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all air at front of car has to get to back of car at same time, regardless of whether it goes (a) over, or (b) under car.
distance under car is shorter than distance over car.
hence, physics says air traveling over car has to travel faster than air under car in order to arrive at back at same time.
faster air has lower pressure.
car gets sucked up by pressure difference.
just like an airplane wing.
at slow speeds effect is negligible.
at high speeds you start to see impact.
ways to mitigate:
- front splitters and side rocker panels reduce amount of air under car.
- rear diffusers lengthen under car distance and reduce effect.
- spoilers (not wings) disturb airflow and move 'delamination' point (where smooth, 'laminar' flow over hood, windshield, and roof, separates from car and becomes 'turbulent' flow that no longer contributes to lifting effect) further forward.
all this to reduce lifting effect caused by 'wing' shape of car.
there is also downforce - this is different - this is where you get air to push the car down:
- front canards
- venting radiators upwards
- venting fender liners
- wings (reverse airfoils) on rear of car
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