Interesting. Were the calcs for spokes in clean air or in the wake of the rim, tire, etc.?
FWIW. Bottom of the tire in contact with the road is zero speed, and top of the tire is very close to 2x speed, but the spoke speed at the bottom end of a spoke is slightly more than zero and at the top end of a spoke is somewhat less than 2x road speed.
Was that on a gravel wheel with fat tires?
I completely agree that fat round spokes are a huge aero penalty. It is a matter of bad natural aerodynamics and large comparative diameter. The big buzz wheels of 20 or so years back were the Magic R-Sys with the big diameter carbon spokes. Those never caught on and from those I know who rode them they were bricks aerodynamically. Material in this instance makes no difference it’s all about drag and minimizing it. A good comparison would be between Cc-Ray’s and carbon bladed spokes. Virtually no round spoke will be competitive vs a bladed spoke. As for durability it’s is not fair to compare aluminum to steel. Steel is far superior. From a strength perspective, aluminum spokes are a poor idea. All that being said, unless we are talking about top level racing for sponsored riders making a living at this, aero gravel is a bit of an oxymoron taking into account all the things needed to make a gravel frame and for strong enough for gravel riding comes with big drag inducing compromizes. Assuming riding gravel for enjoyment which I believe is what most all of us do then it really is not critical. When I built my gravel wheels i prioritized weight and wnet against the grain with shallow carbon rims and Cx-Ray spokes for a 1200 gram wheel and i have no concerns vs my buddies who are all on 50mm or deeper wheels.
There was no effect of rim or tire considered. I doubt they would make enough difference to negate the large difference in drag between round (especially the larger PBO or aluminum spokes) and bladed spokes.
While chatting with Copilot about the spokes and it suggesting other things to investigate. It added that the elliptical cross section is better for off angle wind up to about 10-15 degrees. Whereas the flat spokes (like many current carbon spokes that are 4-5mm wide) perform worse at the same yaw angles and can make handling crosswinds noticeably worse because the flat shape stalls earlier with the air separating causing increased drag and buffeting.
@Caveman, yeah, the aluminum spokes always seemed like a bad idea to me too. As you point out Al is weaker so it appears they make up for it with larger cross section. I made a similar choice as you going with the Terra CLX wheels several years ago. But the new generation of ultra wide, 32mm iw, deep rims probably provide more aero benefit.
What’s the source for any of this?
@Twowkg Copilot AI. The entire chat is attached.
Copilot-RoundVsBladed.pdf (530.2 KB)
As you point out Al is weaker so it appears they make up for it with larger cross section.
Yes and besides that aluminum has a lower fatigue life and limit again making the material a very poor choice for a spoke.