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Bridgestone Explains Assen Tire Issues

Monday, July 9, 2012
Valentino Rossi had a terrible day at Assen  ending in 13th place.
Valentino Rossi at Assen where he suffered from severe tire chunking and lost position in the battle for a top-five finish.
At the German GP Bridgestone revealed the findings of a detailed analysis of the badly chunked rear tires that struck Valentino Rossi and Ben Spies during the preceding Dutch TT at Assen. Rossi was forced to pit for a new rear tire while he was battling for a top five finish after he lost large chunks of rubber of his Bridgestone tire. And Texan Spies saw his hopes of claiming a first rostrum of the season ended after he lost large chunks off his rear tire while battling for third with Italian Andrea Dovizioso.

Bridgestone immediately sent the affected tires back to its Technical Centre in Kodaira, Japan, where they underwent intensive analysis to determine the cause of the irregularities. Bridgestone’s Manager of Motorsport Tire Development, Shinji Aoki, was closely involved in the analysis of the rear tires he explained what the contributing factors were at Assen that caused the problems in the rear tires, and what measures Bridgestone will take to prevent such occurrences in future.

He said: “There were three riders who had problems with the right shoulder of their rear tire at Assen during the race, namely chunking of a piece of the tire’s tread due to excessive heating of the rear tire. Fortunately, none of the riders that experienced this issue crashed and the inner pressure of their tires remained normal. At Assen there were some factors that contributed to this potential increase in rear tire temperature. Compared to last year, the ambient temperature was substantially higher, the capacity of the engines in MotoGP machines has increased from 800cc to 1000cc which brought with it an increase in torque and machine weight, while the layout of the circuit also changed which resulted in a marked improvement in lap times. All these factors, in addition to the high camber of the Assen circuit, contributed to an increase in the potential for higher rear tire temperatures and when combined with certain bike setups and riding styles, resulted in excessive heat build-up that caused tread chunking of some rider’s rear tires. Though we were aware that this year’s Dutch TT would run under different circumstances due to the aforementioned changes in MotoGP machinery and weather conditions, we could not anticipate that these changes when combined with certain other variables such as particular riding styles and machine setup would result in such irregular rear tire behavior.”

Ben Spies and Andrea Dovizioso battled for podium position for much of the Assen TT.
Ben Spies (11) lost chunks of tire during a battle for podium position with Andrea Dovizioso (4) at Assen.
Aoki said the thorough investigation of the tires had not uncovered a defect with the tire or a manufacturing fault and he added: “We performed detailed analysis of the affected MotoGP rear tires from Assen, as well as other rear tires from the same batch as the affected tires and compared our results with analysis of a control set of tires from another production batch. All these tires underwent extensive testing, including a simulation on a specialized test rig that uses a drum rotated at high speed to test the durability and operating behavior of each tire. This analysis definitively showed that there was no manufacturing fault with the tires supplied at Assen.”

And speaking about future measures to prevent a repeat of the Assen problems, Aoki said: “Bridgestone will re-analyze its data from each circuit, including Assen, and use the lessons we have learned from last week’s Dutch TT to carefully consider the safety requirements and tire severity ratings for each circuit and will then decide if any additional events on the calendar should also be supplied with special construction tires. The difference in construction between last year’s tires and the 2012 specification was not a contributing factor to the generation of extreme temperatures on the edge of the tire and this was confirmed during evaluation of both specification tires on the rolling drum test rig. The construction of the 2012 specification tires does enable quicker warm-up performance, but this revised construction was not a factor in the excessive tire heating that caused the problems experienced at Assen.”

Aoki said Bridgestone did not anticipating any issues during the German Grand Prix at Sachsenring, which puts extra stress on the left shoulder of the tire with the tight and twisty layout dominated by left-handers.

“At Sachsenring it is usual for tire temperatures to be higher than at other circuits, so for this event we traditionally have supplied special construction tires that are specifically developed to handle extreme heat levels. So although relatively high tire temperatures are expected this weekend during the German Grand Prix, the tires supplied for this event are more than able to cope with this increase.”

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