Cycling, Gear, Podcast

Aerodynamic testing in the field with Michael Liberzon | EP#294

 July 12, 2021

By  Mikael Eriksson

LISTEN TO THE EPISODE HERE:

Michael Liberzon is a triathlon coach and host of the Endurance Innovation Podcast. With his background in mechanical engineering, Michael has a keen interest and expertise in aerodynamics, and has plenty of hands-on experience of aerodynamic testing as well as expertise gained from talking to some of the smartest people in the industry. Michael joins us today to discuss different methods of aero testing in the field and the new product category of on-the-bike aero sensors that are starting to proliferate in the triathlon and cycling marketplace.

In this Episode you'll learn about:

  • Aerodynamic field testing methods: pros and cons of different methods, recommendations, and practical considerations
  • On-the-bike aero sensors: use cases, maturity level of this product category, recommendations, and practical considerations
  • Different brands and products of aero sensors
  • How does field testing stack up to traditional aero testing methods (like wind tunnel testing)?

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Shownotes

What is yaw angle?

03:45 -

  • The yaw angle is the perceived angle of the wind towards the rider, if you face a straight head wind, then the yaw angle is zero percent.

    Basically, it’s the combined direction and magnitude of the wind and the rider.

Background

07:30 -

  • My name is Michael Liberzon and my background is as a mechanical engineering, but I rather soon switched to coaching (mainly coaching triathletes).

    In recent years I have been involved as a founder of Stac as well as worked at 4iii.
  • I also host the podcast ”The endurance innovation”, which is similar to that triathlon show, but has a slightly different bend.

Aerodynamic testing

09:40 -

  • When riding a bike, there are five different factors that affect the mechanical energy putting down into the pedals to speed along the road, these are:

    1. Aerodynamic drag

    2. Gravity

    3. Acceleration

    4. Drive train losses

    5. Rolling resistance
  • In order to be able to do accurate aero tests, then these other factors other than aerodynamic drag need to be factored out very precisely (these ”noise” in the calculation must be eliminated in an as exact way as possible).

    Elevation is a huge influent on the speed and hence this one is extremely important to get right.

    This can, however, be achieved by using an out and back loop so that the net elevation is zero.

    Rolling resistance is another very interesting factor, which is important to get right.

    There are several ways to estimate rolling resistance, some of the advanced aero softwares can do it a rather accurate way.

    Drive train losses are small and easy to estimate.

Aerotune system (sensor less)

19:40 -

  • When doing tests with the aerotune, it is very important to understand that you need a very good test stretch in order to get reliable data.

    You also need to do at least two test runs.

    It is supposed to be a 1000m without as many influencing factors as possible (traffic light and even traffic itself influence the data in a quite substantial way).
  • Then you ride this stretch of road as you collect power and speed and from this, the software makes the aerodynamic calculations.

    You get the result instantly in your phone after you’re done, which is a main reason why I like it so much.
  • Another thing I would like to say is that one should always perform the aero tests with training wheels as this makes the system more sensitive (you go slower so the differences are greater).

Sensor based testing

31:30 -

  • Sensor based testing has a sensor in front of the bike that measures the speed and the direction of the wind.

    There are plenty of great sensors that provide good measurements, however, it often requires a longer test stretch, which is hard to find and you don’t get the result instantly as the aerotune testing.

    This is why I prefer aerotune testing at the moment.

”Absolute” CDA

41:00 -

  • To start with, there is no such thing as ”absolute” CDA, in the same way as there are no absolute FTP, it varies from day to day.

    However, measuring an exact CDA on the day is on its way, but there are a few things that needs to be solved, such as barometric pressure.

    However, the question I would like to raise in regards to this is, what point does it have to know this?

    It’s for instant not relevant in terms of equipment choices.

Live CDA

47:15 -

  • Many of the sensor based system did have an ambition to be able to display live CDA so that one can make adjustments based on a value displayed on your bike computer.

    However, since there are so many factors that goes into CDA, this is very difficult to achieve, and hence, many manufacturer has abandoned this ambition.

Different equipment and magnitude of differences

50:00 -

  • In my experience, helmet choice plays the largest difference in terms of gains to be made in aerodynamics, differences between aero helmets can make up minutes over an Ironman bike leg.

    A few of the best tested aero helmets are the Giro aero head, the new Rudy Project (the wing) and the Garneu aero helmet (which is also very cheap!).

    - Tri suits are probably the other major equipment choice that can make a really big difference for speed.

    It is also highly individual and the speed at which you are traveling influence the choice of speed suit as well.

Other interesting performance enhancing gears

01:10:10 -

  • Ways of measuring body temperature in order to analyze the heat’s affect on performance is a field that is on the rise at the moment, and that I find very interesting!

LINKS AND RESOURCES:


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal. Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode. If you are a long-time listener and appreciate the value the podcast brings, please consider taking a couple of minutes for leaving a rating and review on iTunes/Apple Podcasts, or wherever else you can think of leaving a rating and review.

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