(This article originally appeared in the April 2014 issue of Road Bike Action Magazine.)
By Michael White
The wind tunnel is now obsolete. At least, that’s what the folks at Alphamantis Technologies would have you believe. The Montreal, Canada-based company has been developing its Track Aero System since 2011, a technology that allows for heretofore-unseen bicycle aerodynamic testing in the near real-world riding conditions of a velodrome. At a recent collaborative event held at the Velo Sports Center (located on the grounds of the StubHub Center athletic complex in Carson, California), technicians from Alphamantis, plus a collection of top bike fitters from Retul and a crowd of professional riders, doctors and coaches, all gathered to partake in two days of aero testing and analysis.
Part bike-fit clinic and part science experiment, the event’s purpose was to illus- trate the growing significance of aerodynamic optimization for bike fits while showcasing the technology that may supplant the wind tunnel as the optimum form of aerody- namic testing for bicycles. Here’s what we discovered.
WIND TUNNEL SHORTCOMINGS
“Wind-tunnel testing can be contro- versial when it comes to whether or not you subtract off the effect of the fork and rear mounts [that hold the bike in place] from the overall measured aerodynamics,” says Andy Froncioni, who holds a PhD in aerospace and mechani- cal engineering and serves as chief technology officer at Alphamantis. “But the wind tunnel’s main disadvantage is that real riding involves a lot of dynamic interaction between the rider and the bike. There’s a lot of lean steer happening, and there’s an incredible amount of aerodynamics associated with it, so moving things, like on the track, will test differently than various stationary things.”
“The main disadvantage with wind- tunnel testing is that you’re locked into place, so you don’t have the freedom of movement that you would on the road,” agrees Todd Carver, cofounder of Retul. “Measuring cycling aerodynamics is different than measuring aerodynamics for other vehicles like cars or airplanes. Those are pretty static objects. A cyclist’s body, and thus the overall shape of the combination of a bike and rider, is moving. So when you take that variable out of the drag equation, it’s really just not as realistic. What that means is that a lot of times in wind- tunnel situations you fit people into body positions that are sustainable in the tunnels because the bike is locked into place with both front- and rear-wheel mounts. But, you put that rider out on the road where he must spend energy to steer and control the bike and that’s where everything can fall apart.”
GENESIS IN BOULDER
For the purposes of cycling applica- tions, aerodynamics can be simplified as how efficiently one converts power into speed. And in the most fundamental terms, aerodynamic testing, be it in a wind tunnel or otherwise, measures an object’s coefficient of drag, or CdA, which quantifies the resistance of an object traveling through a fluid environ- ment, such as air. The smaller the CdA number, the less resistance an object experiences, and thus the faster it can travel with all other elements being equal.
“What’s being done here at this event is determining CdA by measuring the power required to go a certain velocity,” says Dr. Allen Lim, cycling training guru and founder of Skratch Labs nutrition products, who attended the Retul event to help shed some light on the science being conducted. Lim, together with Retul’s Todd Carver, had previously experimented with outdoor aerodynamic testing in their hometown of Boulder, Colorado, starting back in 1999.
“Wind tunnels are very good for select comparisons, but we started abandoning them because they didn’t give us a lot of insight into what was happening with the athletes,” continues Lim. “And, the outdoor testing was difficult to say the least, because we had to seek out the straightest, flattest roads possible. We all had to wake up early and conduct our testing around 8 a.m., because that’s when we would find conditions with the least wind. By isolating all of the various elements that go into riding a bike, we were able to, with varying degrees of success, measure the aerodynamic drag a rider experiences while pedaling down a road.”
In an article published in the May 2011 edition of the American College of Sports Medicine’s journal, Medicine & Science in Sports & Exercise, Lim and Carver, along with their colleagues, concluded that, among other things, “[…] power meters are sufficiently precise to distinguish the effects of body position and tire infla- tion pressure on measures of aerody- namic and rolling characteristics,” and that their method of testing “[…] should help coaches, athletes, and scientists to better predict road cycling performance.”
THE NEXT LEVEL
Utilizing a complex series of algo- rithms in conjunction with the con- trolled environment of a velodrome, Alphamantis’ technology has taken Lim’s and Carver’s work into a more sophisticated realm of isolating the measurement of aerodynamic drag (CdA). But for all of its complexities, the system is comprised of a relatively simple set of components. Bikes must be fitted with both a power meter and a non-GPS-based speed sensor, while the rider wears a mobile-phone-sized ANT+ to WiFi repeater developed by Alphamantis, which helps collect and transmit data to the observer. Because data gleaned from the velodrome is easier to analyze when broken up into segmented laps, Alphamantis developed its own wireless timing sys- tem, which has the added benefit of validating the numbers recorded by the speed sensor. Finally, to put everything together, all of the math and physics equations are coded into proprietary, real-time data-crunching software and analyzed trackside with laptops.
In addition to the Velo Sports Center, the Alphamantis system can be found at velodromes in Ballerup, Denmark, and Sydney, Australia. For the collaborative Retul event, Alphamantis also brought in represen- tatives from a soon-to-be-completed velodrome in Hong Kong, as well as a venue in Perth, Australia, with an eye toward incorporating its system at those sites in the near future.
PUTTING IT TO THE TEST
To demonstrate the Track Aero System’s abilities to the assembled group of Retul fitters at the Velo Sports Center, Alphamantis organized three distinct tests: one that would measure the aerodynamic drag effects of riding position, one that would measure the effects of various drafting situations, and one that would compare the effects of various cycling helmets. RBA contributor Dr. Johnathan Edwards served as the guinea pig for the riding position and drafting tests. This saw him first receive an evaluation from the Retul fitters of his road position on his personal bike, and then saw him receive what the Retul fitters described as a “modified triathlon position,” which included replacing his Fizik Arione saddle for an ISM Adamo model, and adding a set of clip-on aero bars.
Next, Dr. Edwards was put on the track in the “modified triathlon” setup and recorded an average CdA of 0.257. After adjusting his bike back into his standard road setup, he put in more laps on the track while riding on the hoods and recorded an average CdA of 0.295. That 0.038 difference in CdA equates roughly to a savings of 2 minutes and 32 seconds (at 30 mph) over a 40-kilometer time trial. Hardly a surprise, the results of this test illustrated the effectiveness of a lower body position coupled with aero bar extensions—there’s a reason why it’s the preferred setup for time trials!
For the drafting test, Dr. Edwards remained in his regular road position, hands on hoods, and was joined on the track by Nate Koch, a top U.S. pro track racer. Riding at a constant velocity just behind Koch, Dr. Edwards recorded an average CdA of 0.200. This was a CdA of 0.095 lower than riding alone, resulting in a savings of 95 watts when riding at 30 mph. Next, Dr. Edwards and Koch rode side by side, which yielded some surprising results. Dr. Edwards recorded an average CdA of 0.324, or 0.029 higher than riding alone.
“Side-by-side riding doesn’t have the cyclists share any of the low-pressure region behind each rider,” explains Froncioni. “Each individual has his own low-pressure zone pulling him back- wards. In addition, the flow of air is forced around a wider frontal area, which leads to an even bigger low pressure zone behind them.” The take- aways from these tests? Aero bars are beneficial, drafting behind someone is effective, and riding side by side will slow both cyclists down.
While these results were hardly surprising, these tests demonstrated the Alphamantis system’s ability to collect and confirm consistent and accurate known data. On day two of the event, we would move on to another series of tests that would better demonstrate its potential to measure aerodynamic efficiency for cyclist-specific, real-world riding scenarios in the form of equipment choices.
For the event’s final demonstration, Alphamantis brought in Missy Erickson, one of the top female track sprinters in the U.S., to test the aerodynamics of a variety of helmets. Erickson was chosen for her experience on the track, consis- tency in her pacing and ability to main- tain a consistent and stable riding posi- tion. Here are the results of our test, with Missy riding her track bike fitted with an ENVE SES Aero bar:
For Missy’s riding position, it was concluded that the four standard road helmets—Specialized Prevail, Bell Gage, Giro Aeon and Louis Garneau Course— were close enough in aerodynamic efficiency to each other as to render their differences relatively insignificant. Other factors like fit, comfort, ventilation and weight would therefore come into play if Missy were forced to choose which helmet to use on a permanent basis. Similarly, the two aero-road helmets—Giro Air Attack and Specialized Evade—were likewise close enough in aerodynamic efficiency that it would suit Missy best to consider the helmets’ other characteristics if she were forced to choose between the two. What is noteworthy, however, is that the aero-road lids offer a significant aerody- namic advantage over the standard road models—between 0.006 and 0.010 lower CdA, which equates to a savings of between 6 and 11 watts depending on the specific helmet.
We also pitted Missy’s personal Giro Selector and Advantage time-trial helmets against one another, along with the POC Tempor time-trial helmet. For Missy, both of the Giro models produced the same CdA of 0.223 as one another, while riding with the POC Tempor resulted in a CdA of 0.227. At least that was until we placed cellophane tape over the Tempor’s large front vents. This experiment brought the Tempor’s CdA down to the same as the two Giro models for Missy’s position.
NOT THE WHOLE STORY
If you were shopping for the most aerodynamic road helmet on the market, then you might look at our data and conclude that the Specialized Evade is the helmet for you. However, our testing is only the tip of the iceberg when it comes to the featured helmets’ aerodynamic efficiency and says nothing of their other attributes, such as fit, comfort and ventilation.
“What’s aero for one athlete might not be aero for another,” says Jim Manton, owner of ERO Sports, Retul- certified fitter to several professional road cyclists and triathletes and head of aerodynamic testing at the Velo Sports Center. After months of aerody- namic testing on a wide variety of athletes using the Alphamantis system, the most significant thing that Manton and his team have learned is that there are no constants. Concerning helmets, for example, arm position, back angle and head movements can all have dramatic effects on their aerodynamic efficiency. Consider this: in a previous test, separate from ours, a test rider with a higher back angle than Missy’s rode with the Louis Garneau Course and Giro Air Attack helmets, yielding CdA numbers of 0.262 and 0.268, respectively. So for this rider, the more aerodynamic option was the Course, whereas for Missy the more aero option was the Air Attack.
SO WHAT’S IT ALL MEAN?
The Alphamantis system is an impressive advancement in aerodynamic testing technology, most notably because of its ability to quantify data in a manner that cannot be duplicated in a wind tunnel, with a rider interacting with his or her bike and pedaling through space, just as they would in the real world. But it’s not without its drawbacks.
“Wind tunnels are really better for aerodynamic testing at non-zero yaw angles,” concedes Froncioni. “They are also better suited for testing individual components like wheels, for example, for product development.” This is because countless individual riders will utilize said product design with their own unique aerodynamic characteristics based on their body type, riding position and other equipment choices.
More than anything, our experience at the Velo Sports Center taught us that when it comes to cycling, aerodynamics is a highly conditional—rather than definitive—concept. It’s one that varies from athlete to athlete, bike to bike and product to product, becoming another vital piece of the total performance puzzle. So whether it’s inside a wind tunnel or at a velodrome with the Alphamantis Track Aero System, the future of cycling lies in aerodynamic testing. As Dr. Allen Lim concludes:
“Being able to optimize drag is a lot more meaningful than many of the phys- iological elements VO2 max, thermal regulation—because there’s no combi- nation of factors that affect an athlete’s performance output like aerodynamic drag. The longer the race, the more relevant aerodynamic drag becomes, because it’s all about saving energy.”
A two-hour testing session at the Velo Sports Center starts at $449, while a three-hour test starts at $599, both of which include a Retul 3D motion- capture analysis of the customer’s fit before any testing begins.