Maximizing Speed on the Bike: Aerodynamics 101 for Triathletes
Aerodynamics is critical to maximizing efficiency and performance for triathletes and cyclists aiming to sustain higher speeds. Recently, I did some outdoor aero testing with Jim Manton from ERO Sports to see if we could improve my position, specifically my reach, to improve my comfort, power, and aerodynamics. Jim used the GiBLI aerodynamic sensor to measure my CdA, which stands for coefficient of aerodynamic drag. This measure measures how aerodynamically efficient someone or something is.
CdA is a number calculated by multiplying an object's frontal area by its drag coefficient. A lower CdA means a person or object is more aerodynamic and can move faster with the same amount of power. CdA is critical for cyclists in determining how much power is needed to ride at a certain speed. A slight reduction in CdA can significantly impact performance, such as shaving 30 seconds off a 25-mile time trial.
Aerodynamics starts to impact a triathlete at speeds around 10-15 mph (16-24 km/h), but the effect becomes notably significant as speeds approach and exceed 20 mph (32 km/h). Rolling resistance from tires, road surfaces, and weight—especially on hills—are the primary resistive forces at slower speeds. However, once you reach that 10-15 mph threshold, air resistance becomes a more considerable factor in the energy you need to maintain speed. At 20 mph, aerodynamic drag dominates, so optimizing your aerodynamic position and equipment, like a streamlined helmet or frame, can substantially reduce energy use and enhance speed.
Understanding Drag and Its Impact on Performance
Jim Manton from ERO Sports
In aerodynamics, "drag" is the resistance encountered by an object moving through air. For athletes, vehicles, and engineers, managing drag is essential for boosting performance and efficiency. Drag is complex, with several types influencing performance based on an object's shape, speed, and environment. Here's a breakdown of five key types of drag and their relevance:
Form Drag: Also known as pressure drag or profile drag, arises due to an object’s shape and size. When an object moves through the air, it is forced to split around it, creating high-pressure air in front and low-pressure behind, creating resistance. Streamlined designs minimize this by allowing air to flow smoothly, which is particularly important for triathletes adopting a more aerodynamic posture.
Surface or Skin Friction Drag: Originating from the friction between the surface and the moving air. Smoother surfaces generate less drag. Hence, polished surfaces on race cars or streamlined clothing for athletes help reduce this type of drag. Unlike form drag, which is due to shape, surface drag depends on an object's texture and surface area.
Induced Drag: Associated with lift (like that in aircraft wings) and is reduced through streamlined designs to prevent airflow disruptions. In the case of triathlon bikes, induced drag is minimal because these bikes are not designed to generate lift like an airplane wing. However, induced drag can still play a minor role when triathletes ride in aero positions. Specifically, some of the aero bars and specific positions triathletes adopt might slightly influence the airflow around the body, causing tiny vortices or disturbances that resemble induced drag effects.
Interference Drag: Occurs when multiple parts of an object meet, such as where a cyclist's helmet meets their shoulders. Smoother connections between parts help minimize this type of drag.
Pressure Drag Due to Separated Flow: This occurs when airflow detaches from the surface, creating low-pressure zones behind the object. Tapered designs on helmets and narrow wheels help prevent separation, allowing air to flow smoothly.
Practical Tips for Triathletes: Improving Aerodynamics on Your Bike
Aerodynamics is crucial in triathlons for conserving energy and enhancing speed, especially on the bike leg. The following are some areas you can focus on to improve your aerodynamics. However, while some of these, such as aero wheels or helmets, are proven to reduce drag, proper testing is the only way to know if these adjustments improve your aerodynamics.
Optimize Your Bike Fit: Lowering your front end reduces frontal area and drag but must be balanced with comfort because if you cannot hold a position for the length of the ride or it affects your ability to run off the bike, then this lower position may be detrimental. Adjusting your saddle forward can also open your hips, helping you maintain an aero position longer.
Use Aero Bars: Aero bars allow a narrower, more aerodynamic arm position, reducing drag. Consider adjusting the angle slightly for comfort and to keep your head low.
Upgrade to Aero Wheels: Deep-section wheels and rear disc wheels create less drag than traditional wheels, helping to maintain speed efficiently.
Wear an Aero Helmet: Aero helmets streamline head and shoulder airflow, reducing drag. Select one that supports your riding position, with ventilation suited to the climate.
Optimize Hydration Setup: Place hydration systems strategically, such as between the arms, to reduce drag. Remove any unnecessary bottle cages or choose an integrated hydration system.
Streamline Cables and Accessories: Minimize accessories and opt for internal cable routing to reduce turbulence from external components.
Wear a Tight-Fitting Kit: Clothing flapping in the wind creates drag. A well-fitted tri suit with minimal seams and smooth textures significantly improves aerodynamics.
Practice and Perfect Your Aero Position: Gradually acclimate to a lower, more aerodynamic position during training, focusing on core stability and relaxed shoulders to sustain the position comfortably.
Summary
In triathlon, aerodynamic adjustments to gear, bike fit, and body positioning can dramatically improve speed and efficiency, reducing energy spent fighting wind resistance. By focusing on these adjustments and training in your aero position, you can reach and maintain higher speeds while saving energy for the remainder of the race.