Function of Front Spoilers

Speed builds up a lot of air pressure below a car.

Front spoilers divert air from the car's underside to the vehicle's sides - thus reducing that lift created bythe air cushion below the car.

Side spoilers make sense as they stop that air diverted by the front spoiler from leaking back into the underside.

By diverting the air from the aerodynamically sub-optimal underside, spoilers also reduce a car's aerodynamic drag.

More Details:
http://www.racingcars.me/videos/how_an_automobile_front_spoiler_works