Running with a temperature
17/06/2008
One thing we hear rather a lot of from a tyre perspective in motorsport is ‘getting the tyres up to temperature,’ and temperature, whether it be ambient, track, or tyre, is an important area of interest for Bridgestone on many levels.
“Temperature in general affects many aspects of motorsport and for Bridgestone and our tyres it is a very important area,” confirms Director of Bridgestone Motorsport Tyre Development, Hirohide Hamashima.
Over the course of the season, Bridgestone visits 18 different circuits on five continents, with the season’s first grand prix taking place in March, and its last in November. Understandably, the temperatures seen at these races do vary.
“We see quite a big range of ambient temperatures at the tracks we visit,” says Hamashima. “And even at one circuit we can see a big range over a race weekend, and over the course of a day.”
Track temperature influences ambient temperature. Solar radiation heats up the ground and the tyre. Then the air gets heated by the ground. Direct solar radiation has a significant effect on tyre temperature, but the main contributions come from the track and air temperature, through conduction.
“At the circuit during a Grand Prix we constantly monitor the track and ambient temperature and when cars return from their runs we take temperature readings from the tyre tread. This is an important part of our data collection over a race weekend,” explains Hamashima.
“The ambient and track temperatures allow us to see the conditions in which the tyres are working,” explains Hamashima. “The tread temperature shows how the tyres are working.” There are two main reasons why temperature is so important: temperature working window, and tyre pressure.
“Every tyre has a designed temperature operating range in which it works best. If a tyre is too cold, it does not grip the road, if a tyre is too hot, then it also loses grip, and factors like blistering come into play,” explains Hamashima.
When Formula One moved to being in a sole tyre supply situation, Bridgestone developed tyres to have a wider temperature operating window to allow a less extreme performance profile. This allows teams and drivers to be better able to exploit the tyres’ potential, and the close nature of racing seen last season, and this year, illustrates the benefit of this to the sport.
Temperature affects pressure as air density changes with temperature, so the hotter a tyre becomes, the bigger the pressure change.
“Tyre pressure is very important to tyre performance too, and this is an area that the teams play very close attention to as they try to gain the maximum benefit from our tyres,” confirms Hamashima. “Our tyre is designed to supply maximum grip within a certain pressure range. Also if pressure gets too high the tyre becomes too stiff and the car starts to bounce. So we want to minimize pressure change during a run.”
Monitoring the temperature of the tyre is also a very good method of discovering how well the tyre is being used. When a driver returns to the pits, pyrometers, which are needle probes which penetrate the surface of the rubber to get a temperature reading, are used to take the tread temperature.
“Of course, over the course of a lap the temperature of the tyre will vary. Nor is the temperature over the tyre a constant, but we can learn a lot from our temperature readings from when the cars return to the pits,” explains Hamashima.
The tread temperatures are taken with three readings across the tyre: towards the inside edge, the centre and then towards the outside edge. For the teams, these readings can assist with car set-up.
For example, if temperature is even across the tyre this can illustrate that camber settings are correct. If the tyre is hotter on the outside edge then there could be too much positive camber; if it is hotter on the inside edge then there could be too much negative camber.
“Getting the best performance from our tyres is crucial for the teams to achieve a race good result so we collect a lot of data in this area, and our engineers advise the teams,” explains Hamashima.
Formula One is unique in motorsport in the respect that currently tyre blankets are in use, although this is set to change in the future. Tyre blankets heat the tyres so that they are at, or near to, their temperature operating window when drivers leave the pits.
“The removal of tyre blankets in the future will bring Formula One in line with other types of motorsport,” says Hamashima. “Without tyre blankets drivers and teams have to be very careful in their tyre management as they will leave the pits on tyres which are outside their temperature operating window.”
This change will make getting the tyres up to temperature more important, and place this more in the hands of the drivers.
“A tyre warms up in its usage through the movement of the rubber molecules as the tyre is put under various loads, and also heat transference from the heat generated through the brakes,” explains Hamashima.
“Warm-up for a tyre designed for use without tyre blankets occurs quite quickly and once up to temperature the tyre performs just like one which was pre-heated by blankets.”