Originally Posted by Fajita Dave
Pirelli wasn't forced to change tires; they just didn't have a choice unless you want to see exploding tires in every race.
Not entirely true. Teams were using the tires on the wrong side of the car, too much camber, too low tire pressure, running them for too long etc. All against the guidelines Pirelli had issued. Basically teams were using the tires in a way they were not designed to perform. Teams wanted to gamble and find the extra tenth here and there. This along with the sharpie of a kerb in Silverstone added up for too much.
After that the tires were changed, but Pirelli also took more control over tire pressures, camber angles and usage of the tires.