Aero is short for aerodynamic and can be defined as “the way air moves around things” (1).  Becoming more aero has been an ongoing quest for athletes, bike manufacturers, clothing companies, bicycle accessory producers, and even water-bottle businesses, but why?  Can becoming more aerodynamic really improve your overall speed and finishing time?  And what is the best bang for your buck when trying to reduce aerodynamic drag?

Aerodynamics is the way air moves around things.

Unbelievably, Brownlie et al. (2) showed that wind resistance accounted for 72%-90% of the force resisting the forward motion of a rider, and the faster the rider goes, the more resistance they have to overcome.  Imagine if you are swimming through water and compare that to swimming through Jell-o.  Swimming through water would be similar to riding a bike at slow speeds when there is not much wind resistance, whereas riding a bike quickly would be like swimming through gelatin with lots of resistance present.  Other factors that have been shown to affect forward motion of a rider are tires 15% (rolling resistance), braking losses 8%, and bearing/chain losses 5% (3).  Wind resistance can also be called aerodynamic drag and can be defined as “the force on an object that resists its motion” (4).

Aerodynamic drag is the force on an object that resists its motion.

Factors that contribute to aerodynamic drag

  1. Body position is the largest contributor to aerodynamic drag and has been shown to be upwards of 75% of the total drag experienced by the rider (4).
  2. The helmet can contribute 2-8% of the overall drag with more vents creating more drag and vice-versa (5).
  3. Wearing clothing that is tighter fitting and utilizes zoned fabrics (smooth in areas and dimpled in others) can reduce drag by 10% (6).
  4. Cycling shoes that have laces versus shoes that utilize straps and shoe covers can, unbelievably, differ by 8% in aerodynamic drag (7).
  5. Jermy et al. (8) states that wheel drag accounts for 10% of the total aerodynamic drag when a cyclist is traveling 30-50kph.  Ideally, the tire width should be equal to the rim width to further minimize drag (9).  When there is no crosswind, disc wheels are best, but 3-4 spoked wheels (HED) are best in crosswinds.
  6. Bike frames, when made as aerodynamic as possible, can reduce drag by as much as 14%, but usually average a 3% reduction compared to a traditional round-tube frame (10).

As you can see, there are some pretty substantial reductions to be had if you have the resources to capitalize upon them.

Time savings when becoming more aero

Okay, let’s get down to brass tacks here; will getting more aero and investing in aero equipment really make a big difference?  The answer to this question is a resounding YES!  Lindsey Underwood (11) wrote an amazing thesis regarding the aerodynamics of track cycling and calculated time savings as well as average reduction in drag for each equipment change:

Capture
Credit: Lindsey Underwood

The above chart describes time savings in seconds over the course of 4000m on a track, but these can be extrapolated to any length.  Imagine the time savings over the course of a 40k TT or even an Ironman!?  The best thing about this is these savings will not cause the rider to use more energy, and will help the rider conserve their energy to be used later during the finishing sprint, or run in a triathlon.  So, you can produce the same amount of wattage, but go a heck of a lot faster!

What is most influential for reducing aerodynamic drag, i.e. where should you spend your money?

The above pictures are an excellent comparison of not only how far the technology of cycling has come, but also the science of aerodynamics and how it relates to cycling.  Granted, the technology did not exist in the old days to create what the cyclist on the right is using, but just look at the two of them; even if you knew nothing about aerodynamics you would probably guess the rider on the right would be going a lot faster.  Although, the old-school rider definitely wins in style points and dapper looks.

So, where should you spend your money?  Refer to the chart below:

Capture 1
Credit: Lindsey Underwood

A bike fit is by far the pinnacle of reducing aerodynamic drag and something I highly recommend to my athletes.  Second is surprising to most, but is actually investing in a skinsuit.  I see many people spend a ton of money on their bike and wheels, but miss the fact that these two make up a small percentage of the wind resistance holding you back (although they make you look so pro).  Remember, to reduce drag most you need to reduce your surface area and frontal size.  A frame and wheel see such little air compared to the body which is why a skinsuit reduces so much drag compared to an aero frame and/or wheels.  Besides those two huge areas of savings, you are looking at smaller, but still valuable savings over the course of a long TT or Ironman.

The frame, helmet, pedals, shoes, and gloves all change the drag by less than 3% each, but put them all together and you can easily decrease your total drag by over 10%!  Helmets, shoes, and gloves are also relatively inexpensive compared to a new frame or skinsuit, just make sure whatever equipment you want to invest in is legal according to your local race organization or the UCI.  It’s no fun purchasing something you won’t be able to race with.

So, what is aero?  A measure of the way air moves around things that is crucial to understand in relation to cycling.  Aerodynamic drag is the number one factor that attributes to you slowing down on a bike.  In order to reduce your drag and go faster, I recommend investing in a bike fit and skinsuit first, then helmet, shoes, frame, and gloves for that extra little reduction of drag.

For more information on GC Coaching and how we can help you improve your fitness, please visit www.gaffneycyclingcoaching.com

Further Reading:

Lindsey Underwood’s thesis regarding Aerodynamics of Track Cycling

Get Faster on Flat Roads | Watts/CdA

References:
(1) Dunbar, B. (2011, June 11). What Is Aerodynamics? Retrieved December 29, 2015, from http://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-aerodynamics-k4.html
(2) Brownlie, L. 1992. Aerodynamic characteristics of sports apparel. School of Kinesiology, Simon Fraser University, Burnaby, BC, Canada
(3) Burke, E. R. 1986. Science of cycling. Human Kinetics Publishers, Champaign, Illinois, USA
(4) W. Brownlie, I. Gartshore, A. Chapman, and E. W. Banister. The aerodynamics of cycling apparel. Cycling Science, 3(3-4):44–50, 1991
(5) F. Alam, R. Brooy, A. Subic, and S. Watkins. Aerodynamics of cricket ball-an effect of seams (p70). The Engineering of Sport 7, pages 345–352, 2008
(6) L. Oggiano, O. Troynikov, I. Konopov, A. Subic, and F. Alam. Aerodynamic behaviour of single sport jersey fabrics with different roughness and cover factors. Sports Engineering, 12(1):1–12, 2009
(7) G. Gibertini, D. Grassi, C. Macchi, and G. De Bortoli. Cycling shoe aerodynamics. Sports Engineering, 12 (3):155–161, 2010
(8) M. Jermy, J. Moore, and M. Bloomfield. Translational and rotational aerodynamic drag of composite construction bicycle wheels. Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology, 222(2):91–102, 2008
(9) C. R. Kyle and D. R. Bassett Jr. The Cycling World Hour Record, chapter 7, pages 175–196. Human Kinetics, 2 edition, 2003
(10) C. R. Kyle and M. D. Weaver. Aerodynamics of human-powered vehicles. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 218(3):141–154, 2004
(11) Underwood, L., & Jermy, M. (2012). Mathematical model of track cycling: The individual pursuit. Procedia Engineering, 3217-3222

About the Author Shayne Gaffney

Shayne holds a bachelors degree in biology, is a USA Cycling Level 2 Certified Coach, USA Olympic Committee Safe Sport Certified, and a Category 3 road and cyclocross racer. He is the owner of GC Coaching and the creator and director of P2 Cycling. He can be contacted directly via info@gaffneycyclingcoaching.com

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