Aerodynamic drag is the single biggest force acting against cyclists, as the rider experiences 75% of the drag while the bike accounts for 25%.
The aero drag of a cyclist originates from frictional drag, which is caused by skin friction.
This can be reduced by lowing the roughness of your skin, which is how wearing one of those fancy cycling skinsuit works and can be more easily and cheaply duplicated by shaving the hairs off your body, like your arms and legs.
Specialized & The "Win" Tunnel
Specialized, the bicycle manufacturing company, which also designs components and apparel, has its own wind tunnel, which they dubbed the “Win Tunnel.” In July of 2014, the “Win Tunnel” research team tested the difference between shaved and hairy legs and found that shaved legs was 50 to 82 seconds faster over 25 miles (40km).
Shaved legs = 70 seconds faster on average
So, does shaving arms affect speed and getting “aero” just like the shaved legs?
Cycling: a hairless arm makes you faster
Using the same wind tunnel and research team, 6 months after the shaved leg trial, Specialized assessed the difference between shaved VS hairy arms. Chris Yu and Camron Piper (Specialized researchers) found that shaved arms were 19 seconds faster over 25 miles (40km).
This trial only had one test-cyclist. However, it should be mentioned that he had below-average arm hair. Riders that have a resemblance to Chewbacca will get even more time savings, approaching 22 seconds over the same distance.
On average, shaving your arms saves you an additional 25% of whatever savings you get from shaved legs. Say, for example, if you save 80 seconds with shaved legs, you will save 20 more seconds with shaved arms, totaling 100 seconds over 25 miles (40km).
Shave Pattern & Speed
There is evidence that shaving strategic lines down both your arms and/or legs will lead to even further improvements in aerodynamics. However, unless you have your own wind tunnel or understand Computational Fluid Dynamics, It’s probably best not to worry too much about it.
(Image Source: Godo, Corson, & Legensky 2009)
a hairless arm is a cool arm
“Our cooling system is so superior that in a marathon on a hot day, a human could outcompete a horse.”
A hairless arm is a cool arm, just like a shaved leg is a cool leg. Shaving body hair makes your body more efficient at cooling. Hair holds onto water and sweat, by shaving your arms, legs, or both, sweat evaporates directly off your skin, which helps in lowering your core temperature on those hot days of cycling.
For humans, the primary way we rid the body of excess heat is through sweating. Sweating cools the body through the production of liquid on the skin’s surface that then evaporates, which draws heat energy away from you.
Vigorous cycling generates huge amounts of body heat and in hot and humid climates, it becomes a limiting factor. Mouth breathing is also effective at reducing body heat, as it allows for higher airflow in and out of your mouth.
Sweating & Speed
The faster you go, the faster the air is moving around, which causes you to sweat less, due to quicker evaporation. Just going from .5 mph to 7 mph will double your rate of evaporation and subsequent body cooling at 95°F (35°C). While going faster actually requires more work, simply shaving your arms and legs will lower your body temp.
shaving & style
Some cyclist shaves their legs since it’s part of the “look” of cycling. Shaving arms isn’t as popular among roadies as shaved legs, but it does offer the same benefits…….or a quarter of the same benefits to be more precise.
Final thought
Just shaving your legs and arms, depending on your level of hairiness, can save you about 63 to 102 seconds over 25 miles (40km). To put this in perspective, a few dollars spent on a razor and some cream will make you just as fast as spending $15k on a new high-performance bike.
However, shaving or wearing a skinsuit only reduces one type of aero drag. Form drag or pressure drag, which is mostly related to your position or posture while riding, has an even larger effect on your speed than frictional drag. Even very minor changes in your riding posture have huge impacts on how fast, or how slow you go.
Many recreational cyclists don’t think about how their cycle clothing fits, helmet design, how unzipped their jacket is, or what their arm hair is doing to their time. But just keep in mind that at 9mph (14kph), air resistance becomes your number one obstacle, and every little thing compounds……resulting in 5+ minutes in less than 25 miles.
Jesse is Director of Pedal Chile and lives in Valdivia, Chile. Jesse has a Master of Science in Health & Human Performance and a Bachelor of Science in Kinesiology. Hobbies: MTBing, snowboarding, reading, taster of craft beers, researcher, & compression sock wearer.
Sources:
Adams, W.C., Mack, G.W., Langhans, G.W. and Nadel, E.R. (1992). Effects of varied air velocity on sweating and evaporative rates during exercise. Journal of Applied Physiology, 73(6), pp.2668–2674.
Defraeye, T., Blocken, B., Koninckx, E., Hespel, P. and Carmeliet, J. (2010). Aerodynamic study of different cyclist positions: CFD analysis and full-scale wind-tunnel tests. Journal of Biomechanics, [online] 43(7), pp.1262–1268.
Godo, Matthew & Corson, David & Legensky, Steve. (2009). An Aerodynamic Study of Bicycle Wheel Performance Using CFD. 47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. 10.2514/6.2009-322.
Jablonski, N.G. (2010). The Naked Truth. Scientific American, 302(2), pp.42–49.
Specialized Bicycles (2014). The Win Tunnel: Shaved and Dangerous? YouTube. Available at: https://www.youtube.com/watch?v=DZnrE17Jg3
Specialized Bicycles (2015). The Win Tunnel: Are Shaved Arms Faster? YouTube. Available at: https://www.youtube.com/watch?v=h_C8K9x47q0