If something has a bluff body, the air breaks away whenever a sharp change in direction occurs. Frictional drag is the largest source of wind resistance for streamlined bodies, and pressure drag is the largest source of wind resistance for bluff bodies. A streamlined body will usually have better aerodynamics than a bluff body. Some parts of the cyclist and bike act streamlined and others act as a bluff body. Scientists study the combination of the drag of the streamlined and bluff bodies to find ways to reduce the overall wind resistance and improve the aerodynamics of the bicycle and rider.
Many variables affect rider aerodynamics.
The rider's position, clothing, and drafting patterns affect his aerodynamics. The aerodynamics of the rider is much more influential than the aerodynamics of the bike and its equipment. The torso of the rider is most aerodynamic in the horizontal position where it is parallel to the ground. This is the most important part of body aerodynamics because the torso is the largest part of the body and blocks the most wind. When a rider's torso is horizontal to the ground, his knees may hit his chest while riding.