The “Aero-Position”: Why Cyclists Study Aerodynamics

The “Aero-Position”: Why Cyclists Study Aerodynamics

Written by: Riley Walch

Riley Walch is a junior studying Mechanical Engineering at the University of Southern California. He has interests in the intersection of the human body and engineering and hopes to turn this curiosity into a career, upon graduation.

Abstract

Greg LeMond’s 1989 Tour de France victory, aided by research-driven cycling advancements, marked the beginning of the open integration of aerodynamics into cycling. Eventually, progress in body positioning techniques, bicycle componentry, safety equipment and apparel led to the development of an optimal aerodynamic cycling stance known as the “Aero-Position.”

The Moment that Started it All

Perhaps the best example of the importance of aerodynamics in cycling occurred in the final stage of the 1989 Tour de France. American cyclist Greg LeMond, outfitted with his newly designed handlebars and streamlined helmet, as seen in Figure 1, overcame a 50-second deficit in the last 25 kilometers of the race to Frenchman Laurent Fignon, who was riding a conventional bicycle and wearing no helmet at all. LeMond went on to win the Tour by eight seconds, making it the closest Tour de France win ever, a record which still stands today. Many attribute this miraculous comeback to the aerodynamic advantages that LeMond’s gear and form afforded him. Although Fignon’s locks blowing in the wind might have looked extremely stylish, it is likely that they cost him a major win. [1] 


Fig. 1:Greg LeMond in the Final Stage of the 1989 Tour de France, equipped with aero-bars and a specially designed helmet [15].

Had Fignon worried more about performance than his image, he might have been attuned to the research in the cycling realm at the time. This research and testing was conducted on all aspects of cycling, from body positioning to frame and wheel shapes. An overwhelming majority of these findings suggested aerodynamics of the body were the most important and easily manipulated characteristic of cycling. The work of early cycling engineers and cyclists forged the basics of an ideal body position for track cycling and time trial events, giving birth to the modern day “Aero-Position,” which has since been widely adopted due to its superb time-saving abilities.

Behind the Wind: A Look at the Engineering Behind Aerodynamics

Aerodynamics is the study of moving air and how it interacts with solid objects, like  cyclists. A cyclist looking to decrease their time must consider two principles of aerodynamics: wind friction and pressure drag [2]. As school teachers often explain friction, when you rub your hands together quickly, the resistive force you feel is friction, and the heat you feel developing on your palms is energy being lost due to friction. This same phenomenon occurs when cyclists cut through the air on their bicycles; it is called wind friction. The other main component that affects cyclists’ ability to cut through the air is pressure drag. This refers to the principle of pressure differentials, meaning an area with differing pressures will always attempt to balance out to an equilibrium pressure. A good way to visualize this in terms of cycling is to imagine throwing a small pebble away from the end of a vacuum cleaner hose. While the pebble may initially travel away from the hose, it will eventually slow down and change directions to be sucked into the vacuum of the hose. This occurs because of a pressure differential that the vacuum creates. The inside of the vacuum is at a lower pressure than the atmosphere surrounding it, causing the air (and particles in the air) to rush into the vacuum in an attempt to equalize the pressure. This phenomenon is a reason why cyclists experience drag. The area behind a cyclist is at a lower pressure than the air in front of them, causing the cyclist to be pulled in the opposite direction from which they are traveling [3, 4].

Combined, these two characteristics of aerodynamics make a cyclist’s worst enemy: drag. Figure 2, below, presents a better visualization of how drag affects solid bodies. The long-curved lines in the bottom of the diagram can be thought of as the path of a single particle of air. The smoother and straighter the line, the more aerodynamic the body is. As seen in the bottom right quadrant, the pressure drag, or form drag, is reduced when the separation between the lines in the wake is minimized. The bottom left portion of the diagram shows how the wind friction can be decreased with a smoother surface.


Fig. 2:The types of drag a cyclist experiences [14].

Overall, aerodynamic drag accounts for 70 to 90 percent of the force felt when pedaling [3]. Small improvements to reduce drag can lead to major gains in overall performance. New bicycle designs, body positioning techniques, and safety equipment are continually being developed and improved with the help of wind tunnels and computational fluid dynamics (simulated wind tunnels) to push the envelope of how fast a cyclist can go [5].

The “Aero-Position”

The poor aerodynamic characteristics of the human body mean small changes in body positioning can lead to large improvements in cycling performance [1]. Fortunately, changes in body positioning are extremely inexpensive, if not free! Based on the principles of fluid dynamics, a reduction in frontal area leads to a reduction in drag. Therefore, the goal of the “aero-position” is to reduce frontal area.

Because every “body” is different, no two cyclists will have identical positions for maximum results, yet the general form of the position should be the same. Researchers have compared numerous body positions on a traditionally outfitted racing bicycle and have come up with the most effective methods to reduce drag. In a study comparing the different positions in Figure 3, the dropped position and the hill descent position had 20% and 28% less drag, respectively, when compared to the traditional position [6]. This points out two major body positioning factors that help decrease drag, the arms and torso, the only body parts that change positions.

In the most aerodynamic fashion, the arms should be in the center of the handlebar with the forearms angled approximately 30 degrees up from parallel [7]. The torso should also be in a parallel position to the ground. This position, referred to as the “aero-position,” is the gold standard for track cyclists and time trial racers.


Fig. 3: The common cycling positions [6].

Because all bodies are unique, the aero-position needs to be fine-tuned for each rider to produce the best results. In a series of case studies conducted in a state-of-the-art wind tunnel, professional cyclists spent anywhere from 1-3 hours making minor adjustments in their positioning, with impressive results. Cyclist Ivan Basso raised his saddle just 1.5 centimeters and angled his arms up 5 degrees to reduce his overall drag by 11%! And this reduction in drag wasn’t only apparent in the lab. Basso improved his individual time trial results from a 22nd place finish to a 6th place finish, missing his estimated time improvement by just 2%. Other cyclists had similar results, reducing their drag by anywhere from 2 to 17%. These results show that small improvements can result in large gains in performance, with minimal time, cost, and effort [2].

Aerobars: The component that started a revolution

With an ideal body position set, cyclists need an efficient and consistent way to get into the “Aero-Position.” Aerobars are an extension of the traditional handlebar that allow cyclists to rest their elbows close together and have their forearms pointing forward, reducing frontal area and thus reducing drag. As seen in Figure 1, the white bar protruding from the handlebars above LeMond’s hands was the first commercially available aerobar. This component is what started the so-called “aerodynamic revolution” in cycling. LeMond’s 1989 Tour de France victory brought the research engineers had completed in prior years and the handlebars he raced with into the spotlight, showing cyclists that the principles of engineering do not lie [8, 9]. The general consensus about the importance of aerodynamics sent cycling into a frenzy to adopt new technologies and techniques to reduce drag, starting with the aerobar.

Aero-Hats and Skin Suits: Improving the Aerodynamic Characteristics of the Body

Going hand in hand with body positioning and equipment like aero-bars are protective equipment and apparel. One of the biggest wardrobe improvements a cyclist can make is wearing a full body skinsuit. While changing clothing may seem trivial, choosing to wear tight fitting clothing over normal pants and a jacket results in a 30% reduction in drag [10]. Currently, Lycra is one material of choice for cycling because of its low drag coefficient and elastic properties [6].

However, not everything about aerodynamics is logical. Oftentimes, rougher surfaces can actually be more aerodynamic. For example, a smooth golf ball only travels about half the distance of a dimpled golf ball due to the formation of a turbulent boundary layer. A turbulent boundary layer is a region of air that hugs the contour of the ball, and while this turbulent layer increases the frictional drag, it allows smooth flowing air to wrap around the ball more and reduce the wake separation, thus reducing the overall pressure drag to a far greater degree than the increase in surface friction [11]. This aerodynamic principle is being used on cycling clothing by choosing certain areas of the body to have a rougher material than the others and carefully placing seams to reduce the overall drag compared to that of a traditional Lycra skinsuit [12, 13].

The second biggest peripheral advancement is the use of a streamlined helmet. The goal of wearing aerodynamic helmets is to inhibit attached flow between the head and the back. This means tricking the air into thinking that the head and the back are all one surface, eliminating the potential of a lower pressure zone forming behind the head. Helmets with these streamlined characteristics are often teardrop shaped and smooth out the transition from the head to the back, as seen in Figure 1.

Until 2002, the governing body of cycling, Union Cycliste Internationale, did not require helmets to be safe, and it wasn’t until 2003 that helmets were required. This 2003 mandate may have been a blessing in disguise for riders trying to improve their times. Researchers had shown that wearing an “aero-hat,” an unsafe helmet, was far more favorable than riding without a helmet in 1989, years before helmets were required. As the “aero-hat” transitioned into the “aero-helmet” with the 2002 ruling, sizing characteristics did increase but the aerodynamic advantages remained [7]. These rule changes led to an overall positive impact on cycling, improving both safety and speed.

Conclusion

The aero-position is possibly the greatest advancement in cycling over the past 30 years. No other changes have produced the polarizing results that the aero-position brought about.  It significantly increased speeds of cyclists and showed non-technical people that engineering has a place in sport.

References

[1] R. A. Lukes, S. B. Chin, and S. J. Haake, “The understanding and development of cycling aerodynamics,” Sports Engineering, vol. 8, no. 2, pp. 59–74, Dec. 2005. 

[2] K. B. Blair, “Cycling Aerodynamics: Clearing the air,” MIT Open Course Ware, 2013. [Online]. Available: https://ocw.mit.edu/courses/experimental-study-group/es-010-chemistry-of-sports-spring-2013/lecture-notes/MITES_010S13_lec10.pdf. [Accessed: 05-Sep-2018]. 

[3] “Science of Cycling: Aerodynamics & Wind Resistance,” exploratorium. [Online]. Available: https://www.exploratorium.edu/cycling/aerodynamics1.html. [Accessed: 05-Sep-2018]. 

[4] A. Smits and B. S. H. Royce, “Aerodynamics of Bicycles,” Princeton University. [Online]. Available: http://www.princeton.edu/~asmits/Bicycle_web/bicycle_aero_old.html. [Accessed: 05-Sep-2018]. 

[5] A. Mouffouk, “Bike Aerodynamics Simulation – Reducing Cyclist Drag by 30%,” What is FEA | Finite Element Analysis? – SimScale Documentation, 22-Mar-2018. [Online]. Available: https://www.simscale.com/blog/2017/07/bike-aerodynamics/. [Accessed: 05-Sep-2018]. 

[6] C.R. Kyle and E.R. Burke, “Improving the racing bicycle,” Mechanical Engineering, vol. 106 no. 9, pp. 34–35, 1984.

[7] C.R. Kyle, “The aerodynamics of helmets and handlebars,” Cycling Science, vol. 1, pp. 122–25, 1989.

[8] J. Prasuhn, “Was The First Aerobar Really Not The First?,” Triathlete, 19-Jun-2012. [Online]. Available: https://www.triathlete.com/2010/07/insidetri/was-the-first-aerobar-really-not-the-first_11039. [Accessed: 14-Sep-2018].

[9] S. Smythe, “How Greg LeMond’s aero bars revolutionised time trialling,” Cycling Weekly, 09-Jul-2015. [Online]. Available: https://www.cyclingweekly.com/news/latest-news/icons-of-cycling-how-greg-lemonds-aero-bars-revolutionised-time-trialling-181429. [Accessed: 14-Sep-2018].

[10] D.J. Pons and C.L. Vaughan, “Mechanics of cycling,” Biomechanics of Sport, pp. 289–31.

[11] T. Veilleux, “How do dimples in golf balls affect their flight?,” Scientific American, 05-Jan-2004. [Online]. Available: https://www.scientificamerican.com/article/how-do-dimples-in-golf-ba/. [Accessed: 14-Sep-2018].

[12] L.W. Brownlie et. al., “Reducing the aerodynamic drag of sports apparel: Development of the Nike Swift sprint running and SwiftSkin speed skating suits,” 5th International Conference on the Engineering of Sport, Vol. 1, pp. 91–96, 2004

[13] C.R. Kyle et. al., “The Nike Swift Spin cycling project: Reducing the aerodynamic drag of bicycle racing clothing by using zoned fabric,” 5th International Conference on the Engineering of Sport, Vol. 1, pp. 118–124, 2004

[14] “Form drag and tidal flow over topography,” Sally J. Warner. [Online]. Available: http://people.oregonstate.edu/~warnersa/research_phd.html. [Accessed: 14-Sep-2018].

[15] “The Torqued Wrench: A tale of helmet tails,” VeloNews.com, 19-Jul-2013. [Online]. Available: https://www.velonews.com/2013/07/tour-de-france/the-torqued-wrench-a-tale-of-helmet-tails_295882. [Accessed: 14-Sep-2018].

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