The wings generate also drag, not only downforce and in straights it is really annoying. Downforce is good when you need higher friction force between tyre and asphalt: braking when entering a corner, in corners to allow higher centrifugal force without sliding, exit of corner (no wheel-spin when accelerating). And of course at start. Do you remember those flexible front wings used by Ferrari in '97 (one or two races, after that they've banned them. Hmmm FIA plot against Ferrari
)? They were bending in straights so generating less drag, but come back to original shape when the speed was lower (downforce again). <BLOCKQUOTE><font size="1" face="Trebuchet MS, Verdana, Arial">quote:</font><HR>From what I understand the rear wing creates "dirty air" behind the cars. This affects the overall downforce generated by the rear wing of a closely following car, up to 50% less.<HR></BLOCKQUOTE> I think, the worst effect is on the front wing of the following car. The downforce generated by front wing helps front (steering) wheels press harder on the asphalt and the car becomes difficult to handle in turbulent air.
There are also some other side effects, like disturbing the air-stream that is cooling the brakes (at least at front wheels) and radiators ==> overheating.
Anyway, not only the wings generate this dirty air. The problem is that the car is very dependent on them (if it likes to run fast). The car itself, not to mention the wheels, produces turbulent air also.