Advanced, Cycling, Podcast, Science, Training

Cycling Science and Myth Busting Part 1 with Stephen Cheung | EP#74

 November 9, 2017

By  Mikael Eriksson

Cycling Science and Myth Busting Part 1 with Stephen Cheung | EP#74

Stephen Cheung, Ph.D., is the co-editor of the newly released book "Cycling Science". He discusses key cycling questions and what we know and don't know about them from an evidence-based standpoint, while still making it understandable and actionable. He might even bust some myths.

In this Episode you'll learn about:

  • (The science of) Cycling body types
  • (The science of) Bike fitting
  • (The science of) Aerodynamics
  • (The science of) Rolling resistance

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About the book Cycling Science

03:47 -

  • It started in 2012 with my first book called Cutting Edge Cycling that I wrote with Hunter Allen, the US-based cycling coach.
  • About a year or two after, the publisher Human Kinetics and I decided to go bigger and better. We developed almost an encyclopedia of cycling science knowledge.
  • It’s really comprehensive. It has 40 chapters on a really wide range of topics.
  • We partnered with my co-editor Dr. Mikel Zabala from the University of Granada in Spain. He’s also the sports scientist for the Movistar Pro Cycling Team.
  • Together, we pooled in through our various contacts as many real experts in the field as we could to contribute to Cycling Science.

Cycling body types

06:07 -

  • In triathlon and in cycling there is something to fit everyone. There is not necessarily one optimal body type.
  • Many triathlons are really based on aerodynamics as a time trial. There may be climbing, but most of the triathlon courses tend to be flatter.
  • It's not necessarily an advantage to be a relatively bigger individual, though, because it’s not necessarily about the power to weight ratio. It’s more about power to frontal surface area.
  • But in a larger individual, their surface area often isn’t proportionally that much bigger than a smaller individual. That really helps explain why a bigger individual can be very strong in a flat time trial where the main priority is absolute power output and minimal surface area.
  • Whereas as a climber, it’s really not about the absolute power but about the power to weight ratio.

Bike fitting

09:37 -

  • There is a melding of both science and art when it comes to bike fitting.
  • One of the challenges in the biomechanics of cycling and the science of bike fitting is the difficulty of teasing individual components, such as crank length, and just studying that in isolation.
  • For example, most of the research that has been done looking at crank length suggest that there’s no real benefit in terms of power output.
  • We usually think of a longer crank being useful for increasing the leverage. Whereas a smaller crank can make you accelerate faster.
  • But in terms of absolute power output, the studies that have been done have shown that there’s really minimal difference in terms of the absolute power that you can generate with either short or long crank.
  • Another difficulty is with the scientific design. For example, let's say I’m used to a 170 mm crank and that’s what I’ve been riding for a long period of time. If I suddenly switch to a 165 mm crank and I only use it for the testing session in the lab, I haven’t really adapted my body to that.
  • Even if there are acute differences that we may see in the lab, the body is really adaptable. After a few weeks on a different crank size, your body is going to compensate for it.
  • To date, the science of bike fitting in a sense really isn’t there. There are a few studies, but no consensus in results. For all we know, as long as you’re in a relatively moderate setup, you’re not at one crazy extreme or the other, tweaks within that is more about fitting you anatomically to the bike rather than maximizing efficiency or power output.
  • There are overall general rules of thumb that are good as starting bases. From there, the focus really should be on accommodating an individual and their optimal fit.

Key takeaway

  • There really isn't much in the way of research-backed bike fitting practices.  

Aerodynamics, rolling resistance, and gravity

13:21 -

Frontal surface area

  • The frontal surface area is really the overall key in terms of how much air you’re pushing. In a sense, it's the Holy Grail to minimize that aerodynamic frontal surface area.
  • This can be done with the bike in terms of its shape or wheels, or it can be done with the clothing. However, 80% or more of the aerodynamic drag comes from the body itself.
  • You want to get the best bike fit that you can. That’s going to minimize your surface area.
  • The trick is that it's a balance between being in a really low drag position yet being able to generate the power. It’s very easy to minimize the surface area but can you still generate power with it?
  • In order to improve the ability to generate power and minimize the stress to the body in an "extreme" position, there has been a trend towards shorter crank lengths so that you can maintain a relatively open hip angle even in a very aerodynamic tuck and also decrease the strain for the running segment afterward.

Rolling resistance

  • The trend is towards wider tires and wider wheels to have more volume and less rolling resistance, which science does seem to support.


  • This is where the trade-off for aerodynamics and weight comes into play.
  • The challenge with a lot of aerodynamics such as really deep disc wheels, besides worrying about crosswinds, is their added weight.
  • At what point does the added weight become more of a penalty than an advantage? The answer to that depends on the speed that you’re going at, and also the grade you're riding up.
  • If you’re really fit and an elite level triathlete who is doing your bike segment at 40 km an hour or faster, then aerodynamics really play a huge role. You can get away with focusing mostly on aerodynamics as opposed to weight on a rolling course with some hills up and down.
  • Whereas if you are an age-group triathlete where you might be averaging 35 km an hour or less for your bike split, then aerodynamics become a little bit less of a factor and weight can become more of a factor.
  • It’s a constant balancing act between the speed that you’re going at and also the elevation profile in your particular course.
  • The third angle is also draft-legal and non-drafting triathlons. If it’s a draft legal triathlon where you can be spending a lot of time sitting behind your competition in a group, then aerodynamics don't play as big of a role.
  • Compare this with if you’re in a non-drafting situation where you are hitting the wind the entire distance. Aerodynamics become critical because there’s no one breaking the wind for you except yourself.
Aerodynamics, gravity and rolling resistance

Republished from "Cycling Science" with permission.

Since the body itself account 80% of the drag, does that mean that the first thing to focus on is getting a bike fit?

21:24 -

  • Yes, the priority is an optimal bike fit for a couple of reasons. One is to maximize that aerodynamic advantage and to minimize that frontal surface area. Second is for your long-term health and prevention of injury.
  • If we arbitrarily try to go for the most extreme aerodynamic position possible and just do it on a random basis, we may be extremely aerodynamic. But we can be setting ourselves up for long-term injury issues.
  • Getting an optimized bike fit will greatly help in the long-term because you can train harder and minimize injury-risk. As a result, you’re going to get faster.
  • Depending on your finances and on the type of racing that you do, the next priority is to invest in an aerodynamic helmet and/or a good set of aerodynamic wheels. These are next two biggest things that will be hitting the wind.

Key takeaway

What is the benefit of sitting with the pack in draft-legal racing? How much less power do you have to produce?

27:01 -

  • You really can’t overemphasize the difference between being able to sit in a group versus having to ride solo in the wind the entire way.
  • Let’s say you are up at the front and you’re riding at 300 watts. You’re the one breaking the wind.
  • The guys who are two or three riders behind you buried in the middle of the pack are probably riding at about 210 watts. They’re saving about 30% of the energy because there’s minimal wind hitting them.
  • So, there’s a minimized aerodynamic drag. Most of the resistance comes from rolling resistance and gravity. There’s a huge slipstream effect.
  • Anyone who has ever tried motor pacing or even when a truck or car pass you as you’re riding along knows that feeling. You’re just able to accelerate so much more and maintain a higher speed.
  • Even if you are in a non-drafting triathlon where you’re about to pass an individual that you have stayed 10-12 meters behind. Depending on the speed, you can still get a bit of a draft even at that distance.
  • You can use that to your advantage if you are passing someone to really accelerate in that slipstream to get that little bit of a slingshot effect.
  • If you’re not comfortable riding behind another person, sitting on a wheel very closely, then you’re going to be losing a little bit of aerodynamic benefit and expending more watts and energy than you need to.
  • They key is to be comfortable in that pack environment to be able to place yourself in a correct spot knowing where the wind is going to be so that you’re maximizing your energy efficiency throughout.

What is ideal tire pressure?

33:10 -

  • Over the last 10-15 years, I’ve gone lower and lower in my own tire pressure. Part of it is because I’ve started racing cyclocross a lot where the whole emphasis is on as low the tire pressure as you can get away with.
  • I remember when I started racing back in the 80s and the tires were 20 mm. I had them up to 120 psi all the time. For the longest time, I thought you just need your tire to be as hard as possible because that’s going to minimize rolling resistance.
  • I’ve learned over the last 15 years that I actually want to be going with lower and lower pressure because most of the roads that we ride on are not necessarily perfect smooth.
  • If you are riding on a velodrome on a track where the surface is really good, then you would want to have high tire pressure to minimize that rolling resistance.
  • As soon as we get on to the normal roads that we ride on where it may be rough, anytime the tire is balancing off the ground, you are not able to maintain forward torque on the tires. You’re really slowing down anytime your tires are bouncing off the ground.
  • Most tires are meant to have that little deformation as you sit on the bike. This deformation is around about a 15 millimeter drop. This is to allow the tire casing to conform to the ground to get a more comfortable ride.
  • You’re also going to have better grip with a little bit extra surface area. The tire casing is able to better conform to the ground. You’re going to get better traction both in a straight line and also in the corners.
  • I now ride 25 mm tires and regularly go 75 psi in the front tire and 80 psi in the back (at 64 kg body weight).

Key takeaway

  • You're probably riding too high tire pressures for the road surfaces that you ride on. 
  • See Stephen's note on riding at 75 and 80 psi to get an idea of how far you can go. 

Links, resources and contact

Links and resources mentioned

Connect with Stephen Cheung

Connect with host Mikael Eriksson


Hi! I'm your host Mikael,

I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.

I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show. 

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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.

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