Trim

When Formula One teams enter different races each season, they adapt their cars to best suit the track conditions. One such way they maximise the car performance is by manipulating the rear wing shape. This is because each track has different downforce requirements, and so the optimal downforce-drag balance is different for each track.

Here is a rear wing for a high-downforce circuit, Monte Carlo (Monaco Grand Prix), and a low-downforce circuit, Monza (Italian Grand Prix):

Comparison between the Mercedes rear wing at Monaco (High downforce) and the Mercedes rear wing at Monza (Low Downforce): formula1

Justification

The reason for changing the spec of the rear wing is so that, when the downforce requirement is small, the drag caused by a large rear wing area will outweigh the extra unnecessary downforce. As such, by reducing the wing area, the amount of drag also decreases.

Drag Reduction System

This system (known as DRS) is a system that assists overtaking drivers in getting past the car in front.

Design

There is an actuator on the rear wing that opens when the driver pushes the DRS button on their steering wheel. This opens a section of the rear wing (top) which drastically reduces drag by decreasing the effective wing area of the car, by allowing air to exit the rear wing through the open slot (below):

How F1 DRS works - Aero of Formula One DRS explained

This explains why there is NO DRS in wet races, where the loss in downforce would cause cars to lose control and crash, endangering safety.

Slipstream

The DRS adds to the effects of slipstream, which enables the following car to overtake the leading car.

How slipstream works is that the leading car creates a low-pressure zone behind it, which would offer less drag to the following car. In other words, the leading car ‘punches a hole’ in the air that would allow the following car to drive through with less air resistance.

F1 Aerodynamics : Slipstream explained | Bhat on Wheels

This should not be confused with dirty air. Dirty air is the turbulent air that the leading car leaves in its wake which reduces the effective downforce the trailing car can effectively produce. However, this is only most prominent in the corners and its effects are minimal compared with slipstream down the straights.