Frontal area, surface contour, laminar attachment and differential air pressure.
Feed those elements into your frontal lobe and calculate the drag on a cyclist. My head is aching already. Don't forget air density and turbulent flow.
Aerodynamic optimization is personal. One position may be slippery for one athlete and an air-brake for another. Check out the following side profiles from the FASTER wind tunnel in Scottsdale, Arizona.
These are precise and to scale, all shot from our 120-frame-per-second tunnel view camera centered perfectly on the platform. These show, from left to right, drag grams saving of 15, 555 and 204 respectively over the baseline position for each athlete.
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Cheryl, far right, has an open more upright base position. Eric, center image, is muscular and his best position is chest tilted slightly up and arms wider on bars. Glenn, far left image, has a tucked chest with arms close together on his bars.
Each position is entirely unique due to the multi-faceted effect of presented area, surface contour and airflow. Leading edges are critical, but so are edges on trailing elements and surface contours and texture. Sophisticated computer flow analysis would take many hours to analyze each position.
Here are a few things to keep in mind:
- Each position was the best aero position from a multiple shred session. So that position was in fact most aero. (A shred is an aero session with equipment or athlete. A FASTER shred will typically go from zero to 30 degrees of wind angle positions by 5- or 10-degree increments. Each SHRED returns to starting position and configuration to assure that instruments are recording the entire session with fidelity.)
- Each rider went through full biomechanical FIT optimization and was aero optimized from that most powerful, comfortable, and sustainable position. Zephyr strap and Computrainer was used in the wind tunnel to monitor biometrics and assure the aero position did not reduce pedal power. (Zephyr strap is a super sophisticated chest strap that monitors heart rate, skin conductivity and temperature, breathing rate and torso angle with multi axis accelerometer. Data is passed 50 times per second [50 Hz] by Bluetooth wireless connectivity and self-data stores for several hours of activity.)
- THIS was their faster aero position because of their physiques. One cannot compromise physiques. It is what it is.