A look at the role of heat in Formula One tyre performance
Formula One racing visits two of the hottest locations in the calendar for the second and third races of the season with the Malaysian and Bahrain Grands Prix. As tyre suppliers Bridgestone explain, the heat experienced at these tracks will be a talking point for many reasons.
Temperature is a very important factor for a racing tyre at many levels, from production through to use on the track, and whilst you frequently hear commentators talk of drivers trying to get heat into their tyres, too much heat is not necessarily a good thing.
It's all to do with the working range in which the tyres are designed to operate. Racing tyres are designed to have a certain window of temperature where they work at their best and if the temperature is outside this window - whether too hot or too cold - the tyre is not rewarding the driver with its maximum potential.
"We have four different compounds available this season," explains Bridgestone's head of track engineering operations, Kees van de Grint. They vary in hardness and therefore there is a variation in grip level, heat and wear resistance. Each compound works best within a specific temperature window. If it does not come into that window then you will have a much slower lap time as the tyre grip is lower than its optimum. Equally, if you exceed the window, then there's a more or less similar situation, as the grip will reduce with the added difficulty of a chance of blistering for example.''
Predicting the weather is not an exact science and in times of a competitive tyre supply environment the working range of the tyre can be very narrow, making matching the tyre's working range to the weather conditions all the more critical.
In 2007, however, all teams have the same Bridgestone Potenza tyres so the focus has moved to the teams' cars getting the optimum from the four compounds (a maximum of two at each race) they will use over the course of this season.
"At those circuits where we can expect high temperatures we will use our hard and medium compounds," explains van de Grint. "During the competition days it was up to the tyre engineer to fine tune the selection of the right tyre as there were many options and smaller windows. But now it is up to teams to maximise their use of the tyres. We have selected the hard and medium compounds for the Malaysian Grand Prix, and I believe that the tyres can cope with the expected conditions. The car set-up and how the drivers use the tyres is the primary factor for success.
"For instance, if you have a situation where the rear of the car slides too much you will create more heat in the rear tyres than you actually want, which will not be such a good environment for the tyre to work in."
Tyres derive their heat on a race track from many quarters. Even before they have turned a revolution they are often at, or near, their optimum operating temperature thanks to the use of tyre blankets.
Tyre blankets are similar to the electric blankets people use to keep their bed warm at night and help ensure that the tyres don't have to go through the process of being warmed up on circuit every time, which can be a high-wear process as drivers throw their cars about and brake violently to get the tyre into the operating zone.
It's not just blankets that teams use either. Blankets wrap around the outside of the tyres and can give an uneven heat through the tyre construction, so the use of wheel rim heaters can mitigate against this, giving a warm and toasty rim for the tyre to mate with.
Then there is the situation before the start of the race where tyres could cool and out on track on the formation lap drivers use a variety of means to try to ensure that heat remains in the tyres, with rapid weaving and heavy braking.
"To get the tyre up to heat and stay in the window drivers do anything they can to keep temperature," says van de Grint. "The right temperature means grip and that is what a driver wants. But there is another very important factor involved. The temperature affects the tyre pressure. A decrease in temperature means a decrease in pressure and the added safety issues here."
Ensuring the pressure is at the right level when the tyre is in its working window gives plenty for teams to do. Road cars are usually filled with the same air that we breathe, but this is unsuitable for deriving maximum performance from a race tyre as its density varies due to temperature.
Bridgestone supplies their fitted tyres to the teams with dried air, but the teams then can refill their tyres with other gases such as nitrogen as an alternative solution.
Whilst a Formula One car can maintain a race tyre in its working window when driven at or near its maximum potential, there is a very real potential curve ball in the course of a race if a safety car comes out.
Driving at the lower speeds required under full course yellows means tyres can lose their heat and this makes it difficult for the drivers to judge just exactly how much grip they have at their disposal on the restart, as heat is regained in a far from perfect manner.
Both Malaysia and Bahrain have weather conditions which tend to be very hot. Malaysia tends to be heat with a high level of humidity, whilst Bahrain has produced one of the hottest Grand Prix of all time in 2005.
The 2005 Bahrain Grand Prix saw temperatures of over 100 degrees Fahrenheit (38 Celsius), and many have this on an equal footing with the 1984 United States Grand Prix at Dallas and the 1955 Argentine Grand Prix as the hottest ever'.
"What I remember very much about that race was that it was very difficult to cope with the heat as a human being, let alone the heat experienced by the tyres," says van de Grint.
Whilst Bahrain was a challenge, in Dallas in 1984 it was the track itself which was at issue with the surface breaking up to the extent that certain drivers were adamant that they did not want to race. As it was, the race did occur and Keke Rosberg - who had invested in a special cooling race helmet - went on to win.
In the 1955 Argentine Grand Prix it was the drivers who really felt the brunt of the oppressive conditions, and only two completed the distance without handing over to a reserve driver during the course of the event - an option which not at the disposal of their Formula One counterparts today.
Malaysia and Bahrain this season may not be as hot as these events, but last weeks group test at Sepang wasn't far off.
"Testing went well from a durability point of view, although the hard tyre could do with a little bit more grip on a green track. I think it is the right choice as we should not exchange safety for performance," concluded van de Grint.