The steering wheel of a Formula 1 car is a very complex component. It consists of various buttons, paddles, thumbwheels and dials. Any one of these or a combination can be used to control and/or adjust differential settings, engine modes and brake settings. A screen display allows the driver to monitor information and data.  The brake system of the car consists of composite carbon fibre brake discs. A hydraulic calliper squeezes both the front and the rear brakes with assistance from the energy recovery system of the power unit.  Pirelli is chosen as the sole supplier of tyres for Formula 1 cars. Pirelli offers five different compounds for dry tracks over a season. The team can choose any three compounds depending on the condition of the track, and during a race, two different compounds must be used for at least one lap between pit stops. An intermediate compound can be used on slightly wet tracks and a wet weather compound on tracks when it is pouring down.    The minimum weight of a Formula 1 car has to be 740 kg with the driver in the car but without fuel. Cars used to weigh much below before 2014. Cars are weighed with dry tyres fitted on the car. To achieve this weight cars use a ballast. The ballast can be placed anywhere to adjust the weight distribution of the car.