Why aerodynamics is important to cycling

After decades of cyclists being weight weenies, cyclists are now at least as focused on aerodynamics. Why the change? Not much about bikes or the air changed, but athletes and bike manufacturers started going into the wind tunnel in the ‘90s, and with that our ability to significantly effect aerodynamics changed. It took another 10 years before anyone outside of triathlon or time trials noticed, but now anyone buying a bike has to consider whether they want the lightweight bike or the aero bike. If you want a more complete history Michael Hutchinson wrote a great article about the history here

Where your power goes

Whether or not you use a power meter, the goal of nearly all training routines is to increase power output. In fact it’s probably fair to say you can break down most cyclist’s activities into two categories; 1) training in order to increase power, 2) buying better equipment in order to increase efficiency. So if we look at it in that way, where’s the best place to spend money? The plot below breaks it down.

On a flat road roughly 90% of the forces holding you back come from aerodynamic drag. As you train, and increase your power output, aerodynamics gets even more important. In terms of power, if you’re pedalling at 250 Watts, 218 Watts is going to overcome aerodynamic drag.

That’s pretty astonishing! If you’re considering buying the best chain and you think it will make your drivetrain 20% more efficient that’s a 1.5 watt savings. That’s equivalent to less than a 1% improvement in aerodynamics. You’re almost always better off getting a slightly more aero helmet, or simply taking the time to clean up your brake/shift cables. Of course, if you have the money you should do both!

Hills

Yes but what about weight? Cyclists weren’t weight weenies for decades without some good reason where they? No, weight is still a critical factor, especially in mass start races or group rides. When a race finishes on a hill, or getting dropped on a climb means you’re no longer with the pack, weight is king. But if you’re in a breakaway, triathlon, or time trial then it takes a significant hill to make weight matter. In general your speed drops low enough to discount aerodynamics when the gradient hits somewhere between 5-8%, depending on how powerful a rider you are.

Conditions vs. Time

The importance of aerodynamics is partially the reason training with power is so useful. Wind and air density changes mean your time on a particular route often vary more with weather changes than they do with changes in your fitness. Anyone who’s every repeatedly tried for a Strava KOM knows that feeling. A tailwind helps of course, but the difference between a bright, sunny day and a warm, overcast day can change air density enough to make the difference as well. I do aero testing at the Preston Park velodrome, which is outdoor, and it’s amazing how much these parameters can change, even over 30 minutes or less. The first time I saw this become a casual cycling topic was in the runup to Bradley Wiggins hour record attempt They calculated that favourable weather conditions could add almost 1 km to his final distance, and that was for an indoor velodrome! http://www.cyclingnews.com/news/air-pressure-and-track-skills-will-be-vital-for-wiggins-hour-record/

What does all this mean for anyone trying to go faster? Well, for now it’s obvious that we should all be focusing on aerodynamics. Fortunately the cycling media is doing more and more reporting on this, and wind tunnel data for various components is almost easy to find now. Still, with things like training advice we can read other’s advice and then try it out to see if our LT or VO2 max has improved as promised. We’re still missing that feedback loop with aerodynamics. Even at the pro level opportunities to test aerodynamics are only a few times a year.

More on this next time!

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