Cycling, Gear & Technology, Podcast

The latest on aero sensors and aero testing with Michael Liberzon | EP#339

 May 23, 2022

By  Bernardo Gonçalves

LISTEN TO THE EPISODE HERE:

Michael Liberzon - That Triathlon Show

Michael Liberzon is a Toronto-based triathlon coach, bike fitter and aero tester, and host of the Endurance Innovation podcast. In this episode Michael discusses the currently available options on the aero sensor and aero testing market, how they differentiate from each other, and what's to come in the future with new sensors and improvements of the currently available options.

In this Episode you'll learn about:

  • What aero sensors and testing options currently exist on the market, and how do they differentiate from each other?
  • Michael's personal experience in aero testing, including using the Notio sensor and the Aerotune sensorless system
  • What kind of athletes would benefit from doing aero testing, and considerations if you want to get started
  • Michael's current recommendations for potential buyers
  • Expectations and predictions for where the field is going in the next few years

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Shownotes

Aerodynamic sensors

04:43 -

  • Most people understand the importance of reducing aerodynamic drag in cycling and triathlon, where it is only one against the wind. (there is no drafting)
  • In that "battle" against aero drag, we have some tools: the most proven has been the wind tunnel, which is expensive and time-consuming.
  • There have been exciting developments in CFD (computation fluid dynamics): these are computer models that researchers use to obtain the aerodynamic drag of a cyclist and optimise the position.
  • My co-worker Andrew developed one of these models called STAC Virtual Wind Tunnel.
  • There is also a system from the Swiss Side and a couple of others.
  • The final ones are the field aerometers/aero sensors.
  • It is a device you would put on your bicycle to measure airflow. By communicating with the other sensors on your bike or sensor in the unity itself, the aerometer calculates your drag area (CdA). It allows you to decide how to change your position/equipment to become more aerodynamic and ride faster for the same power output.
  • In a recent podcast episode that I did with the founder of Swiss Side, his hot take was that there was no such thing as "live CdA" currently to give your aerodynamic drag.
  • His caveat about this equipment is that you can obtain "live data" from at least the last 20 seconds. Therefore, you cannot get instantaneous values, but you can get a reasonable average number of the last 20-60 seconds.
  • I believe that is possible, but I have not used a device so far that can do that today.
  • The devices that can do this will come up in the next 12-24 months.

Absolute CdA value

09:40 -

  • No one has an absolute CdA value because even if you are an excellent experimental designer, where you can maintain variables constant, your CdA will differ depending on wind conditions.
  • The apparent CdA that the cyclist experiences depends on wind conditions. (wind speed and direction)
  • If the wind changes direction slightly (effective yaw changes from 5º to 15º), it will significantly affect your CdA. If you make a 90º turn, your CdA will be different.
  •  It is the reason why manufacturers present data by doing a swipe from 0º to 15º yaw angles.

Best aerometers to acquire

12:28 -

  • The first one was the Notio. They were an Argon spin-off, and they were the first sensor on the market and the first sensor that I purchased and got experience with over the last months. Moreover, anyone can go on the website and purchase them.
  • Another Canadian company is Aerolab. Their business model is different, and theirs focuses more on teams and coaches. You would get this device with much support from Aerolab and build it into your business model.
  • I have not had much experience with Aerolab's sensors because they are costly. The Notio is around 600 US$. As Aerolab focus more on the professional user, the prices are much higher for the end consumer.
  • Gibli has a ready sensor, but unfortunately, they got caught in the chip shortage, so Gibli will launch their product as soon as they solve this issue.
  • These are the currently available sensor options on the market.
  • Aerotune is a sensorless product which is also available. However, they are developing a sensor, but I am not sure when that sensor will be available for purchase. They have some prototypes that they tested in the field with good results, so it is another sensor I am looking at shortly.
  • Bodyrocket has some interesting sensors located in different places on the bike. (they do not look only to the free air)
  • Nevertheless, you want to place these sensors in the cleanest air possible. By clean air, I mean air that first hits your bicycle. You do not want to put a sensor on your seat tube because other elements affect the airflow at the seat tube.
  • Bodyrocket has a different approach by placing more than one sensor and might develop something in the future.
  • Swiss Side is a well-regarded company in cycling aerodynamics coming from Formula 1. They have been developing a sensor for many years.
  • However, according to them, they will release it only when it is perfect. I suspect the sensor will come out soon.
  • There is another company called Streamlines, which is a spin-off from Velosense. 

How the sensors differ from each other

18:16 -

  • They are all trying to capture the same thing: giving the cyclists a CdA value.
  • With the current technologies, aerodynamic testing is possible to do.
  • For example, I want to determine if helmet A is faster than helmet B in specific conditions.
  • In this scenario, all these sensors try to do the following: give you a CdA value and quantify the differences between the different configurations.
  • What makes aerodynamic testing very challenging is the whole stacking of air. 
  • As a cyclist, you put power in the pedals that transmit to the back wheel. So, some things hold you back when you ride.
  • The first thing is acceleration. When you accelerate, you need to add more power, but if you are riding at a steady speed, it is something we can eliminate.
  • Then, we have elevation changes. Anytime you go up a hill, you increase the system's potential energy ("cyclist + bike"). If you add potential energy, that energy has to come from somewhere. (your metabolic energy)
  • Of course, going uphill is more demanding than going on flat roads.
  • Rolling resistance is the energy required to overcome the resistance of the interaction between your tires and the ground.
  • The magnitude of this resistance is not massive, but it is pretty complex. Before, we thought that higher pressure was always better, but you have two components of rolling resistance that we have to consider when analysing performance.
  • The last is drivetrain drag, the power loss between your foot and the read wheel.
  • An efficient drivetrain is 2 %, but it can be as high as 5-6 %.
  • We need to capture it, but it is repeatable from test to test.
  • The fifth is aerodynamic drag.
  • We know the rider's power output through a power meter to calculate aerodynamic drag. We know how fast we are going, so we need to consider the other four forces to understand what is holding us back.
  • We have to measure specific things to obtain those forces and the sensors that allow us to measure them come with errors.
  • If you claim with an aero sensor that we will give you an accuracy of 2 % (wind tunnel accuracy), you will be able to choose between helmets. Still, you need a reliable and consistent value for your aerodynamic drag.
  • The stacking of the errors when measuring other losses can obfuscate what you are trying to measure.
  • If each of the sensors that are measuring the other losses has a 1 % error, 
  • For example, you need a speed sensor to get instantaneous speed data because GPS lags. GPS is suitable for capturing distance and average speed, but it is not suitable for capturing acceleration and slowing down.
  • The most complex challenge to solve is elevation. Even relatively minor elevation changes can result in significant differences in the results.
  • Nowadays, we use altimetric barometers. These barometers constantly fluctuate, so the values can change over time, even if you are not going up a hill.
  • Even the most accurate GPS monitors barometric altimeter can deliver non-sense altitude data. And to calculate aerodynamic drag, any error in altitude data will affect the results because of the potential energy sink.
  • People developing aerometers are solving this problem with the software.
  • They use some sensors to verify this data (barometric altimeters use IMUs to detect angles and movement in 3D). These devices can help correct the altimetric data.
  • If you can create a program to solve the issue, your data will be more accurate. That is why Swiss Side is taking a long time to release its products.

Sensors that Michael used

28:30 -

  • The only sensor I have been using is the Notio.
  • The Notio in good conditions is a reasonable sensor, providing that you can check the elevation gain is minimal.
  • I have used the Notio for 18 months, and the beginning was complicated. First, we would have to upload the data to Golden Cheetah to perform the elevation correction to obtain a correct CdA.
  • Since then, they have developed an app where you do the test and sync the device with your phone, and it would give you one value. I have good experience from that. Some people say that you still have to be careful with the elevation to see if it will return to zero, which is essential.
  • The Notio is a good product which is straightforward to use.
  • I have much more experience using the Aerotune platform. Aerotune only uses the speed from the speed sensor, power, and elevation data and does not measure wind velocity.
  • They perform repeated passages of the same out and back terrain to reduce the error signal. It works well if you set up the experiment correctly.
  • The trick for using Aerotune is to use a flat smooth stretch of road with minimal traffic. Therefore, its application has limitations.
  • They have guides on how to perform these tests to obtain valuable data.
  • Another advantage of using Aerotune is that it is very affordable.
  • You pay 20 € per month, and you can use the platform as many times as you want.
  • This system is not ideal because weather conditions change, and your data will also change. One thing that Aerotune presents is the error and the calculated wind conditions.
  • There are guides on the weather conditions. For example, if the wind is higher than a specific value, you might not consider those results.
  • You can avoid this issue with aerometers that accurately measure wind speed and direction.
  • However, if you are only changing clothing, helmets or hydration settings where you do not have to take out components of the bike, in a 4-h session, you can get good data on 5-6 different set-up configurations. It will only depend on how much riding you are willing to do as an athlete.

Michael's reasons for using Aerotune

34:27 -

  • I have dug into the Aerotune system and had long conversations with the founder, and I have much more confidence in the values presented than I would with the Notio system.
  • The problem with the Notio is that the elevation correction was not perfect. I did out-and-back tests, and I would find differences in elevation.
  • As the elevation plays a significant factor in the CdA calculation, it erodes my confidence in the device.

Athletes that should do aero testing

35:46 -

  • I think this would be useful for anyone curious. I would advise people to treat it as an experiment, but you need to have a good idea of what we are trying to do as any good experiment.
  • You should have an idea of what you want to achieve with testing and if you want to evaluate.
  • With aero testing, I would advise people to be patient.
  • Aerodynamic testing is not something you might get right at this stage in product development. You have to do many things correctly before things make sense, and you can make decisions from the test results.
  • If you have that, you will find that those small things that you thought would not affect the results significantly impact performance.
  • Head position was something I was surprised about when addressing aerodynamic optimisation.
  • Therefore, I think everyone curious and patient with these protocols should do these tests.

Recommendations for athletes

38:15 -

  • There is a sensor in the market that I would be excited to recommend.
  • There are some that I would like to try when I can get my hands on them, and I am curious to see how that sensor stacks against Aerotune, for example.
  • There are also two engineers working on a GIZMO. (two-men development project)
  • The most exciting products for me are Aerotune. They have a well-built platform. And also, the sensor from Swiss Side because they spent more time developing the sensor than anyone out there.
  • Therefore, for now, there is no sensor that I completely trust.
  • The advantage of Aerotune is that it is inexpensive and easy to use.
  • To perform testing, you want a Dual-sided power meter. I favour single-sided power meters because of the cost reductions, but in this case, you want a Dual-sided power meter to have absolute power instead of "left leg times two power".
  • You need a power meter, a speed sensor and a GPS unit. And then, you only need to find a good road segment.
  • They have road segments of 500 meters and extra segments on each side (800 meters).
  • If you find a good road segment near your neighbourhood, it is perfect for testing.
  • Then, you only need to ride there and see the numbers you obtain. Regularly, people that have never done aero testing have much to improve on, so you can compare it to other athletes and see if you are fast or not.
  • You can choose whether you want to share your data, and there are many users and people interested in the community, and they will share the results with it.
  • You can also take photos that you can attach to testing, and people will give you free advice. And in this platform, most of the advice will be pretty reasonable.
  • While you cannot do a loop circuit with Aerotune, you can do it with aero sensors.

The future of aero testing

42:37 -

  • There is some hardware that I am excited about in the following years with Swiss Side, Aerotune.
  • Many people have been working on this topic for ten years, and we are close to having a good product that you can put on your bike and not worry about the course too much, ride and get valuable data.
  • You will not need to set up a test and use the equipment in regular training. The goal is to build the test into your training, even if you do not have live CdA. Even if you get the head's movement and the CdA drops by 0.02, having this in your training can avoid losing training sessions for testing.

Additional comments on aero testing

44:39 -

  • If you want these services with an expert in the field, you can find many people, especially in Europe.
  • If you want to invest in aero testing and become faster, there are different resources, and for example, it is something that we do on a smaller scale in Canada.
  • We can parallel this to coaching. You can learn all the things a coach knows, and if you have the time and desire to do it, hire a coach.
  • It would be best if you treated it as an experiment.
  • You can evaluate the fastest helmet and skinsuits because it is more straightforward.
  • But if you want to obtain the significant variations, those come from changing your position on the bike.
  • Going for a position that is still biomechanically functional but more aerodynamic takes some experience. The people that went through the process and understood the details will be better than those that will only do this by trial and error.
  • Moreover, there are not many robust generalisations concerning the position. Specific things work often, but very few things always work. However, for equipment, it is not the same.
  • For example, we know that a deep wheel will be faster than a shallow wheel, regardless of your position. A disc wheel will be faster than a regular wheel. However, concerning position, optimisations will depend on the individual.
  • For example, the mantras position for half of the population will be faster. Still, for a non-trivial percentage of the population, it will be slower because of the different shapes of our bodies and the way the flow moves around the body.

LINKS AND RESOURCES:


Bernardo Gonçalves

Bernardo is a Portuguese elite cyclist and PhD student in the field of aerodynamics at the University of Coimbra. He writes the shownotes for That Triathlon Show, and also produces social media content for each new episode.

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