The Principles of an Aerodynamic Bike Fit

Riding a bike down the road can be very simple. The sensation of air moving around the body or climbing a hill can have very profound effects on how a person will perceive their world after they get done with their ride. Generally as a person transforms themselves from average rider to an athlete, they begin to get a more complicated perspective of how a bike can travel down the road as well as how their body responds to the bike.

Manufacturers are continually developing products that allow cyclists to be more efficient on the bike. However, some of these products work great for some people and not so well for others. As a fitter, we have to be able to see past the advertising claims and use what works best for each individual athlete.

When it comes to fitting an athlete for an aerodynamic position, there are many myths out there on what makes a person more aero. One of the myths is that a person loses power to the pedal when they become more aero. Allowing an athlete to produce high power and be very slippery in the wind is achievable—that is one thing we focus on when we optimize athletes in our wind tunnel. To achieve the balance between being aero and having optimized power, biomechanics, biometrics, and comfort we have to start with a solid foundation.

More: 6 Easy Ways to Get More Aero

A Solid Foundation

Let's start with the feet and sit bones. A rider that has a weak foundation for their sit bones and feet will be limited by how aero they can get. When we are looking at a rider's foundation, we are mainly trying to keep the body in a neutral position. If a rider has a high arch, varus or valgus feet, or if there is a leg length discrepancy, appropriate steps need to be taken so a rider can sit naturally on a bike.

We don't want to push a rider into a position they can't sustain! We want a rider to fall easily into an aero position, and as they do this, they will be able to hold it for a much longer period of time.

Along with the feet, we also do this by looking at their saddle and choosing a saddle that supports their body. By providing a solid foundation for the rider, their comfort on the bike will also improve. In addition, if their current bike geometry is not ideal, they will also be limited on power production and holding a tight aero shape for long periods of time.

Here is a before and after photo of Cheryl, an avid triathlete whose foundation was not ideal. This triathlete is very petite, and like many petite athletes, selecting a bike with the right geometry and without having to use 650c wheels can be very challenging.

And this is the final result with a properly fitting bike and an ideal foundation.

More: 5 Things I Learned in the Wind Tunnel

Because of her body proportions, Cheryl was a great candidate for a custom bike. After her new bike arrived, she was able to hold her body in a better aero position. The results were very dramatic—with a 261-gram drag reduction! That equates to 2.6 seconds per kilometer...in an Ironman, that would be 7:48 faster. In addition to an aero advantage, she had more power to the pedal and was much more comfortable on her bike, allowing her to sustain this position on the road. Cheryl was able to get her torso much lower while keeping her hip angle open.

When we do aerodynamic testing, we also look at helmet options, wheels and where to place nutrition and hydration on the bike. Depending on the rider and how they react to the equipment in the wind flow, we can then start to select wheels, clothing, and helmets that are best suited for them. Many times we have found unconventional ways of making athletes faster.

Another great example of the effects of a proper fit and solid foundation is an Ironman athlete, Susan. We tested Susan in the wind tunnel before making any changes to her position. After going through a full fit using our 3D system, we returned to the wind tunnel for more testing.

What we found was that her position was completely hindering her performance and power but also causing her legs to be more fatigued for the run. As running was Susan's strength, we wanted to assure that her running muscles were less fatigued, allowing her to have a better run in her next Ironman. The body positional changes that we made with Susan led to a reduction of 463 grams of drag and saved her 13:53 on her next Ironman.

More: On the Bike: Fit Versus Technique

Body Position

One of the big hurdles that many amateur and pro athletes must overcome is how to hold their body's position during their triathlon or time trial. For some triathletes, they will become more aero (as much as 250 grams!) by flattening their back and turtling their head. Others are better off keeping the head in-line with their back. It all depends on how the rider can hold themselves on their bike and the surface area of the athlete.

The picture of Ted below shows a before and after where he was able to flatten his back and lose another 250-plus grams of drag. (That's 2.5 seconds per kilometer!)

More: 10 Bike Fit Myths...Debunked

Aerodynamics = Unique to Each Person

Just like bike fits are unique to each individual, aerodynamics is also unique to each person. Some people try to become more aerodynamic by purchasing a new aero bike, wheels, or a new helmet. What we have found from testing many athletes is that a solid foundation from a good bike fit can make you more aero than new equipment.

A new bike may cost you $4,500 for a 200 grams of drag reduction (about $22.50 per gram of drag). A new set of carbon aero wheels will cost you around $3,200 for 150 grams of drag reduction (about $21.33 per gram of drag). Getting a comprehensive optimization (bike fit and wind tunnel test) will cost you around $750, but can save you 350 grams of drag ($2.14 per gram of drag).

After you have a great aero position, now add in the aero equipment and you have yourself a very big competitive advantage! If you are like Cheryl above, you may need a different bike to get you in that ideal position, however many people overlook the importance of having a solid foundation and a good bike fit when it comes to an aerodynamic optimization.

More: Which Aero Equipment Offers the Most Benefits?

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