Following major problems with the rear tyres of three riders during last Saturday's Dutch TT at Assen, Bridgestone sent the tyres back to its Technical Centre in Kodaira, Japan, for analysis.
Most affected had been Ducati's Valentino Rossi, who was forced to make a pit stop for a new rear tyre during the race, while Yamaha's Ben Spies lost a podium place to Andrea Dovizioso after also shedding chunks from his tyre.
Bridgestone's manager of Motorsport Tyre Development, Shinji Aoki, was closely involved in the investigation. Here he explains what caused the problems and what measures will be taken to prevent such occurrences in future...
Aoki-san, can you explain what were the causes of the problem that some riders experienced with their rear tyres at Assen?
“There were three riders who had problems with the right shoulder of their rear tyre at Assen during the race, namely chunking of a piece of the tyre's tread due to excessive heating of the rear tyre. Fortunately, none of the riders that experienced this issue crashed and the inner pressure of their tyres remained normal.
“At Assen there were some factors that contributed to this potential increase in rear tyre 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 tyre 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 tyres.
“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 tyre behaviour.”
Were the affected rear tyres defective or have a manufacturing fault?
“We performed detailed analysis of the affected MotoGP rear tyres from Assen, as well as other rear tyres from the same batch as the affected tyres and compared our results with analysis of a control set of tyres from another production batch.