Formula 1 for dummies: the choice of tyres in Formula 1

There are a number of rules that drivers must comply with when using tyres. It is a matter of fair play, as much as it is of safety. Within the boundaries of these regulations, each team plans its own strategy to get the most out of the sets they are provided. But what are the actual criteria underpinning the choice of tyres in Formula 1 racing?

For each race weekend, Pirelli nominates three dry compounds based on a number of factors. Certainly, these include the expected temperatures, the setting and above all the condition of the asphalt surface, which have a significant influence on the performance of the tyres. But even more important are the layout and the specific characteristics of the circuit, measured through a series of parameters that Pirelli discloses before every Grand Prix.

• Asphalt abrasiveness: this indicates how abrasive the track asphalt surface is and therefore how much of an impact it has on tyre wear.

• Asphalt adhesion: this indicates how much grip you can expect from the track, based on both the characteristics of that particular type of asphalt and on external factors such as whether sand is present, or the frequency of use of the circuit (is it permanent? Is it in a city?)

• Traction: this indicates how demanding the layout of the circuit is in terms of traction phases, i.e. when the tyre has to push the vehicle forward, especially when exiting slower corners.

• Braking: this indicates how challenging the circuit is for braking, when the tyres have to work together with the brakes to make sure the vehicle slows down.

• Lateral forces: this indicates how demanding the circuit is in terms of lateral forces, which affect the car especially when cornering: here the task of the tyres is to keep the car on track, resisting the forces that push it towards the outside at high speed.

• Tyre stress: this indicates the extent of the loads and speeds the tyres are subjected to along the circuit.

• Downforce: this indicates the level of aerodynamic forces pushing the car down. Downforce varies depending on how the teams configure the wings and other aerodynamic devices.

• Asphalt evolution: this indicates how much the conditions of the track are subject to changes during the weekend due to the amount of tyre rubber that is deposited on the track. This aspect is directly related to the level of abrasiveness of the asphalt and which compounds have been nominated.

Given the three dry compounds nominated by Pirelli, each team outlines a strategy to make the most of them during the Grand Prix. As a general rule, the hardest compound in the nomination (the P Zero White hard, which can be selected by Pirelli between C1, C2 or C3) is the one opted for to race the most laps because it is subject to less deterioration and consequently offers greater durability. It will be the preferred compound if the circuit has a very abrasive asphalt, if the temperatures are particularly high and if there are numerous areas along the track where the forces to which the tyres are subjected are high. The P Zero Red soft (C3, C4 or C5) is used for the opposite needs: it reaches the desired temperature more quickly, guarantees more ground contact and better grip. For this reason it is the compound with which the lowest times are recorded and therefore it is usually used in the decisive stages of the qualifying rounds. The flip side of the coin is clearly durability: the softer the compound, the more its durability will be reduced. Finally, the P Zero Yellow medium (C2, C3 or C4) is the most versatile solution in the nomination, mid-way between hard and soft that can be chosen for the moments of the race in which a balance between durability and speed is required.

Every Friday after FP2, depending on the times achieved during the sessions, Pirelli is able to calculate the performance gaps existing between the three slick compounds in the nomination, in other words how many tenths of a second separate the soft from the medium and hard on a lap of the track. Knowing the gap between the compounds is essential to prepare for the race. Thanks to the data acquired, including precisely the tyre gaps, a few hours before the start, Pirelli discloses the possible strategies that its engineers consider most effective to tackle the Grand Prix.

We use the term strategies because each team plans in advance which tyres its drivers will use during the race and after how many laps, with a certain degree of approximation, they will be called to the pit for a pit stop. However, this does not mean that things could change during the race, for a number of reasons. First of all, although the free practice sessions and the qualifying rounds can be representative, the race conditions are unique: the drivers drive in a situation that differs greatly from previous sessions and this can have repercussions on tyre behaviour. What's more, each team is influenced in real time by the strategic decisions made by their direct opponents. Strategies are a complex issue: the tyre change must be performed cleverly, with foresight and a bit of luck, because it can play a decisive role in determining the result of the race.