Aerodynamics 101

While training for Ironman Canada last year, I spent some time working with some of the best aero experts in the business to uncover some of the intracies of aerodynamics. The result? I wrote the article below about aerodynamics for the Vision Quest newsletter.

Well I spent some – actually a ton of – time in the wind tunnel this past week with VQ aero expert Jim Sauls and the King of Aero himself, Steve Hed.  Steve is one who lets the results speak for themselves.  He was the one who dialed in Lance Armstrong’s aero position for the last six tours and he’s spent the last three years working with Levi Leipheimer and the top triathlete in the world.  Not to mention he and his wife also have personal experience with Ironman racing! We also brought along VQ’er Bob weeks, an MIT grad who added great insight to the project.  With all this brain power (Jim, Steve and Bob’s brain power, not mine!) I knew the fancy words and complicated equations wouldn’t take long to overwhelm me, in reality it only took about 10 seconds until I was lost.  Reynolds numbers, drag coefficients, lenticular designs, boundary layers, K-factors and every other imaginable term were being thrown around constantly and we joked that we needed to get a helmet made of ice for all the experts to keep their heads from overheating.  All these guys were great to work with and the time I spent with them and Mike Giraud at the A2 tunnel was some of the most productive and educational time I have had as a coach.

We went into the tunnel with a few simple goals:

1) To verify the data that Jim and I have collected on ourselves using Jim’s aerodynamic expertise and my practical knowledge and experience.  Jim has done over 100 runs at the track and has great data using a wind meter, power meter and speedometer, along with a complicated equation he developed. A long career in pro cycling and work with Floyd Landis in the wind tunnel has given me a few insights as well.  The biggest challenge at the track was accurately determining wind speed and wind direction, along with consistent speed.  Jim has accounted for this variability in his equation, but with the 160 tunnel runs that we have just completed, we will be able to tweak the equation even further to make it more reliable.  The cool thing is that all this time in the tunnel has showed us we weren’t far off with our initial equation.  When the few changes are made, the track protocol will actually be more practical than wind tunnel testing because it more closely mimics real world riding.  First objective down!

2) To learn more about the intricacies of aerodynamics for half and full Ironman racing.  We used Steve Hed’s experience and me as a guinea pig since I will be doing Ironman Canada this year.  Steve explained to me a very common-sensical yet brilliant concept that success in a 112 mile TT would require multiple aero positions.  I would need a super fast position for riding 22-28 mph (not very often), another for typical race pace riding in the 18-22 mph range, and a third for slow climbing speeds at 10-18 mph.  With three fast positions instead of just one, I can switch my positions based on current speed and demands of the course.  All three positions are relatively fast and aero, but some will allow me to produce power more effectively depending on given situations.

3) Learn what effects different types of adjustments actually have on comfort and aerodynamic drag.  Some small changes can result in much greater comfort without significantly changing the drag coefficient.  Altering my wrist and forearm angles were a huge factor in my overall comfort but ultimately had a pretty small effect on drag.  The bottom line is you have to experiment to find what works, just because you saw a pro rider make a certain change doesn’t mean the same will work for you.  For example, we found that when Jim brought his elbows in, his shoulder width decreased dramatically and significantly reduced his frontal drag.  When I made the same change, my drag numbers did not change, but I was definitely a lot less comfortable.  This really illustrates the point that people react differently to the same changes and unless you pay attention to the effect that the changes have on riding speed and sustained power and comfort, you may actually be hurting yourself rather than helping.  For those racing the full Ironman distance, and to a lesser extent the ½ Ironman racers, comfort probably trumps aerodynamics to a certain degree, and just because a position is fast, doesn’t mean it will be fast on race day if you can’t be comfortable enough to maintain the position.

We did all our trials with 7 degree yaw angle (the fancy term for crosswind) because this is the most commonly encountered drag angle faced in the real world.  Wheels, positions and speed are highly variable as wind angle and wind speed fluctuate.  Most companies test their equipment and positions at zero degrees. This can give some nice low drag numbers, but doesn’t turn out to be very practical since the wind is seldom directly in your face.

I can now tell you from this experience that there are a lot of claims out there about bikes, helmets, wheels and all manner of other equipment, but these companies can manipulate the test data to show the results they want.  It might be right for one rider on the right course in the right conditions but I can tell you that it just isn’t possible for one piece of equipment or position to be effective for all riders and all conditions.

We did all our trials with 7 degree yaw angle (the fancy term for crosswind) because this is the most commonly encountered drag angle faced in the real world.  Wheels, positions and speed are highly variable as wind angle and wind speed fluctuate.  Most companies test their equipment and positions at zero degrees. This can give some nice low drag numbers, but doesn’t turn out to be very practical since the wind is seldom directly in your face.

Most people get it wrong, even the really good ones miss out on a lot of time because they ride in a position they think is fast but have never actually evaluated it to see if it truly is.  A lot of people ride TT bikes that look really cool, but actually carry no real aerodynamic advantage, at the same time they often carry an additional weight penalty.  Some companies seem to think if they just put an aero shaped tube in every conceivable location, then the bike will be fast just because it “looks fast.” A well set up road bike with aerobars can easily be faster than many TT bikes when you look at pure power savings.  Those athletes who are really consistently fast have become that way because they have spent the time and the money working in the wind tunnel to make changes and having the data to back them up.

What I really took away from this experience is that any time you’re in a time trial situation, whether it be for 20k or 200k, time spent optimizing your aerodynamic position is well spent.  Even at the relatively low speeds of Ironman distance racing, aerodynamics play a huge role, much more than I ever thought (more on this to come).  So before you just head out and start making all kinds of changes to your position and buying fancy new bars and wheels, think about setting up an appointment at the track to see how your current position is and learning what changes can make a real difference.

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