There are many forces that cyclists must overcome while riding. They must contend with rolling resistance and the effects of gravity which slows them down on a hill climb. They must also provide enough power to keep the bike moving forward, an even tougher task in a headwind. But perhaps the greatest influence on cycling comes from drag, which is partially overcome by making a cyclist and his bike as aerodynamic as possible.
Drag
Air resistance or aerodynamic drag is the result of the force of an object that resists its motion through a gas, which is essentially the air you must move through to keep your bike traveling forward. The amount of drag applied to a bicycle increases with both speed and surface area. Therefore, the faster a cyclist travels or the greater the area of his bike, the greater the amount of drag he will have to overcome.
Aerodynamic Forces
There are two forces applied by aerodynamic drag. They are direct friction and air pressure drag. When a bike and its rider disrupts the air, it forces it to separate away from the surface of the object. This is direct friction. At the same time, low pressure behind the object creates drag, which works to pull the bike backward. Direct friction can be decreased by wearing a smooth skinsuit and by riding a bike that has thin, aerodynamic tubing.
Increasing Aerodynamics
Many bikes are designed with aerodynamic tubing. Road racers during time trials and triathletes use deep dish wheels and disc wheels to decrease drag and increase their bikes' aerodynamic form. Because the cyclist's body also increases drag, cyclists wear tight lycra shorts and jerseys and during time trials, many wear formfitting skinsuits and special helmets to decrease drag and shave valuable seconds off their time. By decreasing their drag, they are also decreasing the amount of energy required to move at higher speeds.
Other Considerations
If you want to increase the aerodynamics of your own bike, begin by lowering the stem angle so that you are sitting less upright and in a more flat-backed position. Avoid wearing bagging clothing or bulky jackets. Use aerobars or the drops to get down low in a headwind or when you want to go faster. When riding with a group, save energy by sitting in a paceline. This reduces the wind drag on each rider except for the one in the first position.
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