This path also graphs the relative velocity of this point as it rotates through one revolution. The point will actually be at rest the moment it contacts the asphalt of the track, but will quickly accelerate to 40 mph as it approaches a position at the top of the wheel. The aerodynamic behavior of a derby wheel is important because four wheels rotating at high angular and linear velocities disturb a lot of air. The amount of energy required to move anything through air increases in value by the third power of the velocity of the object. Cd is the coefficient of drag of the racer.
V is the velocity of the racer with respect to the air.
The amount of energy lost by the racer to rotate four wheels through the air depends upon a complex determination of the instantaneous relative velocities and drag coefficients of all parts of the wheels. Further complicating the issue, the rear wheels partially draft from the front wheels. This means that the front wheels will have slightly more drag than the rear wheels. Not much can be done to offset this large amount of energy loss, as all racers are limited by the current rules of wheel enclosures. Some of this energy loss can be reduced by designing and using your axle trees to create turbulence in front of or next to your wheels, or by reducing the drag between the wheel and the axle tree.