By regulation, the tyres feature a minimum of four grooves in them, with the intention of slowing the cars down. A slick tyre, with no indentations, is best in dry conditions. Both front and rear tyres are typically 660 mm in diameter. They can be no wider than 355 mm and 380 mm at the front and rear respectively. Slick tyres are rumoured to be reintroduced as of 2009 but the FIA regulations (though they can be changed) still have Formula One using "grooved" tyres in 2008.
There are several factors affecting the performance of formula 1 cars' tyres that should be considered before designing it. These factors include the road conditions, temperature, humidity, contact area with the ground and a few others. In tyre design, there are three main considerations - the profile and size, the tread, and the compound.
Racing tires are highly specialized according to vehicle and race track conditions. Tyres are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Tyres have also been specially engineered for drifting. Racing tyres are often engineered to minimum weight targets, so tires for a 500mile race may run only 300miles before a tyre change.
In 2005, tyre changes were disallowed in Formula One, the compound was harder as the tyres had to last the full race distance (around 300km). Tyre changes were re-instated in 2006, following the dramatic and highly political 2005 United States Grand Prix. For the 2007 season Bridgestone is the sole tyre supplier and have introduced four compounds of tyre, two of which will be made available at each race. The harder tyre is more durable but gives lesser grip, and the softer tyre gives more grip but is less durable. Both compounds have to be used by teams in a race and the softer tyre has a painted white stripe in the second groove. Each team must use each specification during the race, unless wet or intermediate tyres are used during the race, in which case this rule no longer applies. In extremely wet weather, such as that seen in the 2007 European Grand Prix, the Formula One cars were unable to keep up to the Safety Car in deep standing water due to the risk of hydro planing.
Rubbers used in tyres are generally styrene-butadiene co-polymers, natural rubber, or polybutadiene. These can be blended in whatever ratio is desired. The styrene content can be varied to give a hard wearing rubber, or a high styrene cling rubber to maximise wet grip at the expense of heat build up. Everything is a compromise aimed at giving the best performance for a particular application. For example, when a new circuit is laid down the surface is very abrasive, and polybutadiene has a superb abrasion resistance to sliding on sharp surfaces. However, it is hopeless in the wet, since grip suffers appallingly. In car racing of course, grip is everything.
The second most important variable is the carbon black type that is used. As a general rule, the finer the carbon black, the higher the abrasion resistance, and the higher the heat build-up in the rubber compound in service. There is another variable, the "structure' of the carbon black, a measure of the agglomeration of