The Panamera creates negative lift by deploying an upside-down wing from its tail. But a wing also generates drag, which “drags” down fuel economy. Porsche’s solution: Generate only as much negative lift as is needed for a given speed.
The Panamera’s wing remains stowed just below the rear window until 56 mph. At that speed, the wing deploys on motorized struts, up and out of the low-pressure boundary layer close to the body and into the denser air a few inches above, where it can get a good bite. It starts at an attack angle of -3 degrees, or with the leading edge slightly higher (the wing is upside down, remember).
Source: Car and Driver