Bridgestone’s Hamashima discusses Iveco TT Assen
The Dutch TT marked the first MotoGP victory for Yamaha’s Ben Spies, who becomes the tenth rider to win a premier class Grand Prix on Bridgestone tyres. Conditions all weekend made running very difficult indeed: the track temperature was a significant 29 degrees Celsius cooler than last year during the race, rain interrupted running every day and left the circuit very greasy, and an oil spill from the Moto2 category on Thursday cancelled the afternoon’s running and although it was cleaned up, it didn’t help track conditions.
Hirohide Hamashima – Assistant to Director, Motorsport Tyre Development Division
There was a great deal of talk of tyres all weekend. Firstly, what can you clarify what happened on Friday?
“Friday morning was the first dry running the teams got after the rain on Thursday, so it was the first day that riders used our slick tyres. We selected the same slick tyre compounds this year as we used at Assen last season, because our data and rider feedback suggested there was no reason to change. Track conditions on Friday morning were so bad though. Not only was the temperature cold but the track was slippery from the rain and I believe that some oil still remained from the spill, and that contributed to the riders feeling that grip was so bad on Friday morning. Riders requested a solution to their difficulty in warming-up the left side of the rear slick tyres at midday on Friday. Initially their request was for us to cut the slicks on the left side, which we were prepared to do, but finally there was no consensus between the riders so we were unable to proceed with this measure.
“Then we made a proposal of our own to bring a new rear slick tyre specification from our base in Germany overnight in time for warm-up and the race. This new specification featured a softer left shoulder, using our extra soft compound, so would have directly assisted with warm-up performance in this area. The right shoulder meanwhile was still the same medium compound as used in the original specification, which was performing well, so performance in this area would have remained the same.
“We were loading the truck in Germany, after the FIM asked all the teams and riders for their opinions and told us that the proposal was well received, however later on Friday evening we were informed that there was no unanimous agreement between the teams so we were unable to change the tyre allocation. Some riders didn’t agree because they didn’t feel there was a safety issue with our original compound selection. In the conditions we saw in the race on Saturday, I think the revised slick tyre specification we proposed would have been beneficial for the first few laps in terms of warm-up performance, but of course the trade-off of this would have been reduced durability over race-distance.”
In the race a few riders, especially Crutchlow and Edwards, experienced high front tyre wear. Why was this?
“We have seen that most riders usually prefer the harder spec front slicks as they have improved stability and wear resistance, and can be pushed harder through a corner and resist graining. However, seeing as conditions for the race were so cold and slippery, almost all riders chose the softer option front to be safe. The trade-off of the improved low temperature grip provided by the softer option is that it is more susceptible to graining. Bike setup and riding style also play a significant role in tyre performance and extracting the maximum performance from the tyres. Certain rider, bike and tyre packages were more severe on our front tyres, and as soon as a situation leads to the front tyre starting to grain, the issue gets increasingly worse.
“Assen has been resurfaced and remodelled many times over the years and so as a result it has a mix of tarmac, some of which is smooth and some abrasive. On the abrasive sections, especially through the long and fast right-handers, the wear resistance of the front tyre was really tested. For most riders it was not a problem, but clearly Colin, Cal and Andrea had a problem with front graining and wear rate.”
Is there any more news about the vibration Dovizioso experienced during the race?
“Andrea’s rear tyre had no problems – we have examined it and there was nothing out of balance with either it or the wheel, and nothing to indicate that the rear tyre was the cause of the vibration. Rather, all the signs point to front tyre graining being the cause of the vibration that Andrea felt through the bike. Basically, as the rubber grained, the right side of the tyre became slightly uneven, or not perfectly smooth, and this is what caused the vibration.”
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