I had Pirelli back tire but now I changed to new one, Michelin Pilot Sport which is not so wide. Now even in normal wheelies I almost fall to right or left side. But the worst are circles... those are impossble to do whit the new tire!!! When I had Pirelli, circles were no problem at all... Is there anything I can do??

your tire pressure is at max...try with a less tire pressure

yeah, try with smaller preassure and give it time so the tire beats in a bit..