LAST ISSUE WE REVEALED THE RESISTANCE FORCES AT PLAY IN THE SWIM AND HOW THEY CAN BE OVERCOME VIA THE CORRECT TECHNIQUE AND THE RIGHT GEAR. THIS ISSUE WE HEAD TO DRY LAND, TO UNDERSTAND HOW YOU CAN BEAT DRAG AND HEAT ON THE BIKE AND RUN…
WORDS JAMES WITTS IMAGE GETTY IMAGES
You’ve exited the swim, shaken yourself down, pulled yourself out of your wetsuit and are ready to conquer the bike followed by the run. That requires generating power and reducing drag on two wheels, before holding a good pace on the final leg that won’t leave you firing up like an incinerator. That might be the top line, but have you ever dug a little deeper into some of the physics and forces at play? Have you ever wondered why the faster you go, the more face-on the wind seems? Or why your tri-suit’s woven from a particular fabric? You have? Excellent news…
AERODYNAMICS MATTER
When it comes to the bike, and to a much lesser degree the run, aerodynamics count. This is one reason why: aerodynamic drag is cubic. What does that mean when seen through the prism of triathlon? Simply, that doubling your bike speed requires eight times as much power; in other words, the faster you go, the greater the air resistance. It’s why air resistance rather than friction, like from rolling resistance of your tyres, takes over as the dominant factor holding you back once you’re riding above around 16km/hr.
A large cross-sectional area is also a large detriment to your new PB, an increased area resulting in an increased amount of air resistance. Place your hand out the car window on your next drive. Rotate it between the vertical and the horizontal and you’ll see what we mean. This aerodynamic drag is quantifiable as it’s the resistance attributed to an object and one given the term CdA. This is an abbreviation for the co-efficient of drag. It’s a dimensionless number that’s the result of a body’s drag size, shape and surface texture. CdA ranges upwards of zero. Physics dictates that an object with a drag co-efficient 0 can’t exist. Something that’s very much real are teardrop-shaped bars, which can register a figure of 0.005. That’s aero. A brick might be 2.0. Not surprisingly, that’s not aero. CdA examples of elites using aero-shaped bars might come in at the 0.18-0.25 mark. For a good amateur triathlete, that’d be more like 0.25-0.30.
“The aim is to deliver a good CdA but one that you can hold.” Those are the words of David McNamee, one of the greatest long-course male athletes this country’s produced, his list of achievements including two third spots at Ironman Hawaii (2017 a
