I think the answer is that all time "counts" as far as energy expenditure is concerned thus the higher the sampling rate, however "noisy", the better. Given the shape of most yaw distributions we have and the fact that most samples have been taken at ~1hz (iirc) I think we can safely conclude that the resulting yaw distribution skews low. Maybe not much, but at least a bit.

I'll throw this out there: Josh Portner (Silca/Zipp) recently let an interesting tidbit slip. Zipp did some testing where they went from 30 degrees to 0 degrees to see when the flow would reattach and they found that reattachment did not occur at the same angle as detachment for the rims they tested. Instead they found that flow didn't reattach until a lower yaw for most rims. He also hinted that shapes that performed better at higher yaws saw their flow reattach sooner when going from 30 to 0 degrees. For most modern rim/tire combinations we see today flow seems to detach around 12-15 degrees. For all the modeling that's been done (that I'm aware of) it has been assumed that a given wheel's performance from 0-20 degrees is the same as its performance from 20-0 degrees. Separation is admittedly rare for most riders but, again, this is a consideration that might be biasing us toward low yaws in design and equipment selection.

Something that has always bothered me, personally, is that we test in the tunnel with the front wheel perfectly aligned with the frame when, in reality, the wheel is constantly moving a few degrees back and forth from zero. If I had the time, I'd figure out a way to hook up a servo encoder to my headset to gather data.

...rambling here....

If we think about what happens when a side wind hits a rider, the wind tilts the rider/bike away from the direction of the wind which causes the front wheel to turn back into the wind. The rider then counteracts this and resets the system. In this instance, if you had two different yaw sensors attached to the bike at two different places (the handlebars and, say, the top tube) you'd get two different readings for two different parts of the system. If I'm thinking about this correctly the frame would see a higher yaw than the front wheel. The unknown for most of us is how the front wheel down tube system works when the two aren't aligned. It would seem to me the most pragmatic approach would be to include the steering deviation (1, 2, maybe 3 degrees) from center and add that to the yaw distribution that the wheel "sees" as the goal is for the flow to stay attached to the front wheel and then transition smoothly to the down tube.

Wrapping up my ramble here...

In light of the forgoing, perhaps we should be looking more closely at the performance of our equipment at higher yaws.

Edit: this might also make one reconsider tire selection as some fast rolling tires really hinder the performance of a wheel at higher yaws. The Turbo Cotton and GP TT come to mind.

There's a reason you're sampling at 200Hz though, and it's because you are not getting 200 accurate measurements per second out of your ICs!

Ease of use.

As I understand you need for the Velosense, as for the Aeropod, a speed sensor.
And that is a step back for me. After all the hassle with spokemagnets and interference from overland power lines and so I am very glad since a couple of years now to have finally rather a stable speedometer thanks to GPS.

This is what the Aeropod and Velosense should have: internal GPS for speed. (I guess it is not possible to get the speed from another GPS device: which is in fact the reason that use must be made of the archaic speed sensor).

One should also not forget that the Velosense and Aeropod do not show a true CdA: if you go from smooth tarmac to rough tarmac the measured CdA changes (as I understand the devices) although the real CdA stays the same of course.

Can I take advantage of your presence here and derail this thread a tiny bit? What is your preferred turbulence model for external aerodynamics simulations - particularly when there is a significant turbulent wake?

I just looked at this Daimer truck CFD analysis where they conclude the Spallart Allmaras DES model compared very favorably with wind tunnel tests at lower computational cost than an LES model, while RANS was off by 20%. It's 5 years old - would something like the k-omega-SST Improved Delayed Detached Eddy Simulation be better?

Thank you so much!!

I prefer to do field testing with a wheel with a PowerTap hub. That way, driveline loss uncertainty isn't an issue

when you bring up your point about the point of attachment/reattachment above, this is (to me) the lost dynamic in wind tunnel testing. i'm willing to concede to all you guys who are much smarter than me that tunnel testing closely matches road dynamics in the broad sense. what animates me much more today, tho, is the capacity to handle the bike, and the abrupt changes in steering torque when the wheel abruptly stalls just to rediscover laminar flow. or whatever terms i should be using if i knew anything.

but there are 3 "yaws": 1. the apparent wind; 2. the frame; 3. the front wheel. which means when you attach any sort of a gauge to the front wheel, showing its angular variance from the frame, you're not seeing its total angular variance from the apparent wind, because the frame also is at variance from it.

second, when you bring up your point about the point of attachment/reattachment above, this is (to me) the lost dynamic in wind tunnel testing. i'm willing to concede to all you guys who are much smarter than me that tunnel testing closely matches road dynamics in the broad sense. what animates me much more today, tho, is the capacity to handle the bike, and the abrupt changes in steering torque when the wheel abruptly stalls just to rediscover laminar flow. or whatever terms i should be using if i knew anything.

tom is going to find out whether his device's output lops off the high points in the chart and how much is lopped off.

but, i think if you listen to what john buckley says, that's not it. i believe he thinks his device has the capacity to see yaws that other devices don't (and so don't record).

maybe this has big implications for which wheels are truly fast.

but we still are left with whether we can ride these wheels without crapping our pants.

...unless you shift gears (sensitivity of the strain gages varies across the cassette).

I think you misunderstood, and I'm sorry if I was unclear...what I intend to determine is what is the inherent "noise" in the yaw measurement for my Aerostick device. In other words, you're pointing at 2-4 deg "oscillations" as indicative of something that's actually happening at the wheel, and I'm trying to figure out how much of that (0.5 deg? 1 deg? Something else) is just measurement noise. I don't believe it's "lopping off" any high yaws, since as I showed in the plot above, I can easily cause it to record high yaw angles just by performing a 180 turn at low speed.

Well, to be fair, that's not always JUST on the wheel itself...IME, other equipment (and positioning) choices can have a big effect on the "ride-ability" of a given wheel. Things like running a rear disc, the geometry and trail of the front end of the bike, a comfortable bar position, etc...

Slowman wrote:

...the only product that really interests me is the new ceepo bike, because it has the capacity to damp steering torque. but i digress.

As long as we're digressing...on the subject of damping steering, I think I've mentioned this before but I acquired a used version of this Hopey steering damper product (damps excursions away from center, free on return to center) that I've always wanted to try on the front end of a TT bike, with the hope (pun intended) that it would even allow the "comfortable" use of a front disc wheel outside :-)

http://www.hopey.org/tt-triathalon.php

(Oooh...I see they appear to have mounts now for integrated headset cups...I may get my chance to finally test it out on my P3!)

So, I guess there's more than one way to tackle this "issue" ;-)

I just realized...it would be interesting to see the yaw recordings from a ride where that damper was turned on and off. That would be one way to gauge how much steering input has an affect on the yaw measurements, and how much a damper does, or does not change things. Hmmmm....

FWIW, lots of runners also place unjustified faith in GPS...apparently they have never actually looked at their recorded tracks.

but we still are left with whether we can ride these wheels without crapping our pants