Aerodynamics

(Originally published in the Sept. 30 to Oct. 6, 2012 issue of the Baguio Chronicle ---

a weekly newspaper based in Baguio City, Philippines ---

by Sly L. Quintos, Associate Editor.)

EVERY cyclist who has pedaled into a stiff headwind knows about wind resistance. It's exhausting! And in order to move forward, the cyclist must push through the mass of air in front of him. This takes a lot of energy.

Overcoming air resistance is every cyclist’s mission. Cyclists (racers and commuters alike) are aware of this problem and over the years have developed riding techniques and bicycle designs for reducing it.

Experts say that a cyclist accounts for 65 to 80 percent of the drag (wind resistance) while the rest is attributable to the bicycle design and properties. This is because the human body is simply not well designed to slice through the air. 

Most recreational bicycles in which the rider sits up have very poor aerodynamics and where air resistance is therefore at its highest. Aerodynamics is easily defined as the branch of fluid dynamics concerned with the study of gas or air flows which involves calculations of velocity, pressure, density, and temperature. 

In cycling and in bicycle design, improved aerodynamics aims to increase or attain the desired speed at the least effort (force or energy) spent. By reducing the drag by even 1 percent, experts believe, a rider can possibly gain more than a five-foot advantage for every mile at 30 mph.

The rider's position is very important to the overall aerodynamics of both the bicycle and rider. Researchers have shown that proper body position can reduce drag by 30 percent over an upright riding position. 

The most aerodynamic position is obtained by using the hill-descent position where the hands are on the center of the bars. In this position the elbows are tucked in and the chin is on the hands. Also, the cranks are at 90 degrees and the knees are squeezed into the top tube. 

Advances in the aerodynamics of bicycle frames have also taken place starting in the 1980s. Among the first was to utilize oval tubing believed to help streamline the frame to reduce separation downstream of the tubes. Another trick is to add fairings to the seat tube. This fills in the gap between the tube and the wheel which, in turn, decreases the pressure drag. 

New handlebars have allowed riders to achieve an optimal aerodynamic position while still allowing for efficient pedaling. These handlebars allow the rider to achieve the same effect as the hill descent position while still allowing the rider to pedal efficiently. 

Aside from modern materials such as carbon fibers, bicycle manufacturers are eliminating some of the tubing to decrease the drag. Usually, the crossbar is eliminated as well as the chainstays. Some designers have eliminated the seat tube which they claim reduces the amount of separation behind the rider. They agreed that when designing an aerodynamic bicycle, the combination of the rider and the bicycle must be examined together. Bicycles are custom-fitted for the rider’s body.

As early as the late 1890s, one cycling journalist wrote that the importance of wheels to the production of aerodynamic drag has been known. At that time, a company in England produced a solid disk and a four-spoked aerodynamic wheel. These wheels are capable of reducing the overall drag of a bicycle and rider by about 5 percent. However, these original aerodynamic wheels were significantly heavier than typical spoked wheels. 

By cleaning up the protruding parts such as the derailleur and brakes and using smooth curves as opposed to sharp corners, modest reductions in drag can be obtained. Another important source of drag comes from the brake and derailleur cables and in order to eliminate the associated drag, cables are routed through the bike frame and handlebars whenever possible. When cables must be exposed, they are placed either immediately in front of or behind the bicycle frame. When taken as a whole, again, the experts believe, the overall drag reduction for a complete bicycle will be larger by utilizing aerodynamic components.

Racing cyclists often wear the creaseless ‘skin suits’ in order to reduce direct friction contributory to drag. They also shave their arms and legs of unwanted hairs. 

A helmet can also help to decrease the aerodynamic drag that a bicyclist encounters. Researchers have found out that an aerodynamic bicycle helmet reduces the drag by approximately 2 percent over a rider with no helmet. The right helmet not only protects your head, but can also give you a competitive edge in a bicycle race.*