Well then, how do you measure the aerodynamics of a rider?
Well then, how do you measure the aerodynamics of a rider?
Well, this comes down to your frontal area. And, as you can imagine, it’s not basic mathematics and physics to figure this out.
“The equation for drag is drag = 1/2 x rho x velocity2 x drag coefficient x frontal area [rho being air density]. Often the most difficult part to measure in that is frontal area because it usually requires a front-on photograph, the correct scaling factor (wheel diameter is often a good way to estimate) and then some software to give a value. To simplify matters the drag coefficient and frontal area are often combined to give a CDA value which can then be used to compare positions, equipment configurations and so on.”
So it’s nice and easy then. And there are plenty of variable to change on a bike – especially so on a TT bike – that can make a notable difference to the CDA number and all have to be factored into the equation. “Changing the number of stem spacers, changing seat height and position, altering bar position and changing the separation/position of aerobars/extensions can have a considerable impact on the drag by improving the aerodynamics of the rider’s position,” he offers.
“Simple things like clothing fit are also often overlooked. Anything that flaps around will always be bad and so a well-fitted skinsuit will always beat a loose jersey. Even aero helmets can be detrimental if you don’t take account of their shape and how they fit relative to your shoulders and back.
“It should also be remembered that whatever you find in the wind tunnel needs to be maintained when out training. Being able to maintain a good aero position over the duration of an event takes time and perseverance while potentially training off the bike to improve flexibility as well.”