The FASTER wind tunnel in Scottsdale Arizona approached us to contribute content. We requested that it not be an 'advertorial' but informative in its own right. This first installment, by tunnel engineer Jay White, deals with how different physiques demand different approaches to aero positioning.
Aerodynamics for cycling ‘the scientific application of body position to reduce drag forces’
by Jay White © 2012 FASTER
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, AZ.
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. 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 = 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…
The FASTER wind tunnel in Scottsdale, AZ provides a great venue to explore your own, unique, and fastest position. In addition, we can rotate the platform 350 degrees to any wind angle to duplicate a specific range you may expect during your next outing on the road. Analysis is dynamic [presented in graphic format in real time on our Speed Lab control room computers] and results and data are available right after your session is complete.
As you will see in the above images, an athlete’s side profile has a HUGE effect on control forces that need to be generated by the rider. Present more side area, and winds hitting from angles as slight as 15 degrees, can easily mount up 7 to 9 kilograms [16 to 20 pounds] of side force! Translation: side forces have a component of drag that not only pushes you sideways, but also SLOWS you down!!! Calculate 7 Kg of side force at 15 degrees of wind angle and you get 1.81 Kg drag force [15.4 pounds of side force @ 15 degrees = 3.9 pounds of drag force]. That’s a lot of engineer talk to simply say that you need to look at more than your frontal profile to consider all aspects of aerodynamics and how they affect whatever type of events you are participating in.
So keep wheels in mind and side profile of the bike and accessories in mind. Look at Cheryl in the far right image: rim profile = minimal so side profile is minimized. Cheryl was on shallow wheels because they were the wheels she planned on using for next event. She can handle deeper wheels but utilizes wind – course terrain data to optimize wheel selection.
We outfitted Eric [center image] with a rear disc and front tri-spoke, and then outfitted him with a set of 92mm deep rims as shown, and the 92mm wheels reduced his drag by 555 grams! Just because you THINK something is aero fast does not make it so… Deep rim wheels have significant drag from the side area presented at wind angles from 5 degrees and up. That means deep rim wheels can be SLOWER due to increased aero drag depending on the average wind angle the event.
Every athlete is unique in size, build, flexibility and strength. That means predicting your aerodynamic drag is almost like predicting someone’s intelligence by looking at their photo!!! Sometimes accurate, but also very possible to be way off!
Lastly, holding an aerodynamic position and making sure your body is not compromised in its power delivery is critical. If your cardiovascular efficiency is inhibited by a contorted aero position, you may not be able to sustain power to your pedals. At FASTER, we utilize wireless biometrics so that heart rate and breathing rate are monitored while your aerodynamic drag is measured so you finish totally optimized at the intersection of greatest power, lowest drag, and most efficient respiration. This assures (unlike other wind tunnels) that you can go out and have your best performance ever (barring training, nutrition, and personal factors) without having to experiment with what you just learned in a wind tunnel session.
The best and most cost efficient way to get at superior aerodynamics is to make a visit to the FASTER wind tunnel and get blown away!
Jay White is the FASTER wind tunnel engineer, a triathlete and a mountaineer who has climbed Everest. Jay specializes in electronic analysis of complex shapes and rapid movements for tailored product designs. For more information on the FASTER wind tunnel, visit: ride-faster.com.
On cannot ride on water and mightiness alone, and as I age, I find that I have to pay more attention to my nutritional needs, lest I become an empty husk of veiny gristle.
The fall is here and winter will soon be upon us.