The asphalt is a mixture of stones and bitumen. Great importance is attached to the selection of the materials, especially during the construction of new tracks. “We went to various quarries nearby and picked out the best stones,” said racetrack architect Hermann Tilke, who designed and built the circuits in Bahrain, Malaysia and Shanghai. The stones are tested for suitability in the experimental laboratory, and their wear and grip are investigated. The ‘Lord of the Rings’ was not always satisfied with the results – so the stones for the Bahrain International Circuit had to be carted at great expense from Wales to the desert state.

The loads that are applied to the asphalt on a racetrack are completely different from those on a normal road, so the bitumen is reinforced with polymer material. On a normal road, the greatest load is caused by ‘heavy load’, or the weight, for instance, when a 30-ton truck brakes. On a racetrack, the opposite is true: the heated tyres of the cars develop an adhesive effect and pull the stones upwards. This is combined with the high speeds, which create excess pressure in front of the tyre and low pressure behind the tyre. Hermann Tilke describes the effects as follows: “For the asphalt, it’s as though you were hitting it with a hammer at the front and applying a vacuum cleaner at the rear.” No wonder that the service life of a racetrack surface fluctuates dramatically – it can last between five and ten years, depending on the weather and maintenance.

By selecting the materials and the composition of the asphalt, the architects also determine the grip conditions on the track. If Hermann Tilke had a free choice and if the track was only ever used for Formula 1, he would also choose little grip. “The drivers don’t really like that – they prefer to have lots of grip,” he says, “but it does lead to exciting races, because the braking distances are longer and so it’s easier to overtake.” Less grip means less adhesion and so lower cornering speeds – and that means greater safety. Little grip would be a disaster for a track where motor-cycle races will also be held – riding at an angle, the riders would slip like on soft soap. “In most cases,” says the architect, “we agree on a sensible compromise.” However, experience shows that precalculated grip conditions are only reached after about one year.

“The grip of the tyres in normal road traffic also depends to a large extent on the road surface,” explains Dr Christoph Lauterwasser from the Allianz Centre for Technology. “Apart from large fluctuations in the adhesion in bad weather conditions, grip on a dry surface plays an important role in road safety. The grip level should be more or less equal in all areas, because a sudden reduction of adhesion can lead to serious accidents, especially with motorcycles. A specific increase in the adhesion in sensitive areas can reduce the braking distances and so contribute to traffic safety.”

In Formula 1, the question of whether the track surface is aggressive on the tyres or if the rubber is hardly worn at all depends not only on the speeds driven and the number of braking man-oeuvres, but also on the microstructure of the materials used. Tyre wear is particularly high in Barcelona and Monza. The load on the tyres is comparatively low on the city track in Monaco. The drivers enjoy particularly good grip in Malaysia, Barcelona, Hockenheim and Suzuka, but the tracks in Melbourne, Imola, Budapest and at the Nürburgring provide only poor grip.

In the case of the Autodromo José Carlos Pace, the host track for the Brazilian Grand Prix, the grip level and the tyre wear are both relatively low. According to Hermann Tilke’s theory, that means we can look forward to an interesting race with lots of overtaking.