pushing the air(like ur handout the window) is not the most efficient way of creating down force. you could write a book on wing shape so i wount get into that, but to say that it isnt so much the push(or snowplow effect, if thats easier) its the low/high pressure areas created above and below that create the force wanted.yes wouldnt they create the effect of holding your hand out the window more drag?
And yes could you explain im slightly retarded
think of it this way, you do not suck the liquid out of a glass with a straw. the extierior pressure is higher than the inner part of your mouth, when unequal, the pressures will even out, thus the liquid in your mouth.
now think of the liquid as the car/bike, when the pressure under a car is low, with a higher exterior presure, the car will be brought down to the tarmac.
ok that may have been over simplified but i hope it enlightens you somehow.
Matt