Downforce

It grows with the square of speed, so it matters most on fast roads and tracks. Wings, splitters, diffusers and the underbody shape all create it. More downforce usually also means more drag. Racing cars can generate a large share of their grip from downforce, while most road cars are designed mainly to reduce lift.

Shaped surfaces deflect air upwards or speed it up under the car, creating lower pressure below than above.

Balance between front and rear downforce changes how the car handles at speed. Aftermarket wings that are not engineered for the car can upset that balance.