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What’s REALLY the most effective way of measuring cycling aerodynamics?

Image Credit: © Danny Gys Photo & video

One of the reasons that cycling aerodynamics can be so difficult to get to grips with is that the various ways you can measure them often don’t completely agree with each other. Different methods and protocols suit different purposes, budgets and levels of expertise.

So even if you want to take the matter a bit more seriously than just guessing, you have choices to make about your method, how much you’re going to spend in terms of money and time, and how accurate you want the result to be.

I thought it might be interesting to take a quick tour.

Wind tunnels are often taken as the “gold-standard” for aero-testing. They probably aren’t, but only because there’s not really a “gold-standard” in this area at all. The main advantage to a wind tunnel is that it can measure very, very accurately. If you stick to the same tunnel each time, the results are usually highly consistent from session to session.

The biggest problem is that the thing they measure so accurately and consistently it isn’t always very representative of the real world. It’s fine if you’re looking at hardware like frames or wheels. But if you’re looking at rider position, it’s on a bolted-down bike, the rider probably pedalling at a fairly low intensity, and not having to deal with riding in the real world, in real conditions.

In a tunnel, for example, you don’t have to look where you’re going, you can hang on the front of the saddle with no risk of being bounced off by a rough road and you can achieve contortions that are impossible to sustain under full power. It’s easier than you’d expect to perfect a tunnel position that is practically useless in real-world cycling.

There are also choices to make about the speeds you’re going to test at, and what angle of yaw (crosswind) you want to find out about. So while you can measure very accurately, you quickly run into doubts about what it exactly is that you’re measuring, and how it relates to life outside the tunnel. Across the whole industry, tunnels are still very important, but they’re becoming a little less so for testing riding positions, suits and helmets.

At the moment, the main alternative to tunnel testing is track testing. You ride a few laps of a (usually indoor) track at a representative speed while your power and speed are recorded and processed through some software that corrects for the geometry of the track and produces a CdA (drag) number; just as in the tunnel.

More advanced ways of doing this will measure your speed through the air as well as over the track, since even a solo rider will start to stir the air in the track and create a slight vortex effect, meaning the air speed is a little lower than the ground speed.

It’s not quite as accurate as a wind tunnel. There’s more noise in the system, the slight air currents that are inevitable in a large open building will have an influence, and you’re ultimate