You might read this.

Wow!! What a flashback, that was almost 10 years ago!

Short answer is 'no', the wheels are reducing your CdA by some amount that that will hold at all speeds. The whole idea that you had to go a certain speed to benefit from aero is an old wives tale spread by people who didn't understand aero..though sadly, it has hung on for a long time and I still hear it at bike shops around the world!

The article shared was a test we did where we ran at 20 and ran at 30 and then mathematically scaled the data..it was more to show people that the math works. In modern terms we would likely redo that using CdA, but in 2007, the explanation of CdA alone would have required it's own article! What an awesomely long way we've come since then.

The only speed related effect here will be yaw, going faster will reduce your average yaw, being slower will increase it. Most of the modern wheel designs have been heavily optimized for higher yaw, and have done it with little to no effect at lower yaw, so 'modern' wide bulbous rim shapes will generally sit on the efficient frontier of aero between 0 and maybe 12 or even 15 degrees which is going to be about 75% of your real world yaw at 20+ mph.

Best
Josh

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

One of the wild quotes in that article is "For an average age grouper, 15 degrees is going to be about the most statistically common wind angle, but for pros, it is more like 10 degrees as they are averaging higher speeds, which reduces the apparent wind angle." Recent studies by two or three aero players have since refuted this. There was another post in a recent ST thread wondering where this misconception came from, but it is at least 10 years old.

Yeah, we've learned a lot in 10 years.

This raises the question, if you can ride at 23 mph, why are you riding at 21 mph? I am going to suggest you ride at 23mph if possible instead of 21 mph, no matter what wheels you are on.

Thanks for the Friday morning laugh.

I suppose if there was any condition where an 808 would be most beneficial, it would be in strong crosswinds (which is usually when people avoid using these wheels because they push you around).

So the original method for coming up yaw angle came about with the democratization of GPS. We could take wind speed and direction from weather data and overlay it into GPS vector data for real events and get theoretical yaw distributions. We later started using handheld Kestrel anemometers out on course at events like Kona and the TdF and then using that to be an almost live prediction of the distribution..

I think that what is being discovered now is that the actual windspeed near the ground is reduced even moreso than we thought, we used to take Kestrel measurements at 1m for consistency, seems that was maybe too high..we also used to reduce weather data velocity by 50% as it was typically taken on a 3m pole, but maybe that should have been more. I think too that most of the real world data we were taking was at pro events where you are way more likely to have point-point type racing rather than a loop. We even had a lot of data from Kona, but I was there and those were windy years! I remember recording steady 20mph crosswind out on course in kona in '04, somewhat similar to when Triathlete used the Mavic whirligig device and found large swaths of Kona to have probable yaws in the 10-20degree range over much of the course despite using a strong athlete with ~24mph average pace.

More importantly though, I'm not so certain it matters all that much as the focus on higher yaw designed us into rim shapes that more or less live on the efficient frontier of disc wheel performance. Most of the modern rims that are awesome at 12 or 15 degrees are no worse off at 0-5 unless you are on skinny tires.

So an old 404 was similar to a disc from 0-7 degrees, then the original 808 was equal to a disc up to 12.5 then the Firecrest got us to 15+ and all while tires were getting wider..and it's the wider tires and not the wheel that are dominating at the low yaw angles. Ultimately I think that most aero wheels are going to be within a few % of each other below 7 degrees and it's what they do after that which separates them from each other..

This was largely what began to drive us to stop looking at speed and start focusing on handling in the 2008-2010 timeframe. The wheels had gotten to be extremely fast, even with the tires people were actually using, but I would go to events and people would be riding a front training wheel because they were scared to ride their deep or 3 spoke wheel and that really became the new opportunity, aero wheels that you could and would ride all the time.

Funny to note how this article focuses on the wheels working with the 'wide' 21 and 22mm tires of the day! As trail said, a lot has changed!

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Great follow-up, and the comment about actual wind speed near the ground totally makes sense. I think I have seen similar statements on several other bicycle aerodynamic web sites or studies.

And, it does appear that wheels are getting very similar performance across the board. It seems like everyone's wind tunnel marketing reports show that their wheels are better than everyone else's. This only works if everyone is lying, or the differences are so small that it is marketing interpretation that is defining the differences. And, I am glad that I will benefit from better handling when I eventually buy my first set of wheels.

I saw that too, and I laughed a little. I used to road race back in the late 80s and early 90s, and back then, the skinniest, highest-pressure tire was the unicorn. I raced on 19mm tires when I did not use my tubulars. They were harsh. I still have a set of 80s era 1" tires on my Schwinn Le Tour that I converted to my first triathlon bike. Who knew those tires were so fast? Now, I have 25mm tires, and it would not surprise me much if everyone started to race on 29mm tires.

I think all of us have had that thought.

The optimal speed is the fastest speed you can average without blowing your run. But what's that? (Besides it isn't speed, but power. Speed is a poor choice for primary performance data, because it depends on factors you can't control like wind, elevation, and road surface.)

Very well at stating what would seem the obvious the average person - but I'm looking at WATTS. I needed a laugh also - thanks.

Great article - thanks for the reply. I believe I have my answer.