The club ride guide to…aerodynamics
Aerodynamics is one of the most talked about topics in cycling. Everyone looks for ways to get that little bit faster for the same power output. The effects of aerodynamics can vary from saving a few watts here and there, to beating your friends to town sign sprints or even winning world championships. This article breaks down the basics of aerodynamics and the science behind the funny looking kit cyclists roam around in.
Aerodynamics concerns how fluids (in this case air) interact with moving objects. When you ride a bike, you’re pushing against air molecules, and they push back; this is called drag. The faster you go, the more noticeable drag becomes. More specifically, drag is directly proportion to the square of the objects speed (Drag α speed2), in other words, if you double your speed, the drag force acting on you increases by a factor of 4 (quadruples). This is why increasing your speed from 20 to 40kmph is much harder than going from 10 to 20kmph.
The drag acting on a cyclist is made up of two components: form drag, and skin friction drag.
Form drag is caused by the shape of the cyclist and bike. The larger the frontal surface area of the moving object, the larger the form drag. Cyclists will try and get their head and torso as low as they can on the bike (ie. “getting aero”) to reduce their frontal surface area and therefore reduce drag. Narrow and slammed bars are a common sight amongst cyclists, helping them get as streamlined as possible, along with a great deal of stretching to inevitably still end up looking like a shrimp on the bike.
Skin friction drag is caused by caused by the air rubbing against the surface of the cyclist’s clothing and bike. It’s smaller than form drag but still matters, especially at high speeds. Smooth, tight-fitting clothes help reduce skin friction drag as it gives the air a cleaner path to flow along - this is where skinsuits and lycra come into play. Rough or loose-fitting clothes disturb the air flow making it turbulent. In simple terms, turbulent air flow is “messy” air flow that increases skin friction drag.
To avoid this, cyclists use kit that help the air flow past them in smooth parallel layers. An example of this is the ribs seen on the shoulders and arms of skin suits and base layers; the ribs force the air to flow past the cyclist’s body in straight lines, minimising turbulent flow. Rubber overshoes are another piece of kit that make a significant difference in reducing skin friction drag as shoes are cutting through the wind with each pedal stroke. If the surface of the shoe is irregular, it disturbs airflow, making it more turbulent. Overshoes streamline the shape of the shoe by holding down any flapping or protruding parts and create a smooth surface for the air to flow past.
Straight, parallel air flow around a smooth object (top) vs turbulent air flow around an irregular object (bottom)
Wind tunnel testing is a method that is used to study how air flows around an object. A wind tunnel is basically a big tube with powerful fans that blow air through it. The cyclist is placed on a static bike in the wind tunnel and instruments are used to analyse airflow patterns around them. Often wind tunnel testing involves calculating the cyclists CdA. The CdA of a cyclist is their drag coefficient (Cd) multiplied by their frontal area (A). The drag coefficient is a measure of how efficiently an object's shape reduces drag. It captures the complexities of an object's design, such as its streamlining or if it creates a lot of turbulent air flow. The frontal area is the cross-section of the object that faces the wind, which is calculating using front facing images of the cyclist in the wind tunnel. A lower CdA means less drag. Engineers can adjust the shape, position, or equipment and immediately see how it affects the CdA of the cyclist and therefore what changes will result in less drag.
Aerodynamics is a complex branch of engineering that is constantly evolving and driving innovations in sports to improve efficiency, speed, and performance. The level of effort you dedicate to aerodynamics should reflect a balance between cost, practicality, and the improvements you expect to achieve. Of course, if you don’t want to be spending all your savings buying the latest aero kit, you can always just sit in for the whole group ride and come around everyone for the sprint back into town.
The CJ OSHEA Bioracer kit provides outstanding aerodynamic performance
