Originally Posted by AMGLover

The main function of the spoiler is to eliminate the green area at the back of the car (see attached pic) admittedly one of the biggest issues with the go fast crowd is not hp - we can make tons of that - but wind resistance. The wind resistance on the front of the car goes up exponentially with speed, in the back drag - a vacuum is created as the car moves through the air - increases as well. If you look at the wind tunnel picture above you will notice on the spoiler down pic the smoke is almost solid at the back of the car = max drag. With the spoiler up the boundary layer is disrupted and swirls of air flow up from the bottom and drag is reduced. The XF has very good weight distribution and it is raked (nose lower then butt) so the car has decent down force. The spoiler is too small and too low (out of airflow to create much down force)...

Now this is a spoiler.



- ej