A Hot Choice

Two components are decisive in the successful fusion between car and tyre. Firstly, the rubber composition is crucial. The recipe is guarded like a state secret, and includes among other things, the following ingredients: rubber, filling material, carbon black, oils, resins, plasticisers and strength carriers. The manufacturers constantly experiment with hard and soft compounds. The rule of thumb is: the softer the tyre, the better the tyre grips, but soft tyres deteriorate faster, because the tread is rubbed away on the asphalt. Harder tyres last longer; but their reduced grip results in lower cornering speeds.

Secondly and ultimately, it all comes down to having the correct operating temperature. The trick lies in matching asphalt, air and rubber temperature. Each compound is specified for a precise temperature window. “This is why the specialists take temperature readings at the most varied points in the pit lane, in order to accurately record the asphalt temperature,” says Sam Michael, Chief Operations Engineer at WilliamsF1. This offers the tyre experts a reference point: due to the fact that the races around the globe all start at 2 p.m. local time, the asphalt temperature hardly drops below 10 degrees Celsius.

A difference of one to two degrees in circuit temperature is enough to change the temperature window in which a tyre performs to the best of its ability. According to Michael: “The tyre pressure is then matched to the asphalt temperature,” he says. The pressure in the front tyres is between 1.14 and 1.2 bar; the rear tyres are inflated to 1.02 to 1.08 bar. This can be summed up thus: if it is cool and the tyre too hard, then the car will slip just as much as if it was warm and the tyre too soft. As little as 0.1 bar more or less – or indeed even a difference in pressure between each tyre – is enough to ensure that a driver will not be able to chalk up any best times.

Before being deployed, the Formula 1 tyres that have been selected and inflated to the specified pressure, have to be quickly heated to the ideal operating temperature of roughly 100 degrees Celsius. Special coverings are used to heat up the tyres to 60 to 80 degrees. The tyres must start to perform after one lap. If they are too cold then they do not build up sufficient grip, if they are too hot they wear out faster. This can cause blistering which, under certain circumstances, could cause the tyre to blow-out. Generally, the useful life of a Formula 1 tyre is about 150 kilometres – dependent again on the compound, temperature and the driver’s driving style.

A time check demonstrates the significance of overall tyre performance. A few horsepower more, a new wing or some aerodynamic finesse may find that missing tenth of a second. The right tyre can make a Formula 1 car one second faster on a lap. That is a world of difference.

In other words, Formula 1 tyres are specialized items, with an extremely narrow temperature window to produce an ideal performance. By contrast, tyres designed for everyday road use, have a distinctly higher mileage. A normal road tyre should be good for 30,000 kilometres. In addition, it has a wider effective range. However, road tyres also have their limitations, so the change from summer to winter tyres should be made in good time. The decisive factor here is – as in Formula 1 – the operating temperature, which is dependent upon ambient temperature. As soon as the temperature falls below eight degrees Celsius, the rubber compounds of summer tyres provide noticeably less grip than in warm weather.

Dr. Hartmuth Wolff from the Allianz Centre for Technology in Munich recommends changing from winter to summer tyres and vice-versa in good time.
Vehicle expert, Wolff explains: “The softer winter compound and the more marked tyre tread not only serve to guarantee better grip and enhanced safety on ice and snow, but also on dry roads under eight degrees Celsius. This applies in particular when compared with high-speed summer tyres for speeds in excess of 210 km/h, which are designed for higher operating temperatures. Conversely, in spring, usually just after Easter, it is time to change the winter tyres over to summer ones. At constant temperatures in excess of 15 degrees Celsius, commercially-available winter tyres become too soft and the risk of tyre damage due to overheating at high motorway speeds is acute.” Thus, as on the circuit, so on the road: tyres which provide ideal performance and safety no matter what the weather simply do not exist. But they are working on it.