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Formula One circuits - layer by layer 21 Nov 2006

Nico Rosberg (GER) Williams F28 spins in to the gravel. Formula One Testing, Valencia, Spain, 31 January - 3 February 2006. World ©  Patching/Sutton. Heikki Kovalainen (FIN) Renault Third Driver and Fernando Alonso (ESP) Renault walk the circuit.
Formula One World Championship, Rd 14, Turkish Grand Prix, Preparations, Istanbul Park, Turkey, 24 August 2006 Michelin engineer takes a track temperature reading.
Formula One World Championship, Rd 5, European Grand Prix, Practice Day, Nurburgring, Germany, 5 May 2006 Michael Schumacher (GER) Ferrari 248 F1.
Formula One World Championship, Rd 11, French Grand Prix, Qualifying Day, Magny-Cours, France, 15 July 2006 Michelin tyre on a McLaren Mercedes MP4/21.
Formula One World Championship, Rd 7, Monaco Grand Prix, Race, Monte-Carlo, Monaco, 28 May 2006

Beneath the surface of the Formula One track

The character of a Formula One circuit is not defined by its corners and straights alone. The surface itself is also critical, as it influences the grip of the cars as well as the erosion of the tyres. This has an impact on the set-up and race strategy. When deciding a circuit’s composition, however, the planners consider not only the performance of the cars but also the safety of the drivers and spectators.

The surface of a race track is almost always a compromise. When selecting the materials and composition of the asphalt, the architects are also determining the level of grip on the track which, as a rule, needs to be appropriate for both Formula One and motorcycle races. A circuit with only a little grip would lead to extended braking distances for cars and consequently to more overtaking, which would make the races more exciting. For motorcycles, however, this would be disastrous - extreme angles during cornering would cause them to slip as if they were riding on soap.

A race track is composed of layers. The first is the bearing layer, above that is the binding layer and, on top of that, the wearing layer - exactly as for normal road construction. The bearing layer consists of a thick sheet of coarse, watertight asphalt. The binding layer is applied on top of this foundation and serves to smooth out the natural unevenness of the bearing layer and secure the wearing layer above. Depending on weather and maintenance, the service life of a race track surface is between five and 10 years.

When selecting the materials for the asphalt - a mixture of stones and bitumen. The German engineer Hermann Tilke, who designed the new circuits in Bahrain, Shanghai and Istanbul, usually selects the best stone from quarries in the local vicinity. He then has the stone examined for suitability, as well as for wear and grip, in a test laboratory. The so-called ‘Lord of the Rings’ is not always satisfied with the results: the stones for the Bahrain International Circuit’s track surface had to be imported to the desert state from Wales at great expense.

As much as the surfaces of race tracks and standard roads may be similar, the stresses acting on them could hardly be more different. On a normal road, the greatest load is caused by the sort of weight when, for instance, a 30-tonne juggernaut brakes. On race tracks, the effects are the exact opposite. The hot tyres of the race cars develop an adhesive quality similar to tough chewing gum and pull the stones upwards. A tremendous strain is also created by the high speeds, which cause intense pressure in front of the cars and a vacuum behind them. Tilke describes the effects: “For the asphalt, this is as if someone was pounding it with a hammer at the front and hoovering it at the back.”

In everyday traffic, the road surface also has a strong influence on the tyres’ grip. This applies to the adhesion in dry conditions, but even more so to wet roads, where the so-called ‘macro roughness’ determines how quickly a film of water builds up. “The important thing is that drivers are not taken by surprise by unexpected changes in the grip of the road surface which might be caused by ruts in the road, patched asphalt or old or damaged road sections,” says Dr Christoph Lauterwasser of the Allianz Center for Technology. “By the same token, dangerous spots can also be made safer by the targeted, localised application of high-grip asphalt layers. This is suitable ahead of pedestrian crossings, at crossroads or on motorway ramps, for example.”

In Formula One racing, the question of how aggressive the track surface is to the tyres depends not only on the speeds driven and the number of braking operations, but also on the microstructure of the materials used. Tyre wear is particularly high at Barcelona and Monza, and is comparatively low on the slow street circuit in Monaco. Particularly good levels of grip are provided at Malaysia, Barcelona, Hockenheim and Suzuka, while the tracks at Melbourne, Imola, Budapest and the Nurburgring generally provide the poorest grip.

Williams engineer Frank Dernie appreciates the varied conditions and levels of difficulty. “It would be terrible if all race tracks were the same,” he explained to team sponsor Allianz. “Formula One is the class. Good drivers and good cars have to be fast wherever they’re racing!”