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Debunking The Aero Myths

  • By Caley Fretz
  • Published April 26, 2012
Photo: ITU / Janos M. Schmidt

We fight the wind, and we love it, curse it and praise it as it swirls from head to tail. It is our principal nemesis and primary ally, dooming our breakaways and providing a boost when we need it most.

We fight with resilience through this broken relationship, kowtowing to that one hidden dynamic that the uninitiated can never understand: Drafting turns cycling into chess, reversing the fortunes of the strong and crafting scenarios in which the best may not, in fact, be victorious. It is this unpredictability, brought on by an element invisible to the eye, which separates bike racing from other sports of pure endurance.

It is of little surprise, then, that an entire segment of the cycling industry has cropped up — from wheels to helmets, and much more — in singular dedication to cheating our half-loved foe of even the smallest fraction of its power.

Reluctance
Tom Boonen never used to ride aero carbon wheels at Paris-Roubaix. For his first three wins in 2005, 2008, and 2009, he was on traditional classics wheels — 32 spokes with low-profile aluminum tubular rims. This year, that changed.

“This winter, we put Tom on a bunch of wheels on the track,” explained Specialized pro team liaison Chris D’Aluisio. “We put him on some box section wheels and made him go 50kph, and he wasn’t happy. Then we put him on the deep section wheels and the difference at 50kph was just huge; we made him a believer. He’ll never ride box section wheels again.”

“He’s a convert,” agreed fellow Specialized aerodynamicist Mark Cote. Boonen made the decision to run aero Zipp 303 wheels this year, for the first time ever, and he is but one of many such recent converts in the pro peloton.

Aero gear is everywhere, because so is the wind. Sounds a bit obvious, right? And yet, it has only been in the last decade that the cycling industry and professional teams have come to the collective realization that aerodynamics has an impact on results outside of time trials.

Since the early 2000’s, the sport has seen a boom in aerodynamic wheels, helmets, road frames, and even clothing, all designed for regular road racing. The delay in some of these advancements is partially a result of recent improvements in materials and engineering. But much of the reluctance to acknowledge aerodynamic advantages comes down to simple tradition. Those barriers are now finally being torn down.

The myth of the pack
A frequent counter to the rise of aero equipment in road racing is that once nestled inside a peloton, drafting behind a bunch of other riders, the aerodynamic gains are no longer relevant.

GC riders and climbers often make this argument, citing the fact that they never have to take a turn in the wind until the final climb.

D’Aluisio runs into this perception regularly. “When I was introducing the Venge to Saxo Bank and the Schlecks, their reaction was ‘wow, that’s cool, it would be a good one-day classics bike. But I sit in the pack all the time; I don’t need it.’”

The numbers refute this view, though. First and foremost, “when you’re sitting in the group, the air speed is actually higher for the bike than for your head, because there’s less draft down there,” explained Cote. That means there’s more air hitting your equipment than your body.

The numbers show that while overall drag of bike and rider does decrease when in a peloton, any aerodynamic improvements that are present without a draft still exist.

“The percentage decrease in drag remains the same,” explained Cote. “The overall decreases, but you still get the same percentage lopped off that total drag figure.

“If you’re in clean air, going from a Tarmac SL3 with box-section wheels to a Venge with aero wheels will reduce bicycle system drag by about 6%, or 20 watts at 40kph,” says Cote. “In a draft – and we tested this in the wind tunnel with multiple riders both head-on and in an echelon – the percentage difference was still 20%. Total drag went down for the drafting rider, but the percentage decrease was still there. In the draft, you get six watts at 40kph, versus 20 watts in clean air. The gains are still there – smaller but still significant.”

The hesitancy to go aero isn’t particularly surprising. Humans can barely detect the sort of changes brought on by most aero gear – our senses in this realm are limited to variances of about 5%. And though the math doesn’t lie, it can certainly mislead.

Three-pronged attack
With the benefits of aerodynamics now established, the task becomes one of innovation and advancement.

However, replicating and measuring the precise aerodynamic forces applied to a rider in the infinite number of situations in which he may find himself is impossible. Those who test aerodynamics must therefore make assumptions, selecting the situations they believe occur most frequently or simply endeavor to remove as many situational variables as possible. To that end, the best in the industry utilize any and all tools currently available to them.

The first is wind tunnel testing, by far the most ubiquitous. The second is real-world testing, performed under a wide variety of protocols. The last is computational fluid dynamics, or CFD, which uses exceptionally complex algorithms to model airflow over a given shape. Each has its strengths and weaknesses: situations in which it is highly valuable or completely useless.

Testing equipment
In general, CFD and wind tunnel testing are the most effective for testing equipment, which is relatively static. CFD is usually used in development, and then concepts are validated in the wind tunnel. You can thank CFD for the recent rise in ultra-stable wide wheels, as well as most aero road frames and all the best time trial frames. Manufacturers can test and re-test without the enormous expense associated with hours in a wind tunnel.

“We use the wind tunnel more on stuff: products and such,” said D’Aluisio. “The repeatability is there. We also do a lot of pure component testing, and that testing is almost impossible on the track.”

Wind tunnel testing is so popular because it provides a laboratory setting that can never be found on the road. “On the road, you can’t control changes in wind, changes in temperature, changes in body position, or changes in road surfaces,” says Robby Ketchell, aerodynamicist with Garmin-Barracuda. “But you can control all those in the tunnel.”

The tunnel isn’t perfect, though. While it can control a number of important variables, there are many more that are left out completely. Cyclists and their bikes are a system, and they reside within a much larger system that includes all those variables — like drafting and position changes — that the tunnel eliminates. There are thousands of inputs that can’t be replicated in a wind tunnel, and that make it an inexact method of determining real-world gains. It can get very close, but is not perfect.

Testing athletes
When a rider is added to the equation, the test subject is no longer static. That places more emphasis on field testing. Again, engineers run up against a dilemma: The more dynamic, the less useful the lab setting of the wind tunnel becomes, yet real-world testing struggles with the inability to control major variables, like wind and rolling resistance. That’s why many manufacturers and pro teams simply use both.

“When you add a rider, and use equipment with that rider, you treat that as a system, and we do perform that testing that on a track.” D’Aluisio

The velodrome allows D’Aluisio to account for small changes in body position that only crop up under high workload.

“At 40kph, (the riders) are plenty comfortable. At 45kph, their position changes. You can watch it change. At 50kph, they’re digging. At that point, we really see how the riders look when it’s most important. You can’t get that when you only use a wind tunnel.”

Ketchell also uses field-testing regularly with his athletes. He explained that when dealing with pro riders, time constraints are always a concern. Since there simply aren’t very many good wind tunnels around, field-testing is often the only option.

“There isn’t a lot of time in pro cycling, between races and training camps and media events. It’s a logistical nightmare to get to facilities and do testing. If you go to do testing, you take away from the rider’s time to train. That’s why we have developed better ways of testing in the field.”

That includes a device he calls the “BAT box,” which measures as many of those pesky real-world variables as possible, including wind speed and direction, temperature, humidity, and barometric pressure. This data, along with power figures, allows Ketchell to calculate drag. The result is a sort of portable wind tunnel.

“I built the BAT box to use in those circumstances when we can’t get to a wind tunnel, but need to test,” says Ketchell “We can test all the riders when we go to a camp in January and create a baseline, then test them throughout the year and see how injuries or new equipment affects the system.”

“When you’re in the wind tunnel, you can’t always get a feel for how the bike rides in certain positions,” he added, echoing D’Aluisio. “With field testing, done properly, we can.”

No Perfect Solution
“Anything that you do, you need to have the appropriate protocol for testing,” says Mike Giraud, aerodynamicist with Blue bicycles and former head of the A2 wind tunnel in North Carolina. That sentiment seems to be a running theme with aero testing: While there are many ways to do it well, far more exist to do it poorly. Aerodynamicists have to take a close look at what they are hoping to gain out of a given test, which variables they can control, and which they can’t include at all.

There has to be an understanding, too, that no test is perfect. Wind tunnel testing will indeed provide an accurate and repeatable drag figure for a piece of equipment. But the tunnel can’t tell the story of interaction with all the variables found in the real world. Likewise, real-world testing can’t control all the necessary variables, making it inherently less accurate and repeatable.

Aerodynamicists must weigh these two weaknesses, and apply the correct testing methods accordingly. “Field testing has no real place in (the equipment) arena until you are down to the very end and looking to tests the products under an athlete in the real world,” says Giraud. “The truth is at this point, 99% of all your work is done, and this becomes more confirmation than anything else.”

And protocol is vital. “Your test athlete cannot also be your control athlete because every time you make a change to your test athlete, you’ve now changed your control,” says Giraud. “Having a control rider able to record all of those variables is one step closer to getting descent results.” In other words, as changes are made to a rider’s position or equipment, external variables might be changing as well. Doing the testing with a second rider, who never changes position or equipment, helps remove those variables.

Though the methods currently available may be imperfect in and of themselves, their combination does paint a highly accurate picture of the wind’s interaction with riders and their equipment. The data available (particularly third-party data like that found in our own Velo Magazine reviews) can be relied on as relatively accurate representations of the gains you will actually see in the real world. One thing is certain however: Riders not already on the aero bandwagon are only slowing themselves down.

This article was taken from our sister publication Velo News

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