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.
Traditionally, an average car with good tyres could do well, even very well, but with bad tyres even the very best car did not stand a chance. The move to a single tyre supplier in 2007 altered that equation somewhat, but, even now, optimizing the car-tyre balance is something of a black art.
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). A Formula One tyre is designed to last for, at most, 200 kilometres and - like everything else on a the car - is constructed to be as light and strong as possible. That means 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 very soft rubber compounds which offer the best possible grip against the texture of the racetrack, but 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'). All racing tyres work best at relatively high temperatures. For example, the dry 'grooved' tyres used up until very recently were typically designed to function at between 90 degrees Celsius and 110 degrees Celsius.
The development of the racing tyre came of age with the appearance of 'slick' tyres in the 1960s. 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 rule changes came into effect, and new tyre standards were introduced in an attempt to improve the spectacle of Formula One racing by reducing cornering speeds.
This led to the familiar sight of 'grooved' tyres, the regulations specifying 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.
Coming up to date, the 2009 season brings a much-welcomed return to slick tyres, following the FIAs decision to limit aerodynamics rather than rubber as a way of keeping cornering speeds under control.
The 'softness' or 'hardness' of rubber compounds is varied for each race according to the known characteristics of the track. Two different compounds are available to each team at every Grand Prix weekend, and 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.
Wet-weather and extreme wet-weather tyres have full tread patterns, necessary to expel standing water when racing in the wet. One of the worst possible situations for a race driver remains 'aquaplaning' - the condition when 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.
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.