Another interesting phenomenon associated with cars and cyclists is the phenomenon of drafting or "tailgating." It is well-known that the air resistance of a car following another in close proximity is reduced, and the leading car acts as a shield for the trailing car. The resulting flowfield is sketched in figure 12.1. The data shown in figure 12.2 indicate a significant decrease in drag coefficient for the trailing car when the separation is less than about one car length. Interestingly, the drag coefficient of the leading car is decreased by an even greater margin, suggesting that under race conditions both cars will travel faster in tandem than they could by themselves.

Figure 12.1 Schematic description of the aerodynamic interaction during drafting. From Race Car Aerodynamics, J. Katz, Robert Bentley Publishers, 1995.

Figure 12.2 Lift and drag variation for the two cars during drafting. From Race Car Aerodynamics, J. Katz, Robert Bentley Publishers, 1995. Originally from SAE Paper 710213.