Ride height
Ride height is how far the car sits above the track, and lowering it generally increases aerodynamic performance until the floor begins to touch.
Running low is quick and running too low is not: contact with the track wears the plank beneath the floor, and excessive wear is a disqualification at scrutineering.
It also changes through a race as fuel burns off and the car rises. Setting it is a bet on where the car will spend most of its time rather than where it starts.