This is something that will blow your mind. I saw a show on PBS I think it was Nova, that dealt with the handling of Indy cars and the wings that they use on the front and back. They must be adjustable to get just the right amount of balanced down pressure. Too much or too little on the front leads to serious steering problems, understeer and oversteer.

Here's the really cool part. (Is "cool" a scientific term. Ha!)

The Indy car, at track speed, over 200 MPH, has so much down force on the car from the wings, that if physically possible you could turn the track upside down and the car would stay on the track.

Thanks to all of the above responses I now understand the differences between a spoiler "spoiling" the airflow to eliminate lift and a wing creating down pressure.

Maybe this Nova program is available on DVD.