In his article about cadence our expert Andrés Díaz explained the basics about finding the optimal cadence. Today Andrés gives us a short introduction into aerodynamics and the aerodynamic balance and a few tips to gain some watts.
Learning from Formula One
In aerodynamics there is an important concept called Center of Pressure (CP) which is not very well known. This might be because it is highly technical. Motor sports enthusiasts will be more familiar with this term, since it is the cause of understeering and oversteering. In this article we will make at easy and understandable and explain how you can profit from understanding this concept.
Aerodynamic balance on the bike
On a bike the front wheel has the biggest influence on handling and control, mainly because of the steering axle: the fork. As triathletes, time trialists and road cyclists our main goal in windy conditions is to make our bike more stable and easy to control. Therefore we want our Center of Pressure to be located as far back as possible. This allows us to maintain our aerodynamic position for longer period of time.
But how do we manage to move the CP backwards?
Well, the easiest way is to use a rear wheel with the largest rim depth possible. Although this might sound like the exact opposite of getting a more stable bike: using a rear wheel with the largest rim depth possible will make the bike easier to handle. As a consequence we can stay in an aerodynamic position for a longer time and this makes us faster. This is the main goal of optimizing the aerodynamic balance.
Choosing the best wheelset
When riding a bicycle, the main cause of aerodynamic drag is our own body. It makes up for about 80% of the total aerodynamic drag. The remaining 20% are made by the bike and its parts i.e. frame, handlebar and wheels. On paper a 90mm depth wheel is faster than a 60mm depth wheel but if you are not able to control the 90mm wheel and pedal in your aero position you will be losing all the aerodynamic benefit of the wheel. The difference between using a medium rim depth wheel (i.e. 60mm) and a high-profile wheel (i.e. 90mm) can be between 5 to 15 watts (in favor of the largest rim depth wheel). However, the difference between pedaling in an aero position on a TT bike or grabbing the base bar can be more than 50-70w. On a road bike the difference between riding with your hands on the hoods or in the drops is not as big but still makes a big difference.
What makes you faster:
Use a rear wheel with the largest rim depth you can.
Use a front wheel with the largest rim depth you can control.
Pedal in your aero position as much as possible.
Use the combination of wheels with which you will race as often as possible, not only in competition.