Wind Tunnel Testing, Virtual Wind Tunnel & Weight vs. Aero.

Aerodynamics 101

You’ve got questions, we’ve got answers…

Howdy Tech Support from the great state of Texas. It seems like more and more products are being wind tunnel tested, yet multiple companies often claim that their product is the most aero. They can’t all be right in their claims. What gives?

Lincoln, TX

Dear Lincoln,

You have hit upon one of the great mysteries of the cycling world – how can so many things be the best? While wind tunnel testing has helped excel product development and improve performance, it has also often led to a significant amount of confusion as the test results can vary significantly in both concrete terms, as well as through interpretation.

In some ways, all the companies can be “right” in their claims. Under certain conditions they did likely achieve the results and it was likely the “best in test”. However, “best in test” may not mean much to your performance if the results do not translate well to the real world and your individual circumstances. Trying to boil aerodynamics and its relationship to performance down to this simple a level attempts to overly simplify a complicated subject that humans are still far from mastering.

From the yaw angle (angle that the wind hits the object), to the fixtures that hold the bike, and the wind speed used in the test, there is not a standardized test protocol for aerodynamic testing in the industry. Every test is thus its own entity and the results depend directly on the protocols used. Also, unless you are the test subject, none of the tests take the biggest aerodynamic variable into account – you. Each rider is shaped uniquely and has their own posture and technique when riding. For this reason, the helmet, frame, handlebar or other component that tests best under the test subject may or may not be the one that would work best for you.

Wind tunnel data, and continued development of aerodynamic computer modeling, will continue to provide useful information that helps with product development and helping make cyclists faster. However, it is important to realize that aerodynamics is a very personal and individualized concept; what works ideally for one rider or in a specified condition may not translate to working ideally for you. Do not choose your riding equipment based on wind tunnel data alone. Instead, consider the big picture and make sure the products you choose helps you stay as aerodynamic as possible without compromising power and comfort in the process.

IB

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While I would very much like to go to a wind tunnel, I just can’t spend the dollars. Is there any way to accurately test aerodynamics without a wind tunnel?

Tom C., via e-mail

The short answer is “Yes.”

Researchers at the University of Utah, headed by Jim Martin, PhD, developed and scientifically verified an aerodynamics testing formula that consistently and accurately predicts aerodynamic drag. The results from these protocols are arguably even more valuable than the data a wind tunnel provides, as the results are in real world conditions. While it does takes some initial study of the procedure and equipment, the procedures are not difficult, are repeatable and scalable test to test, and provide very functional data. www.sportsci.org/2006/jcm.pdf is a link to a complete list of required items and instructions on the protocols to use and www.sportsci.org/2006/CdA_calculator.xls is a link to the associated spreadsheet for data recording and calculations. You need a power meter to complete the tests.

While you can do these tests on your own, it is easier to do it as a group and to test multiple people at once. In addition to the peer reviewed scientific proof provided by the Utah development team, we have anecdotal evidence that the formula works as well. Dean Phillips, one of our lead bike fitters, has used this formula to personally test a wide variety of equipment and riding positions for himself. Even though his training hours are down from three years ago, he has dropped almost three minutes of time off his 40K and broken many regional TT times, some that were set by pro riders over a decade ago, using the data he has gathered.

IB

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How much does shaving weight on the bike really matter? As a follow up, what about becoming more aero? Are there any averages that can be used?

Trish, NY

The weight versus aerodynamics question is likely as old as the first bicycle race. Based on the work that provided the formula referenced above (Martin et al.), there is some excellent data on just how much different variables matter and what they will get you.

Some interesting statistics based on an average TT course and rider:

Reducing Weight: A 2% reduction in total vehicle weight (bike and rider) results in about 6 seconds of time savings over a flat 40K. If you and your bike weigh 180lbs together, this means you would need to take a huge 3.6lbs of weight off your bike to see this benefit. Most riders would have an easier time taking this amount of weight off their body. Interestingly, if you reduce weight by 2%, but also reduce power by 2% simultaneously, you will go about 13 seconds slower. So, no matter how light you can run your body, don’t lose power in the process or you will go slower.

Reducing Drag: A 2% reduction in overall drag results in about 12 fewer seconds to cover the same 40K. If you are willing to work at it, many riders could see 10-20% improvements in drag, which means a couple minutes.

What does this mean? It means for a fit athlete, you want a reasonably light bike, but realize that gram counting rarely pays off and that continuing to work on maximizing the potential of your maintainable aero position and equipment is where you will see the biggest speed gains.

Ride hard and smart.

Ian

Ian Buchanan is co-owner of Fit Werx. Fit Werx has locations in Waitsfield, VT and Peabody, MA and offers cycling and triathlon products, specialty bicycle fitting and analysis services, consultation, and technology research. Fit Werx can be reached in VT at (802)496-7570, in MA at (978)532-7348 or through the Web at www.fitwerx.com.