Tyre compounds

The three dry compounds are chosen per circuit from a wider range, so a "hard" at one race can be physically softer than a "medium" at another. That is a persistent source of confusion: the colours are relative to the weekend, not absolute. Softer rubber is quicker and wears out sooner, and the trade between the two is most of race strategy.

In a dry race a driver must use at least two different dry compounds, which is what forces a pit stop at all — without the rule, a team could run one set to the end and the racing would be poorer for it. The requirement lapses if the race is declared wet, which is why a rain-affected Grand Prix can be run without anyone making a scheduled stop.

Wet weather has its own two. Intermediates work on a damp track and a drying one; full wets clear far more water and are used when standing water makes anything else undriveable. Both wear quickly if the track dries under them, so a driver on the wrong one loses time in large chunks.

How long a set lasts depends on far more than the compound: track temperature, surface abrasiveness, fuel load and how hard the driver leans on it. Two cars on identical rubber can have entirely different afternoons.