Shanghai plays host to the next round of the 2007 MotoGP world championship, the Chinese Grand Prix, a race in which Bridgestone-shod Kawasaki rider Olivier Jacque excelled two years ago. Jacque, making his Bridgestone debut in MotoGP that season,...
Shanghai plays host to the next round of the 2007 MotoGP world championship, the Chinese Grand Prix, a race in which Bridgestone-shod Kawasaki rider Olivier Jacque excelled two years ago. Jacque, making his Bridgestone debut in MotoGP that season, stormed to a sensational second place just 1.7s from race winner Valentino Rossi in the first ever Chinese GP event, which showcased the competitiveness of Bridgestone's wet weather grooved tyres.
New technical regulations have altered Bridgestone's approach to wet tyre development since that race, as Tohru Ubukata, Manager of Bridgestone's motorcycle race tyre development, explains: "The tyre regulations we have in place for the 2007 season stipulate that wet tyres must have a land-sea ratio of at least 20% and that the grooves must be at least three millimetres in depth. In the past, we had no tyre limitations during a GP weekend, so we were able to produce 'cut slicks' which are slick tyres with small hand-cut grooves for damp conditions. The 31 tyre restriction prevents us from doing this so extensively this year, so we have had to make a wider range of wet tyres to cover full wet conditions and damp-drying conditions, since the number of wet tyres is not restricted by the regulations."
The characteristics of wet tyres differ greatly to their slick counterparts, which mean that any occasions to test in rain conditions are welcomed by tyre manufacturers. "There is a big difference between the design, construction and general characteristic of a wet tyre compared to a slick," comments Ubukata. "Wet tyres are not placed under so much stress as dry tyres because there is a slippery, protective filter of water between the track and the tyre. This also lowers the operating temperature, so we make our wet tyres softer with a greater operating window than the slicks which must always perform within tight performance confines at higher temperatures."
In order to achieve optimum performance in the slippery wet conditions, the tyres contain patterned grooves whose purpose are expressly to act as a water removal mechanism to obtain as much grip as possible from the circuit. The tyre compounds, even for wet specifications, are also adjusted to cope with the severity of the different circuits.
Bridgestone also benefits from a cross-over of its Formula 1 tyre development through the use of 'Hydro-Simulation Technology' at its technical centre in Japan. "We developed the Hydro Simulation Technology in Formula 1 tyre development several years ago, but recently MotoGP has also benefited," says Ubukata. "Essentially, it is a computer-based simulation which helps us to study the effects of the tyre's contact patch on a wet track to understand how different tyre patterns work to remove the water. The pattern of the tyre is important since it is designed not only to clear water, but it also has a separate effect on the grip level provided and it affects how the compound works. The work done on Hydro Simulation enables us to make good progress before we get to the race track, making wet tests crucially more efficient and productive. There is no real correlation between wet and dry tyre testing data," he says. "Whenever track conditions are wet, the test programme and test focus automatically shifts in order to maximise the opportunity to gain data. Wet tests are unpredictable and always useful because it is a rare occurrence that we have the chance to run in full wet conditions."
Highlighting the infrequency of wet racing, China 2005 was one of the last completely wet MotoGP races and Bridgestone's wet tyres helped Olivier Jacque secure a strong second place for Kawasaki, the team's best result of the season. "That was a strong performance and a real breakthrough for Bridgestone's wet weather tyres, which helped us reach a competitive level," says Ubukata.
"Last year's Australian GP at Phillip Island also gave us encouraging results. The weather was mixed with a dry-wet-drying track during the GP and the first time we saw riders forced to change bikes for wet tyres mid-race. Chris Vermeulen got a second place podium finish for Suzuki. When the track was fully wet, our tyres performed very well, but we could clearly see that our tyres needed more performance in the damp-drying conditions, so we have since developed a range of tyres to cope with such conditions. We recently verified the performance of these tyres in the post Jerez GP test, which gave us encouraging results.
The recent wet running in the post-Jerez GP test also enabled Bridgestone to gather interesting data from the 800cc machines for the first time. "From the Jerez test in March, we were able to understand that there is not a great difference between wet tyre performance using 990cc machines and 800cc bikes. It was the first time that we were really able to carry out a proper comparison in these conditions and the results have been beneficial in further developing our latest generation of wet tyres," concludes Ubukata.