes do have different mechanical characteristics that may need to be taken into consideration. Firstly, spoke longitudinal stiffness is primarily determined by the cross-sectional area of the spoke. For example, a 3.2mm x 1mm bladed spoke has about the same cross-sectional area as a straight 2mm round spoke, so wheels with either spoke will have about the same stiffness. So too, a Wheelsmith AE15 spoke has about the same cross-sectional area as a 1.8/1.6/1.8 round spoke, and a Sapim CX-Ray has about the same cross-sectional area as a DT Revolution 2.0/1.5/2.0, and therefore the AE15 will have similar stiffness to a 1.8/1.6/1.8 spoke, and a CX-Ray will have similar stiffness to a Revolution spoke.

Another aspect to consider is that ovalized and bladed cross-sections have lower torsional stiffnesses and strengths than round cross-sections of the same area. That means that, for example, a WS AE15 will twist more than an 1.8/1.6/1.8 spoke when tightening the nipples, and are more likely to shear off under torsion when turning the spoke nipples. Of course, spokes are subject to torsional loads when the wheel is being ridden, so the torsional stiffness and strength only come into play when the wheel is being built or trued.

So basically, ovalized and bladed spokes are not only more expensive, but are more difficult to build with and more difficult to get up to high tension, and also more difficult to maintain. But in actual use, they are no less durable than round spokes.


----------



## winstonc (Nov 18, 2002)

beaker said:


> I am getting ready to build up a new set of wheels for my wife's bike to replace the heavy oem set. I was considering using bladed or oval spokes for the build, but was wondering about the strength of bladed or oval spokes vs a round (straight or butted) spoke. Does the blading/ovalizing act the same as butting, or does it make a spoke weaker? I had a line on some older Asahi 15ga. bladed spokes in the right length for the front, so I thought I might give it a try, but not if its going to be a much more fickle wheelset.
> 
> For reference, the build will be 28h f/r Sun Venus (old style) rims, ultegra hubs. Probably radial front, 2x rear. I have some experience in wheelbuilding (5 wheels from scratch and a couple re-tensions for a friend), but I don't think Wheelsmith is exactly knocking on my door.


Mark McM did a good job, but I'll put in my two cents. I believe the ovalizing process is a cold-working method, which doesn't affect spoke stiffness (stiffness depends on cross-sectional area), but it does make the spoke stronger. However, the extra strength doesn't really make a difference since breakage generally occurs at the bend, not in the middle of the spoke.

Bladed/oval spokes may be more prone to twisting, but there is an advantage: you can see when they're twisted, unlike round spokes, and you can use a padded pair of pliers to prevent twisting.


----------



## Mark McM (Jun 18, 2005)

*Careful there - material strength not the same as component strength*



winstonc said:


> I believe the ovalizing process is a cold-working method, which doesn't affect spoke stiffness (stiffness depends on cross-sectional area), but it does make the spoke stronger. However, the extra strength doesn't really make a difference since breakage generally occurs at the bend, not in the middle of the spoke.


Carefull there - cold-working may increase the material strength of the middle of a butted spoke, but that doesn't mean the actual spoke is stronger. Cold working increases the _strength per unit area_ of the material. But because the cross-sectional area is reduced, the final strength may actually be smaller. For example, the forged 1.5mm center section of a DT Revolution 2.0/1.5/2.0 has a material strength (strength per unit area) close to 20% greater than the material at the 2.0mm ends - but because the cross-sectional area has been reduced by 50%, the actual strength in the middle 1.5mm section is only about 60% of the strength of the 2.0mm ends.

But as mentioned before, the reduced strength in the middle is moot because spokes don't typically break in the middle, they break where stress-concentrations can initiate fatigue cracks, and the stress concentrations occur at the threads, elbow or head, not in the middle.


----------



## winstonc (Nov 18, 2002)

I meant to compare, say, a 1.5mm round spoke with one that starts off at the same diameter but is forged into an oval shape, like the Wheelsmith AE15. In this case, the final forging step changes the cross-sectional shape but not the area, and total strength should be increased.

Of course, if you're talking about a process that makes the spoke narrower, is more complicated.

I've read that good butted spokes are made so by forging rather than by drawing. I have a hard time picturing how this is done, though. Do you know how this is done?


----------



## Mark McM (Jun 18, 2005)

*AE15 cross-section area*



winstonc said:


> I meant to compare, say, a 1.5mm round spoke with one that starts off at the same diameter but is forged into an oval shape, like the Wheelsmith AE15. In this case, the final forging step changes the cross-sectional shape but not the area, and total strength should be increased.
> 
> Of course, if you're talking about a process that makes the spoke narrower, is more complicated.


Well, one of the big differences between "bladed" and "ovalized" spokes is that bladed spokes typically have the same cross-section area in the bladed section, whereas ovalized spokes have a reduced cross-sectional area. Consequently, bladed spokes are very wide (usually 3mm or more) and generaly require slotting to fit through the hub's spoke holes, whereas ovalized spokes are not much wider than standard spokes and are able to fit through standard round spoke holes. To flatten the spokes _and_ still be able to fit through a hole not much bigger than the round section of the spoke virtually requires that the ovalized section have a smaller overall cross-sectional area. Such is the case with WS AE15 and XE14 spokes, as well as Sapim CX-Ray spokes, and DT Aerolite and New Aero spokes.

Taking a look at the weights of Wheelsmith AE15, they are basically the same as for their DB15 (1.8/1.55/1.8) round butted spokes (Wheelsmith spoke data), which pretty much guarantees that they have about the same cross-sectional area - in other words, the 2.3mmx1.2mm oval section has about the same cross-sectional area as the 1.55mm center of the butted spokes.


----------

