Wheel aerodynamics can be enhanced two ways. One, through the reduction of air drag, and two, production of forward lift (sail effect).

1. Air drag is reduced by the elimination of frontal area, and by streamlining the remaining shapes. Narrow tires, rims, and reducing the number of spokes will reduce frontal area. Flattened spokes and "V" shaped rims are examples of streamlining shapes.

2. A bicycle wheel can only produce lift if there is sufficient surface area with the appropriate shape. The graphic explains how the right shape produces a forward push on the rim in a 10 - 30 degree headwind.
The effort is subtle and may be offset by the issue of stability in a high wind condition. Rim depths of over 50mm are necessary to produce lift and will experience a lateral push in crosswinds, which the rider must control. The benefit of a deep front rim over a semi deep design will be a 10 - 15 second reduction in an hour long event, -if a loss of control exists this advantage can easily be nullified. Using extra deep rear rims (or discs) with semi deep front rims seems to be the most secure solution, since the lateral push on the rear wheel doesn't effect the steering, only the lean angle of the bicycle. However, if the rider can handle it, deep rims or discs on both wheels will be the fastest setup aerodynamically.