A modern Formula One car is a technical masterpiece. But considering the development effort invested in aerodynamics, composite construction and engines it is easy to forget that tyres are still a race cars biggest single performance variable and the only point of contact between car and track.
Traditionally, an average car with good tyres could do well, but with bad tyres even the very best car did not stand a chance. Things arent quite as clear cut in the current era - since 2007 every team receives tyres from a single supplier - but tyres are still a huge performance differentiator with newer, fresher tyres usually offering a significant advantage over worn rubber. As a result teams and drivers will carefully manage tyre usage over a race weekend to ensure they have enough sets of fresh tyres left for the race.
Despite some genuine technical crossover, race tyres and road tyres are - at best - distant cousins. An ordinary car tyre is made with heavy steel-belted radial plies and designed for durability - typically a life of 16,000 kilometres or more (10,000 miles). The current Formula One tyres last for, on average, around 120 kilometres and - like everything else on an F1 car - are lightweight and strong in construction. They have an underlying nylon and polyester structure in a complicated weave pattern designed to withstand far larger forces than road car tyres. In Formula One racing that means anything up to a tonne of downforce, 4g lateral loadings and 5g longitudinal loadings.
The racing tyre is constructed from a blend of very soft, natural and synthetic rubber compounds which offer the best possible grip against the texture of the racetrack, but tend to wear very quickly in the process. If you look at a typical track you will see that, just off the racing line, a large amount of rubber debris gathers (known to the drivers as 'marbles' because of their slipperiness). All racing tyres work best at relatively high temperatures at which point the tyres become stickier, although different compounds often have very different optimum working temperature ranges.
The development of the racing tyre came of age with the appearance of 'slick' untreaded tyres in the late 1960s and early 1970s. Teams and tyre makers realised that by omitting a tread pattern on dry weather tyres, the surface area of rubber in contact with the road could be maximised. Formula One cars ran with slicks until the 1998 when grooved tyres were introduced to curb cornering speeds. The regulations specified that all tyres had to have four continuous longitudinal grooves at least 2.5 mm deep and spaced 50mm apart. These changes created several new challenges for the tyre manufacturers - most notably ensuring the grooves' integrity, which in turn limited the softness of rubber compounds that could be used.
The 2009 season brought the much-welcomed return to slick tyres, following the FIAs decision to use new aerodynamic regulations rather than rubber as a way of keeping cornering speeds under control.
The rubber compounds used at each race are determined by the tyre supplier (currently Pirelli) according to the known characteristics of the track. Two different compounds of dry tyre are available to each team at every Grand Prix weekend - one harder 'prime' tyre and one softer 'option' tyre. Every driver must make use of both specifications during the race. The actual softness of the tyre rubber is varied by changes in the proportions of ingredients added to the rubber, of which the three main ones are carbon, sulphur and oil. Generally speaking, the more oil in a tyre, the softer it will be. However, whilst softer tyres generally tend to be quicker than harder ones, theyre also less durable.
Current F1 tyre suppliers Pirelli have a range of four dry-weather compounds: super soft (red sidewall markings), soft (yellow markings), medium (white) and hard (orange).
Intermediate and wet-weather tyres have full tread patterns, necessary to expel standing water when racing in the wet. However, sometimes conditions are too wet for even the full wet tyres to cope with. One of the worst possible situations for a race driver remains 'aquaplaning' - the condition when there is so much moisture on the surface of the track that a film of water builds up between the tyre and the road, meaning that the car is effectively floating. This leads to vastly reduced levels of grip. The tread patterns of modern racing tyres are mathematically designed to scrub the maximum amount of water possible from the track surface to ensure the best possible contact between the rubber and the track. At full speed the Pirelli intermediate tyre can disperse up to 25 litres of water per second, while the full wet tyre can disperse 60 litres per second.
Formula One tyres are normally filled with a special, nitrogen-rich air mixture, designed to minimise variations in tyre pressure with temperature. The mixture also retains the pressure longer than normal air would.
For more on the rules and regulations governing tyre usage over the race weekend, click here.