Cycling faster without extra wattage? Sounds too good to be true, but it's possible. In Airo 101, we delve into the world of air resistance, speed gains, and smart cycling choices. Because if you understand how aerodynamics works, you'll cycle faster without necessarily having to pedal harder. In this series, we'll discuss all the relevant factors, from materials and position to clothing and wheels. In this first part, we'll lay the foundation: what is CdA and why is it so important?
CdA explained: Coefficient of Aerodynamic Drag
In the cycling world, CdA is a well-known term, as it's the key to faster cycling. The abbreviation CdA stands for coefficient of aerodynamic drag , or the resistance you experience as a cyclist as you move through the air. The term consists of two components: Cd (the drag coefficient) and A (the frontal area of you and your bike). Cd indicates how streamlined you are in terms of shape, position, and material, while A represents the frontal area of your body and bike.
The Cd and A values together determine the amount of air resistance you have to overcome as a cyclist. A low CdA value means less air resistance. And less resistance means you ride faster at the same power. Or, in other words, at a constant speed, you don't have to pedal as hard. Above 30 km/h, air resistance accounts for over 90% of the total resistance you have to overcome (Kyle & Burke, 1984), so the lower the CdA value, the better.
However, while CdA plays a significant role in how fast you ride, it's not the only factor affecting your speed. Rolling resistance , climbing resistance , and gravity also play a role. Some aerodynamic choices may lower CdA but add weight or force you into a less effective position, preventing you from gaining speed. In short, the overall picture has to be right.
The shape matters
While many people automatically think of "less drag" as "being smaller," the story is much more nuanced: CdA isn't just about compactness, but even more about shape . How the air flows around you, your bike, and your clothing determines how much energy you lose to drag. Take, for example, round brake cables that run externally: they may seem small and insignificant, but their shape creates a lot of turbulence. Wind tunnel tests show that a simple 5 mm round shift cable can have as much drag as a 5 cm wide, aerodynamically shaped head tube, simply due to the difference in shape (Lukes et al., 2004).
This difference is partly due to pressure drag : the air resistance created at the front of an object when it disrupts the airflow. But just as important is friction drag : the resistance caused by the friction of air particles moving along the surface. For objects with an unfavorable shape or surface, airflows diverge at the rear, creating a zone of low pressure. This zone essentially "sucks" on your bike, slowing it down. Therefore, it's worthwhile to consider not only the size of components, but also their shape and how the air around them behaves.
These insights also explain why modern bicycles and accessories look very different from ten years ago. At first glance, an aerodynamic helmet appears to be primarily a large surface area, but the "tail" at the back, which fills the air gap between the head and back, prevents the airflow from prematurely escaping. The result: up to 7% less drag compared to no helmet or a standard model (Kyle & Burke, 1984).
Why material and surface make the difference
It's not just the shape that matters; the material and surface texture also play a major role. Smooth isn't necessarily better. Sometimes, a textured surface actually helps control airflow, creating fewer turbulences. This is where clothing, accessories, and components come into play. Think of aero socks, specific sleeve fabrics, or base layers that channel air instead of blocking it, for example, through strategically placed seams. In wind tunnel tests, a well-designed aerosuit reduced drag by up to 6% compared to a standard suit (Kyle et al., 2004 & AeroPro, 2021).
Airoman.cc also develops its products based on this kind of knowledge. How exactly does this work and what factors do we consider? We'll cover that in detail in part II of this series. We'll then explore how clothing design, fabrics, and fit can benefit your CdA value.
What can you do as a rider now?
You don't have to be a pro with access to a wind tunnel or a custom aero suit to gain an aerodynamic advantage. Even with a standard road bike and your current equipment, you can significantly reduce drag and thus cycle faster without expending extra power.
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Posture on the bicycle. A low, compact posture—think bent arms, elbows close together, and a still head—reduces air resistance by up to 28% compared to an upright sitting position (Grappe et al., 1997 & Olds, Norton & Lowe, 2020). Even without wind tunnel testing, you can make an immediate difference with this.
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Tight clothing. Loose-fitting shirts or flapping sleeves increase your frontal area (A) and cause unnecessary turbulence. Well-fitting outfits are therefore essential. Airoman.cc clothing cleverly addresses this: with close-fitting cuts, air-flowing material, and strategically placed seams, every detail is designed to reduce CdA (Kyle et al., 2004).
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Clean cockpit. Protruding cables, loose handlebar bags, or other accessories create additional drag. If cables aren't neatly concealed, they can contribute up to 10% of a frame's total drag (Zdravkovich et al., 1996). A tidy handlebar is more than just aesthetics; it's free speed.
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Riding in a group. The simplest aero hack? Drafting. In the lee of a group, air resistance decreases significantly, by up to 50% with ideal positioning (Blocken et al., 2018).
In short…
What all this demonstrates is that aerodynamics isn't an abstract technical matter for pros and gear enthusiasts. It's something every cyclist, at any level, can make a direct difference with. By being aware of how air moves around you and your bike, you can make smart choices to get more speed from the same power. CdA isn't a number for wind tunnel reports: it's a shortcut to better performance. And the better you understand that number, the faster you can go with the same wattage.
In the next installment of Airo 101, we'll delve deeper into aerodynamic clothing and the difference that the right fabric, fit, and seam placement can make. This will be followed by sections on posture, material selection, and other factors that influence CdA.
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Sources:
- AeroPro. (2021). Wind tunnel testing or AeroPro race suits .
https://aeropro.uk/pages/wind-tunnel-testing - Blocken, B., Toparlar, Y., Andrianne, T., & van Druenen, T. (2018). Aerodynamic drag in cycling platoons: New insights using CFD and wind tunnel validation . Journal of Wind Engineering and Industrial Aerodynamics, 181, 262–279.
- Grappe, F., Candau, R., Belli, A. & Rouillon, J. D. (1997). Aerodynamic drag in field cycling with special reference to the Obree's position. Ergonomics, 40(12), 1299–1311.
- Kyle, CR, Brownlie, LW, Harber, E., MacDonald, R. & Nordstrom, M. (2004) The Nike Swift Spin cycling project: Reducing the aerodynamic drag of bicycle racing clothing by using zoned fabric. In: 5th International Conference on the Engineering of Sport, Vol. 1 (Eds, Hubbard, M., Mehta, RD & Pallis, JM) UC Davis, USA, pp. 118–124.
- Kyle, CR & Burke, ER (1984) Improving the racing bicycle. Mechanical Engineering, 106(9), 34–35.
- Lukes, RA, Hart, JH, Chin, SB & Haake, SJ (2004) The aerodynamics of mountain bicycles: The role of computational fluid dynamics. In: 5th International Conference on the Engineering of Sport, Vol. 1 (Eds, Hubbard, M., Mehta, RD & Pallis, JM) UC Davis, USA, pp. 104–110.
- Olds, T., Norton, K., & Lowe, E. (2020). Reducing aerodynamic drag by adopting a novel road-cycling sprint position . Journal of Science and Cycling, 9(1), 22–29.
- Zdravkovich, MM, Ashcroft, MW, Chisholm, SJ & Hicks, N. (1996) Effect of cyclist's posture and vacinity of another cyclist on aerodynamic drag. In: 1st International Conference on the Engineering of Sport (ed. Haake, SJ) AA Balkema, Sheffield, UK, pp. 21–28.