That's pretty interesting.


I've done some virtual wind modeling. At the time when I was doing that was before I had a gps so I didn't know which direction the bike was traveling but when I did laps I could definitely see characteristic "virtual wind" patterns within laps. Since I didn't have gps, I found that virtual elevation was more robust, so I went with that. But if I did have gps, I could see it being nice as an additional check. Very clever.

I saw this tweet of Roglic in the wind tunnel and it looks like an aero sensor on the front above the front tire - https://twitter.com/.../1382658115070476288

Wonder why they'd do that.

what also appears to be a clever use of the data is their use of regression to tease out CRR. They assume that the CDA is constant at varying speeds and therefore the difference is CRR...so in their system if you do multiple runs at different speeds (as I understood from the podcast) then the software will work out the CRR. Their software solution sounds interesting. The person they were interviewing mentioned Chris Morton as well, which might be where the two came to the similar approach to being able to get at CRR? Chris discussed this on one media that they simplified the solution and found that if things were constant then they could calculate the CRR from a similar type approach as I recall. This is all just math (says the guy who is no mathematician) so hopefully the smart people who set up the Chung method in Golden Cheetah could add this sort of thing in the platform.

Golden Cheetah actually has a Estimate Cda/Crr function.
Getting the data formatted to run it isn't that straightforward but the math is there.
It requires data points at a known altitude or laps. It requires setting all altitude points not at the known altitude or lap start/end to 0. It builds up a set of matrices and solve's via Cramer's rule.
I don't know if Robert used it or not or if he has better magical math.

Wow marcag, you guys are smart... I did not know that had been implemented. I seem to recall that in a new update to Golden Cheetah there was a plan to update the Chung method functions to make them more user friendly. I have not looked at it recently because we are just now starting to get out side to ride after the winter in my part of the world and well it still is too cold to do aero testing out doors. Robert has all sorts of math magic in his tool box it seems! one can only hope! but the news that this is implemented is very cool.

According to the source code It was done by a guy named Ale Martinez who I believe is a STer.

Yes I have seen Ale pop up here and I should acknowledge his mathematical wizardry, well done Ale!

Quite a bit more reach and stack, too:

Probably calibrating the aero sensor so they can relate outdoor and tunnel data.

Interesting that it does not appear to be a pitot style. Wonder if it's similar to the anemometer bugno/Pierre utilized. IME the data seems as good as other sensors.

I am sure the data is as good. I bought one, but haven't yet used it. I believe the only app that reads it is Pierre's which isn't available anymore.

Down side of this sensor is it doesn't do yaw. It's pretty easy to do on a pitot these days.

My guess is that isn't an anemometer destined for outside use. The mount doesn't look like something you'd ride with, but we're speculating.

Well a meaningful amount of that seems like how he's on the saddle. One, rivet. Other, back.

It's VeloSense. The giveaway is the stem sensor that gives data on chest height AFAIK.

This is just a guess, but I'm guessing that's not the way it works. We've long known how to solve for both simultaneously (Galton figured that out in the 19th C.). The issue is that if you don't get a wide enough range in speed and power, and if there are things that interfere with the test run (like, a passing car or a momentary use of the brakes because a dog ran out in front of you or an unusual gust of wind), regression isn't very robust. So I do use a regression approach to get "starting" values for Crr and CdA but then I check a bit more and tune a bit if needed. Tuning requires a way to assess the fit or lack of fit. That's what VE is. That's why I say VE is a diagnostic.

thank you Robert it is very possible I did not understand the implications of what I thought I heard. It is so cool though that the method you have developed with VE is such an elegant method.

Today I was playing with a power calculator otherwise known as on line bike calculator and though I intuitively knew temperature had an effect all else held constant I was surprised how much of a difference it was between 5 and 25 deg C. for a simple calculation the difference to go the same 30 kph speed at 5 deg vs 25 was 10 watts more at 5 deg C that blew my mind and at the same time gave me hope since my last couple of rides have been at 5 deg C so if I was riding somewhere warmer (and wearing less clothing which probably further influences that number I would be going faster for the same power...this topic is always so interesting.

Don't forget another 25% of watts for rolling resistance

yeah to make myself feel even better I explained to myself the reason I was so slow was, 1- my gravel bike, 2- it is steel and well not the lightest, 3 riding through sand and mud / clay roads 4- riding Gravel king SK tire which I have to say made my bike feel like a new beast but the aero thing still gets me when I think of the temperatures, air density, extra layers of clothing, etc all adding to more drag and therefore more power to go forward. CdA is such a drag!

It's the effects of humidity that always blows my (and others) mind...it's totally counter-intuitive, in that most think of humid air as being "thick" ;-)

---

http://bikeblather.blogspot.com/

I think you are right: https://www.velosense.com/sensors-cycling

They've been around a few years but still no products available for bikes?

Have you written Pierre? The GooglePlay link to the app seems to be broken, but he has posted recently and I doubt he would have killed it: https://cdacrr.blogspot.com/

One thing I like about the anemometer is that when using it, my CdA seems to be impervious to yaw. In other words when I zero the distance averaged headwind and compute CdA I'll get the same value on a calm day vs one with gusting crosswinds. YMMV.

What would you actually do with yaw data, anyway?

yeah it is sort of counter intuitive until you remember that the molecular weight of water is less than both oxygen and nitrogen. Plus cold air is also drier.

Yes, I have written to Pierre. I think he is in a situation where he can't provide the level of support he would like to. VERY understandable, and probably one reason why vendors are hesitant to release product at large. The support load is pretty big.

There are at least two advantages to having yaw. So far, the biggest has been correcting certain signals (at least 3) that do depend on wind direction. I also see that my Cda is NOT impervious to yaw. That being said, 90% of my rides are in wind conditions of > 5km/h, often over 10. I intentionally ride a various yaw angles as I refine this.

I think they are close to release something, but I don't know what their intended market is.

Yup. I've done that. After I'd convinced mysself I could turn an expensive power meter into a cheap altimeter, I wanted to know if I could turn an expensive power meter into a cheap anemometer.