Valentino Rossi is about 1.5 year with Ducati, but he still can get his best performance on track. An interview from Enrico Borghi (Solo Moto Magazine) with Valentino Rossi told that the main problem for Rossi isn't the changes of cylinder capacity. One of the problem is the tyres.
I rode many bikes of all classes and of different brands, but more or less have always driven the same way. My style has evolved itself, but has always been essentially the same. When I tried the Yamaha in 2004, I found a bike that was not so different from the Honda was just slow, or it was a little worse. We frame things better and some worse, but after all the bikes were not that different. Now, however, I can not ride this bike, which is very different.
The tires from Bridgestone have no grip at maximum lean angle, as if they had the tires I have used until the end of 2008. With the single tire rule the tires have changed: when you're so inclined, I say a little less. This is, in my opinion, the biggest technical difference in recent years. It is clear that the bikes were piloted in a different way, entering curve, stop the bike, lift and speed, the curves pointing instead to round
800 or 1000, nothing changes. And far from the electronic influences both. The big difference technique is that the tires when you're really lying, and that held you before you let the bike turn more naturally: at maximum lean you began to accelerate. Now, however, is much more important to try to straighten the bike in the center of the curve, and you do it with gas, to exploit to the maximum acceleration after opening butt before.