As the car travels thru the air, the air is forced to flow around it...over it...under it. The air molecules don't go away, they just move.

The sources I've read through the years have all taken the position that the effects of a front air dam are two fold:

First-it increases the frontal area, and that leads to increased drag.

Second- it reduces the amount of air that is able to pass under the car, and forces it to flow around the car (and over it) which reduces the drag of the car (less air under the car equals less drag). The surfaces around the car are more aero, and the surface of the underside of the car is "dirty" creating more drag.

The sum of the influences are: The drag reduction under the car is greater than the drag created by the increased frontal area. Ergo, the sum effect is less drag, and more speed.

A splitter increases the amount of air forced to flow over the car.

We tend to forget the extremely dirty underside of the vehicles, and the negative influence it has on performance.

Good racing.

Bill