Bicycle aerodynamics is the study and practice of making both the bicycle rider and the bicycle itself as aerodynamic as possible to cut down on wind resistance and drag during a ride. Aerodynamics is essentially the study of air movement, and bicycle aerodynamics focuses on making air move more smoothly past a rider while he or she is moving at high speeds. Drag created by air passing over the rider can slow the rider down, sometimes making the difference between a win and a loss in a race. Clothing, helmets, and the bicycles themselves are often designed with aerodynamics in mind.
Some of the parts of the bicycle can be designed in such a way that drag is reduced. This facet of bicycle aerodynamics is perhaps the most important and expensive practice, since the bicycle frame itself is often modified or designed in such a way that drag is reduced. Carbon fiber frames, for example, can be molded in such a way that the frame tubing helps steer air around the bike and the rider instead of the air colliding with broad surfaces and slowing the rider down. Wheels can also be modified or designed to reduce aerodynamic drag; the spokes of the wheels can be bladed, which means they are flat on either side. When the narrowest sides of the spokes head into the wind, drag is reduced, as the air can quickly move past the spokes instead of colliding into them.
Other factors that can affect bicycle aerodynamics include cycling clothing, accessories, and the rider himself or herself. Helmets are often designed with bicycle aerodynamics in mind, and some helmets are designed specifically for certain cycling events, such as the time trial, in which the rider needs to go as fast as possible for a shorter period of time. The helmet will be generally smooth, and it will feature a wing or beak that extends backward in line with the rider's spine to help air move more efficiently past the rider's head.
The cyclist himself will often sit in certain positions to cut down on drag. The rider can sit with the arms and shoulders tucked inward to prevent air from being caught in the arms or the broadest part of the chest. The rider may often hunch forward with the head lowered to allow air to hit the shoulders and roll off the back, rather than having the air strike the chest.