A pneumatic tire includes a tread portion provided with a pair of center main grooves and a pair of shoulder main grooves to define a center portion, a pair of middle portions, and a pair of shoulder portions. The method comprises the steps of: detecting a first fault driving the motor to a maximum operating range; detecting a second fault forcing the motor to operate towards a minimum operating range; and generating a fault signal if both faults are detected substantially simultaneously. The recesses attach to the stamping apparatus.