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Aero Sensor Companies Start Own Common Aero Device Profile: Got Tired of Waiting for Standard

Cycling aerodynamic sensor companies Notio & Velocomp have decided they were tired of waiting for the long-discussed ANT+ Aero Sensor device profile, and have simply released their own instead. As a bit of a background refresher here, both Notio & Velocomp are the two main players in the aero sensor space, at least in terms of actually shipping units. There’s a long list of companies in the arena, though you’ve likely never heard of most of them. The on-bike cycling aero field is still on the cutting edge of what’s possible, and probably more meaningfully – what consumers are willing to put up with.

Still, I’ve poked at it from time to time over the last…umm…half decade I think? A long time. Almost as long as companies have been trying to formalize an aero-related device profile within ANT+.  Since then, aero sensor companies have come and gone, including one bought by Garmin – Alphamantis, way back nearly four years ago. To date, Garmin hasn’t released a consumer product based on the prototypes that Alphamantis showed off at previous ANT+ Symposiums. Likely for reasons I’ll explain later.

In any event, last week’s announcement from Notio & Velocomp is more interesting than people probably realize. So, I’m gonna try and peel back that onion a bit. Because…why not.

The Aero Profile:

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About two weeks ago, Velocomp and Notio announced the creation and distribution of the “Common Aero Profile”, which basically aims to standardize how devices talk about aerodynamic details in the cycling world. These two companies basically account for all the currently in-production and shipping aero sensors. Velocomp makes the AeroPod, while Notio makes the Notio Aerometer.

To begin, here’s their official press release on the announcement:

“Cyclists expect bike sensors and bike computers to “just work”. Unfortunately, seamless operation between aero sensors and bike computers isn’t possible today because the aero profile—an industry-standard digital “language” used by aero sensors and bike computers to talk to each other—does not exist. Without an aero profile, cyclists might not benefit from CdA and related measurements, because their aero sensor and bike computer can’t understand each other.

 

In order to rectify this problem, two industry leaders in aero sensors, Notio Technologies and Velocomp LLC, today announced a Common Aero Profile. Bike computer and aero sensor manufacturers implementing the Common Aero Profile will provide their customers with a simplified ANT+ setup experience, bike computer display of aero and related data, and device interoperability.

 

“The Common Aero Profile opens up aero-related measurements to over 10,000 Notio and Velocomp customers already using our sensors”, says John Hamann, CEO of Velocomp. “Cyclists get simplified aero sensor setup, and measurements that are received and displayed on their bike computer in a consistent manner.”

 

“A common aero standard has been an industry goal for several years now,” says Martin Lesauteur, CEO of Notio. “As Notio and Velocomp have captured nearly 100% market share of the aero sensor category, we are collaborating to provide a common standard that’s available now. The Common Aero Profile will stimulate growth opportunities for bike computer and aero sensor manufacturers. For cyclists, seeing aero data on the bike computer of their choice, from the aero sensor of their choice, is another obvious win.”

 

The Common Aero Profile will be available for license, without charge, to any bike computer or sensor manufacturer. Notio and Velocomp will implement the Common Aero Profile in their respective products and apps during the 2021 cycling season.”

So essentially, what they’re saying is that because they’re waiting on Garmin/ANT+, they’ve decided to just build their own for now, to get themselves and others (aka, anyone not named Garmin) working towards an actual profile that can be used today. However, they don’t appear to hold any grudges towards the ANT+ profile. In fact, the CEO of Velocomp, John Hamann, noted in a follow-up message that “if and when it is published, and assuming that bike computer companies choose to adopt it, Velocomp and Notio intend to transition to that profile.”

But that “in the meantime, we think the Common Aero Profile will spur near-term growth of aero testing and measurement.” – which, is probably accurate. At this point, some cooperation between aero companies is better than fantasizing about a spec that’s been unachievable for years.

They’re finalizing the exact details of which fields will be included, but the list currently includes: Live CdA, Lap CdA, Wind Speed, Slope, Time Advantage, Lap Marker, Bike Weight, and Rider Weight.

He noted that “it’s pretty easy to go off into the weeds with all the potentially available metrics, but we are going to try to minimize the complexity of the Common Aero Profile…we want to get it ‘out there’ as soon as possible!”. That’s likely some comments directed at the ANT+ profile, which a few companies have noted to me seems to keep getting bigger and bigger to try and solve every possible scenario – ultimately leading to perfection is the enemy of progress. Inversely, to ANT+’s credit, one of the things that they’ve done exceptionally well over the last decade and more is thinking far ahead in terms of compatibility and potential use cases, which ultimately means the standards tend to stick and be well adopted. But I think most would agree that this one simply has taken far too long.

Here’s a slide deck from the 2018 ANT+ Symposium, showing the basic structure of how the TWG (Technical Working Group) works on a new ANT+ Profile. It’s actually a pretty good overview of how ANT+ profiles are created and devices are certified.

Essentially a TWG is a grouping of different companies. So it’s not just Garmin, but Garmin, Velocomp, Notio, AeroLab, likely SRAM, and a pile of others. It’s basically a SIG by another name. There are TWG’s for power meters, trainers (FTMS), and other things. Lots of them, with lots of companies involved.

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Interestingly, the slide directly before the one above used the Aero TWG as an example of a profile under development.

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In any event, Velocomp and Notio’s hope is that the final Common Aero Profile spec will be nailed down in the next few weeks, in time for their products to start using it for the bulk of this season. If other companies want to join in, they’re welcome to.

Of course, the next steps are formalizing this into products that consumers can use. I’d presume that means we’ll see updated Connect IQ data fields that people can record these data points to, and perhaps we’ll see companies like Hammerhead, Stages, and Wahoo support it too as an interim solution.

It’s notable that another aero company – Velosense, has actually been using Hammerhead Karoo 2 units with some of their pro athletes/organizations, and doing so with a sideloaded Android app to record the data into a .FIT file (just like I sideload apps on my Karoo 2). That sort of scenario seems ripe for Hammerhead to come along and say ‘Sure, let’s get these aero fields from the Common Aero Profile added, and make it easy for Velosense at the same time’.

Somewhat ironically – I’ve actually done aero trials of all three of those companies (Velosense/Notio/VeloComp), with all three travelling at various times over the last couple years to Amsterdam to ride test sections up and down the rowing basin.

I caught up with Velosense today via e-mail, and they said they’re interested, and are “strongly in favour of common standards”, and will see if that profile solves some of the gaps. At present, the company is using basically a take on where the ANT+ profile was as of 2020, as a stop-gap measure, with Connect IQ apps for Garmin units, and sideloading on the Karoo 2.

Now finally, one last tidbit that pulls everything full circle is that Notio has long since licensed some of their patents from Velocomp, who has been around in the aero-measuring industry long before it became cool. That’s a piece that may be impacting some of their competitors in various ways, though, from talking to a number of players in the industry, it’s not generally considered a major sticking point.

Aero Product Testing Challenges:

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Some people have asked, rightfully so, why I haven’t released an in-depth review of an aero sensor to date. And the single-sentence reason is relatively simple: I have very low confidence in the ability to do any meaningful data-backed review of such a device at this time.

The more complex answer: It’s really hard. Incredibly hard, to get consistent enough data on these devices that most consumers can use day-to-day. And, for about half of these companies – the goal is indeed day-to-day testing/monitoring of your aero properties. The other half of the companies are geared more towards coaching and analysis services, where an ‘aero professional’ will walk you through the test procedure in person and help you with fit or equipment-related changes.

This second category I have a relatively high level of confidence in. I’ve gone through some of these services in testing over the years, in both beta and production scenarios, and been relatively confident in the data concepts, and data backing. In fact, I’d argue that I was more confident in having the highly trained staff than the technology itself, because frankly the insight of the staff from various companies having done hundreds of tests is more valuable than one specific sensor reading. But doing it on my own out in the wild on real roads with real changes? That’s much messier.

And then taking that a step forward: Actually creating a review protocol that’s objective and data-backed to be able to decide whether or not a product is meaningful? That’s super tricky.

About at this point someone will shout out: Use Virtual Elevation by Robert Chung!

To which I’ll happily respond: I see your reference and raise you the real thing – I spent a day with Robert Chung and Tom Anhalt at an aero facility trying to figure out how to test these repeatedly, reliably, and consistently. And I think we all came away with the same rough thought: Holy @#$#@ this is hard.

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More specifically, it’s hard to have a way to scale this sort of testing outside of side-by-side type scenarios that are heavily dependent on knowing the exact rolling resistance of the road and tires, the exact weights of everything on that day, and the exact wind conditions. And far more importantly than that: The rider’s ability to precisely repeat exact finger and body positions within a millimeter or two. To be clear, it’s not impossible, it’s just tough.

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(Above: Testing AeroLab’s sensors out on the road a few years ago.)

Some of these tests included foam balls hanging off a wooden stick attached to the handlebars, doing ever-so-precise loops around an industrial parking lot. Others involved varying speed tests on an out-and-back stretch. And some even involved wind tunnel time:

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Many questions arose including:

A) First, validating the exact wind-speed of the sensor in question
B) How much is the wind-speed impacted by the riders themselves? (Spoiler: A lot)
C) How does mounting position impact the wind-speed? (Another spoiler: More than it should)
D) Are cross-winds accounted for (yaw angle)?
E) Was there any braking (if so, likely discard entire test)
F) How much distance is needed for each test to stabilize (probably 3-5KM)
G) Did we remember this time to write down every split, and every test variation?
H) Which recording source are we using? The CIQ-data field, or the synced data backend source?
I) How are we analyzing the data to ensure the app itself isn’t tweaking our results?

And that’s just the beginning of the challenges. Which, is ultimately where I’ve paused for now. As Tom, Robert, myself, and others in the industry have poked at – figuring out a repeatable process for testing aero sensors is tricky. Impossible? No, definitely not. But challenging.

(To be clear, this is very different than testing riders using aero sensors – because in that case one is starting with the assumption that the sensor is accurate or sensitive enough, regardless of whether or not it actually is).

I think one is probably looking at having a group of people 3-5 days in a single location together hammering through it all with a bunch of products to see where the testing protocol falls apart during the day, iterating on the analysis at night, and rinse repeating. Just a guess. Maybe twice that. Hard to say.

Wrap-Up:

Now, this isn’t to say these products don’t provide value. I think they can in the right hands. For example, when Notio first started shipping their products, they required all people go to a multi-hour class on how to use it. They literally did a giant global roadshow where people could only buy their products at that class/event. The goal with that at the time was partially to get real-time feedback from early adopters, but it was also to try and minimize people screwing up their products and them getting a bad rap.

I think there’s a fuzzy line between the exact accuracy level these products can achieve their positioning and sensors today, versus what people think they can achieve. In that sense I’m reasonably confident that some of these products can help people, over time, figure out the most aero position for themselves on the bike. For example – someone out there doing their 4-6hr Ironman training long-ride each week in aero position, to sit there and tick off 15-30 minute chunks of different positional tweaks and record the findings, iterating week after week. I think that’s largely viable with some of the products there. I’m less confident in one being able to use this tech for the minutia of gear testing, without substantial time spent on the road with each gear combination.

All of which has nothing, directly, to do with the standard. Except, it probably does.

One has to remember back to Garmin buying Alphamantis, and ANT+ being effectively led by Garmin, there’s a bit of tie-in there to them also driving much of the aero profile Technical Working Group. I’m sure if I asked ANT+ (officially, Garmin Canada), they’d likely just say things were still being worked out by the technical working group. But other members of that TWG have long felt that Garmin’s cycling product group was stalling on their movement forward of this standard. Remember, in this case ANT+ technically doesn’t represent Garmin’s cycling division. That’d be done by people still in Canada, but not part of ANT+ per se. It’s confusing.

What’s not confusing though is that Garmin bought an aero company 4 years ago, started working on an aero profile 3 years ago, and hasn’t released a product based on that. This coming from a company that is actually notoriously expeditious about releasing products based on acquired technology/companies. Which is likely an indicator that they’re trying to figure out a saleable consumer product that doesn’t end up becoming a PR disaster, effectively analogous to what I’m trying to figure out from an aero product review standpoint.

The good news here, if any, is that both Notio and Velocomp have confirmed that if or when ANT+ publishes a standard, then they’ll happily switch over to it. But until then, they’re going to move on.

With that – thanks for reading!

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46 Comments

  1. Rui Pereira

    Just gonna say that this wasn’t what I wanted as a 10m post lunch break before going back to work. Should have drank less wine and more coffee maybe. Don’t know. Anyway, still interesting. Let’s work!!

  2. okrunner

    Garmin won’t make a product or issue a protocol. Ray won’t test it. But, hey, if you’re a 20 something pro athlete with no family, no mortgage, and loads and loads of extra time after your daily workout to sift through near meaningless data, (a/k/a you have no real life) we have a product for you!

    • okrunner

      Oh, and we’ve standardized the protocol for meaningless! I think I’ll stick with the beer widget. Much more useful.

    • It’s tough, really tough.

      I think there’s definitely value in it at some level but I question how many normal users could suss out the nuances when the gains get more and more slim.

      Ironicaly, I think the main benefit at this point is almost as a reminder for when people sit-up or such in an Iron-distance event, as an aero-alert pops-up being like “Here, let me show you how many seconds you’re losing right now…”.

    • usr

      Some interesting “soft metrics” could be teased out long before determining Cda to the third digit, once you bring it all together (odometer, static barometry, GPS, power and pitot). Things like general wind direction over time for solos (did the wind *really* turn against me for the way back home, again, or did I just imagine, like almost every time?), percentage in the lead for groups (with an expected accuracy on the same questionable level as we are used to from “time standing” in cycling dynamics) or a unitless “aero score” that would really just be watts as predicted by powerpod-like-formula vs powermeter watts, with a very generous box filter applied (I’m thinking minutes not seconds).

      All that stuff wouldn’t really be actionable information, but it could be well within the range of curiosity satisfaction as casual power meter use is (and by now the majority of that market is in the casual range I think, yes I’m projecting from myself).

      But: not only wouldn’t you be able to sell a device with that kind of output for hundreds of dollars (for casual power meter use the theoretical possibility that you might also use it thoroughly is an important part of the appeal, even for buyers fully aware of their casual nature), people wouldn’t even bother attaching it to their bike if they got it for free, because extra grams and extra “not aero”.

      So the sweet spot would be integrating a rudimentary pitot directly into the head unit, even if it tripled inaccuracy compared to a would-be scientific sensor. I didn’t think of this when I started typing, but Garmin hasn’t acquired a company in *months*, right?

      Data presentation would be a challenge of course given the casual nature, opening a special pitot app after the ride would quickly get old for low-value data. Perhaps some piggyback options like how wandrer annotates Strava activities?

  3. Alex A.

    I’m an aerospace engineer. I currently work for NASA and used to do wind tunnel testing at sub-sonic and super-sonic speeds. I understand the frustrations of aero sensor calibration and testing with pito-static tubes. In this case, it really is rocket science.

    • okrunner

      Alex,
      Your thoughts are well taken, rocket science is rocket science. This is trying to get consistent aerodynamics of throwing a very soft moving turd through the wind not a streamlined rocket ship. As my uncle who grew up on a farm in Western Oklahoma who worked for NASA for 40+ years would say, “if it smells like bull****, it’s probably bull****.”

  4. Robert Chung

    What a day that was: fun, and frustrating; head-scratching, and eye-opening; refractory, and revelatory.

    • A fun day indeed – even if mentally trying. Also trying…I was trying to find my folder of all the pictures I have of Tom doing loops outside too, but I need to spend some time re-organzing it seems. Only could find my handful of cell-phone pics…

      Eventually I’ll find them.

    • Tom Anhalt

      …loops on an industrial park road, near “quitting time” 😉

    • …all the while his stick and ball were hanging off the side of the bike for all to see.

  5. Paul S.

    I backed the PowerPod on Kickstarter, and acquired an AeroPod afterwards, which I’ve been using for years. I use my AeroPod regularly. It won’t really fit on the mountain bike that I’ve had for over a year now (the cables/hydraulics out front get in the way and the AeroPod won’t really fit; it’s 1x but it came with a dropper post, so still 4 cables), but I still use it on my gravel and road bikes. What I’ve always primarily been interested in is the wind speed (how bad was that head wind?). The power meter is nice, but not my primary interest.

    But I think the market of people that want to improve aerodynamics in a UCI approved way (tuck in the pinky rather than just put a fairing on the bike, which would be much more effective) is pretty small. I’m not sure the AeroPod or any other of these devices have the precision (wind speed always seems to be noisy at about the +/- 2 mph level) to actually do the job effectively. Sure, the number of people that can afford to test in a wind tunnel is even smaller, but at least there you can actually measure the forces.

    • R. Chung

      We can actually measure the forces to a reasonable degree. That’s not the hard part. What’s hard is knowing the separate components of those forces, especially in real-time. After the ride is a much simpler problem. A lot of the training that the real-time sensor manufacturers give is to impose restrictions or regularities on the data collection to help separate the components of drag force to make the real-time problem closer to the after-the-ride problem.

  6. Joe

    I bought a Powerpod about 6 months ago because I thought it would be a good idea for power data in a city (where I didn’t think I wanted to deal with clipping in and out of pedals all the time – and the spider and crank type ones weren’t a good option for my bike). 3 months later I had upgraded to a ‘real’ power meter, because I wasn’t able to get consistent numbers out of the thing. (Also, the calibration process and all of the settings are ridiculously opaque – they need to get a simplified way to set this up in the smartphone app).

    So it doesn’t surprise me that aero data would be even harder. I’d be curious to see some of that data, but as a one time thing and it’s not something I’d care about constantly. But then again, I also don’t do races.

  7. I had the original Powerpod and I was never able to get it set up on both of my bikes so eventually I stopped using it. I decided to try the V3 last year and after what felt like an initial success getting it set up on one bike, doing another bike felt like an exercise in futility. Every time I would set up one bike it seemed like it stopped working for the other bike and I rarely trusted the readings. I’ve since switched to Assioma pedals and couldn’t be happier.

    I feel like there’s a product there that works but the software behind it is atrocious. And if that’s how the Powerpod works, I can’t imagine trying to set up an infinitely more complex aero device.

    • Jim Peyton

      @David T that was my experience as well. I really, REALLY tried to like the Power Pod, but I spent more time getting it set up for every ride than the resultant data was worth. Profiles for different bikes never loaded correctly, meaning the whole calibration process needed to be run each time I went out for a ride. I will cop to some pilot error on my part, but after the Power Pod was bricked during a firmware update, I gave up. To be fair Velocomp offered me a discount on the latest PowerPod, but I decided to go another direction. Obviously this has nothing to do with aero measurements, but given my round profile I doubt it would help 🤣. Hats off to both companies for producing and offering a usable standard — best of luck to them.

    • Joe

      Now that they have Bluetooth, for the last few revisions, they really need to pay some app developer to create an iOS/Android app that you use to set it up. Like – a button on the phone to pair the Powerpod to your speed/cadence sensor (with detailed status other than a LED that flashes a sequence of colors), and then a button on the phone to start your calibration ride (with detailed status of what’s happening rather than a fake power number increasing from 0-50 on your bike computer), then a button on the phone for the return calibration ride, and then a button on the phone to trigger the Powerpod to pair to your bike computer. Just again, something that is more meaningful than a single LED flashing red, yellow, and green.

      And I get how the Newton software could be useful to some pros, but it’s inscrutable to most people, even those of us who are very technical. They need a simplified app that covers the basics.

    • David Hilton

      The problem with the aeropod/powerpod is that it’s marketed as an inexpensive power meter, which it’s absolutely not.

      It can only function as a live power meter for a rider that always rides in the same position with identical riding clothes, or if you’re riding up a hill steep enough that weight is the only consideration.

      Once the rider starts changing their position on the bike, it becomes impossible to produce accurate power data.

      It’s useful as a wind speed sensor or slope sensor.

      If you have a separate power meter suddenly you can calculate CdA or weight.

    • Paul S.

      Define “accurate”. The third party tests I’ve seen over the years, Ray’s included, have all shown the PowerPod to be a pretty good power meter. Yes, you have to realize that your position on the bike affects the accuracy, but the range of motion on a typical bike is fairly limited. Few of us go into the super tuck when a headwind comes up. Calibrate in the position you’re most likely to be riding in (for me, hands on the tops of the brake levers), and you should get decent results.

      With those limitations, you get a power meter that costs about 1/4 of a Garmin Rally and can easily be moved between bikes.

    • Jim

      My V3 bricked just last week doing an update that was called for.
      I did NOTHING wrong and yet I am out one device.
      Not happy.

  8. Andrew M

    I’ve been wondering about where aero sensors were going.

    Thanks for posting an update on the state of the industry, Ray.

  9. Joey

    Boy, that video ad popupsure is obnoxious.

    • You could become a DCR Supporter, and not get ads. But based on your comment history, you seem to prefer just posting comments like this.

      I test various ad types from type to time, this one has been in place a few months now. There’s certainly elements I don’t like about it, and am deciding if it’s worth it or not.

  10. Nooge

    Interesting that all this testing was done with Tom and Robert and it seems even the basic questions weren’t able to be answered. Meanwhile, IIRC both have claimed in various places that they are able to determine aero or rolling resistance benefits of different setups using only typical bike sensors, power and virtual elevation method. That seems contradictory.

    • The key difference is real-time versus post-processing. Robert himself explained this up a bit higher in the comments section: link to dcrainmaker.com

      “What’s hard is knowing the separate components of those forces, especially in real-time. After the ride is a much simpler problem.”

  11. The Aero Truth is Out There

    Seems like these guys are unnecessarily burning cash for such a small market, haven’t reconciled the fundamental complexities of making it easy to inform the user on how to interpret the information and what to fundamentally do to go faster. Post ride analysis for hours is not the answer. Garmin realized this which is why they haven’t launched their product. As well Ant+ is too slow to provide fast response data vs BLE for example. At this point all aero sensors brands are R&D cash burners with no clear value proposition to the consumer market. One could also argue that relative accuracy from an individual baseline is more important than absolute accuracy as you have no way to test the latter.

  12. okrunner

    Ray,
    I’ll likely show my ignorance here, but here goes. Clearly wind is one of the two major forces against a rider, the other being elevation or incline. It’s huge. Riders have been looking at this forever with areodynamics. Sheldon Brown has calculations on it.link to sheldonbrown.com. I’m sure others, like myself, check wind direction in deciding some of their rides. – against the wind going out and with a tailwind coming home. Without using an aero product, could a Garmin or other computer, that is already capable of showing weather, not bring in the wind data and direction during the ride (from your phone of course) and use some algorithm to give you the overall effect on your ride that’s quantifiable and usable. Your gps and compass direction could calculate cross-winds (yaw), for instance. In the list of questions you posed above, couldn’t many of those be answered with this method. I know it would not be the exact condition of the ride, but likely close. An app that would allow you to pick the weather station, so you could bring in the wind information from the nearest, would be ideal instead of just generally in the County, etc. where you live. Here in Oklahoma, there are weather stations at least every 10 to 20 miles, so you could get close to your ride. From there, a rider could begin experimenting like having a daily wind-tunnel data set. Is this half-cocked or has it been tried?

    • Paul S.

      You’re forgetting two huge influences (which you may not have in your part of Oklahoma), terrain and vegetation. Whenever it’s windy here, I head for the mountains of central Pennsylvania (which I can see out my window right now) and the enormous state forest on those mountains. The leaves are just peeking out now, but in a week or two they’ll be fully out and then I won’t feel the wind at all in the mountains, no matter how strong it is in the valleys. The mountains themselves change the direction of the wind even in winter. And of course there are wind gusts, which you do have in Oklahoma. So you really need real time measurement of air speed to do the computation they’re attempting to do. Even in the valley, I’d much rather ride into a head wind on a tree and/or building lined road than a treeless road in farmland.

    • okrunner

      Paul,
      You’re exactly right. I ride through a state park many times on very windy days as it drops into a valley with large cottonwoods on either side and, at least for awhile, you escape the winds. Winds which, in this part of Oklahoma, can gust to 30 mph or more on a regular day. We have alot of wind turbines in the area as this part of Oklahoma has average sustained winds of over 15 mph all year long. Today is “just 16 mph”, without gusts, which is pretty mild. Nobody out here is keen on deep aero wheels for training for obvious reasons. But, pick your poison, I have virtually no elevation to ride. On a short 21 mile route I ride regularly, I have approx. 400 feet of elevation gain.

      I suppose though, if a person were to ride the same route for comparison, the date still might be useful, might?

    • Paul S.

      The 20 mile road rides I do in the valleys gain 1000 ft, while in the mountains 20 miles is typically a gain of 2000 ft. Winds are rarely as high as 15 mph, though, so there is that. (But I grew up in southwestern Ohio, so I know the “oh, sh*t” feeling when you turn into a 20 mph headwind in treeless farmland and start grinding away.) The mountains are nearly 500 megayears old, though, worn down and tree covered, so the relief isn’t that great (the biggest single climb I typically do in a year is about 1400 ft, the local high point is at 2400 and I live at 1200).

    • R. Chung

      So, this isn’t a crazy idea. I think there are a couple of apps that try this, including Best Bike Split, and I think their results are okay. Not great, for exactly the reasons Paul S. has cited, but not complete garbage.

      When I first worked up Virtual Elevation years ago, I called it a way to turn an expensive power meter into a cheap altimeter. At the same time, I worked out how to turn an expensive power meter into a cheap anemometer. So the reason I went with Virtual Elevation and not Virtual Wind is because the road profile is always the same while the wind profile isn’t, so VE was more robust. But, yes, absolutely, if you had external information about wind speed (and direction) at the level of the bike, you can do this (btw, official weather services report wind speed at a height of 10 m, and ground effects typically mean that the wind speed at about 1 m is quite a bit lower).

    • B Osler

      I saw a paper a while back that used an even cruder approach – they used information about prevailing wind for the ride location – and used that as an input to an analysis similar to “virtual elevation”. The authors reported that they were able to obtain meaningful results with the approach which means they were doing far better than I was ever able to do with my Aeropod.
      Part of the problem with the Aeropod’s results is the fact that the wind data are heavily smoothed.
      I’ve also always been a little concerned about the fact that there is no way to verify the calibration of the wind speed measurement.
      Then when you consider the fact that drag is related to the wind speed vector (not just the directly opposing wind speed) and that CdA varies with wind direction it is not surprising that getting accurate estimates is hard.

    • Paul S.

      Way back in Ray’s “First look” post for the Kickstarter PowerPod, a commenter named Osman Isvan posted a link to a paper he’d written about this very thing, how the Newton (the predecessor to the PowerPod in a sense) did as the wind vector changed direction compared to a DFPM. The link to his paper seems to no longer work, but one of his plots is still available in the comment section of Ray’s post. Wind direction is indeed important and a PowerPod/AeroPod can’t measure that (instantaneously; maybe you can get a handle on it with successive measurements). CdA is the constant part of an approximation for drag (well, the frontal area A can change by moving around on the bike, but that’s entirely voluntary), so it doesn’t vary with wind direction, but the drag produced by air resistance does.

    • Marc Graveline

      Hey Paul,

      this one ? link to sites.google.com

    • Marc Graveline
    • B Osler

      That’s the paper I was remembering, though I had forgotten that they used a Newton instead of Virtual Elevation.
      I don’t remember if/how the Newton smooths windspeed data. The Aeropod does a fair bit of data smoothing on the Wind data which might limit the effectiveness a bit but Velocomp claims that the Aeropod wind data are better than for the Newton.

    • Paul S.

      It was the journal article that he linked to. Thanks for finding it. The google link looks like much the same, but it’s dated later than the paper so it might have something additional in it.

    • Marc Graveline

      Bottom line is yaw is an extremely useful data point to look at when trying to explain CDA differences/abnormalities.

      Given both parties that put forward the spec don’t currently measure yaw, I wonder if it’s in the spec.

    • B Osler

      I would not expect either Cd OR A to be constant or independent of yaw angle. The “frontal” area and shape of the cyclist would both be rather different at a yaw angle of 45 degrees than at an angle of zero and because of the different shape I would expect that the boundary between laminar and turbulent flow would be different as well.
      That’s just one more thing that makes aerodynamics hard.

    • Osman Isvan

      Thank you for remembering my article. The source of the Google link was moved from a different web site so it appears to be updated more recently, but it is not different than the journal article.

    • Osman Isvan

      Exactly right! Wind yaw should be in the spec. Actually, the measured quantity is not even wind speed, it is air drag. If the spec must record only one quantity, it should be air drag, not wind speed. In both of these devices, wind speed is calculated from the measured air drag, which is unnecessary but fine, but because the wind yaw is unknown, the measured air drag is not the force acting on the rider; it is the force that would be acting on a life-size cardboard cutout of the rider. These devices sometimes generate accurate data only because wind yaw is small.

  13. Didn’t Garmin accidentally publish a web page a while back with their aero sensor specs? It went live, then was pulled down?

    Andy Froncioni is working his ass off. He knows how hard this is. I’m surprised that you didn’t contact him and include him in this conversation. He’s the true ‘Alpha’ in all of this, and was part of that cabal of intelligentsia with Anhalt and the crew at biketechreview.com (which died last month, btw – RIP).

    My anecdote from the field is that prior to the release of the Rally’s, Garmin was (and is still) testing a unit, and had ironed out the accuracy of the device for road, pavement, and concrete, and of course, tracks. It was the GRAVEL side of things that was vexing them. That should tell you something about the robustness of the product.

    Having worked in this field way back in the beginning, however, you’re right – the data from these sensors is neither accurate nor consistent enough with these devices that they’ve ‘mathed’ over headaches and hiccups and it’s not good enough for training most people, due to drift, setup complexities, plugins to NOAA, slope and RRC inaccuracies, and downright false claims and advertising. Defending these claims for 3 years almost cost me my coaching practice and it definitely put strain on my marriage as I answered calls on weekends, evenings, and holidays while ownership literally went fishing.

    Wait for Andy, Alphamantis, and Garmin. They’ll put the “Robust” in “Robust and Seamless”, and y’all can nerdout all you want after that.

  14. Oliver Johr

    Great report – transparently framed a very complex topic.

  15. Osman Isvan

    I subscribed to Mywindsock.com for this very reason. When I use their wind data to calculate my virtual power in post-ride analysis, the total energy of a bike ride that takes several hours correlates well with my power meter data (PowerTap pedals). In fact, I found the correlation to be generally stronger than that between PowerPod and PowerTap, which was a big surprise to me. But on many rides there are certain segments (up to 10-15 mile sections) where Mywindsock gets it so wrong that it becomes useless for the whole ride. For this reason I much prefer the on-board wind sensor approach of my PowerPod. However, people who are working on wind sensors are on the wrong track, in my opinion. Like millions of other cyclists, I am not trying to see how “aero” I am. I am trying to see my head wind, I want to record it, show it on the map and share it with others, just like my elevation data from an altimeter. Wind data has to be more accurate than relying on a nearby weather station, but it doesn’t have to be accurate enough to resolve CdA in real time. Training and racing with real time CdA data would be great, but this is a niche market. Measuring the wind on a bike ride is not a niche market. To measure your CdA you need to measure your hill slope with great accuracy. You need to know your weight, the weight of the water in your bottle, how much you sweated, your tire pressure and rolling resistance, all with extreme accuracy, even on gravel. To measure wind speed “accurate enough” you don’t need any of that. Garmin doesn’t need anything more sophisticated than a microphone in their Edge devices. But they need to measure wind yaw, so they need two microphones (two differential pressure gauges, to be exact). They are making it harder on themselves than it has to be.

    • Paul S.

      Exactly right. That’s exactly why I backed the PowerPod and AeroPod, and it’s why I still use the AeroPod. I want to know how bad that head wind really was. The power is nice, but definitely secondary, and I don’t have a DFPM, so I have no way to measure CdA. It’s why I use the “Rain & Wind” CiQ field, but many have been the times when that field was telling me that I was riding into a nasty head wind when I was actually riding in the mountains and barely feeling any wind. If there was an Edge with a built in anemometer that displayed real time, that would be perfect.

    • Osman Isvan

      Real time display of wind data is indeed a great feature of the AeroPod and a great application of Garmin Connect IQ. What is disappointing is that neither Alphamantis/Garmin (the group driving the aero-related device profile within ANT+), nor Notio/Velocomp (the group driving the newly-announced Common Aero Profile), appear to recognize and prioritize the need for recording wind data and sharing it on common platforms such as Garmin Connect, RideWithGPS and Strava. The Technical Working Groups are unnecessarily and irrationally hampered by the challenges of syncing the measured wind data with other real time data (accurate hill slope, among others), and making all measurements so robust that they can estimate real time CdA. This level of robustness is not a requirement for recording and sharing the wind conditions encountered during a bike ride. Another disappointment is that the two leading bicycle wind sensor companies, Velocomp and Notio, don’t appear to fully recognize the need for measuring wind yaw. Knowing the wind yaw is not only necessary for calculating the air drag accurately, but it is also necessary for showing the wind direction on the map.