Method for checking tyres, comprising: providing a tyre checking system, said tyre checking system comprising: at least a checking unit (19, 23) for finished tyres to be checked; an automated structure configured to move optical tools in order to carry out checking operations on the finished tyres, said optical tools being divided into at least a first group and a second group, said automated structure having a first mounting portion for integral association of the optical tools of the first group and a second mounting portion for integral association with the optical tools of the second group; providing a calibration apparatus, comprising a first engagement portion and a second engagement portion; associating each one of said optical tools, in sequence, with said first engagement portion, said first engagement portion comprising a replica of said first mounting portion and a replica of said second mounting portion; associating a reference element with said second engagement portion; for each optical tool associated with said first engagement portion, carrying out the following operations: adjusting the mutual position of the optical tool and of said reference element; detecting, through the optical tool mounted to said first engagement portion, one or more images showing at least a part of said reference element; performing a calibration of the optical tool based on said detected images; after calibration of said optical tools has ended and before activation of said tyre checking system: mounting one tool of the first group on the first mounting portion, the remaining optical tools of the first group forming a respective first store; mounting one tool of the second group on the second mounting portion, the remaining optical tools of the second group forming a respective second store; after activation of said tyre checking system: detecting a failure or malfunction of the tool mounted on the first mounting portion, and replacing the latter with a tool of said first store; detecting a failure or malfunction of the tool mounted on the second mounting portion, and replacing the latter with a tool of said second store. providing a tyre checking system, said tyre checking system comprising: at least a checking unit (19, 23) for finished tyres to be checked; an automated structure configured to move optical tools in order to carry out checking operations on the finished tyres, said optical tools being divided into at least a first group and a second group, said automated structure having a first mounting portion for integral association of the optical tools of the first group and a second mounting portion for integral association with the optical tools of the second group; at least a checking unit (19, 23) for finished tyres to be checked; an automated structure configured to move optical tools in order to carry out checking operations on the finished tyres, said optical tools being divided into at least a first group and a second group, said automated structure having a first mounting portion for integral association of the optical tools of the first group and a second mounting portion for integral association with the optical tools of the second group; providing a calibration apparatus, comprising a first engagement portion and a second engagement portion; associating each one of said optical tools, in sequence, with said first engagement portion, said first engagement portion comprising a replica of said first mounting portion and a replica of said second mounting portion; associating a reference element with said second engagement portion; for each optical tool associated with said first engagement portion, carrying out the following operations: adjusting the mutual position of the optical tool and of said reference element; detecting, through the optical tool mounted to said first engagement portion, one or more images showing at least a part of said reference element; performing a calibration of the optical tool based on said detected images; adjusting the mutual position of the optical tool and of said reference element; detecting, through the optical tool mounted to said first engagement portion, one or more images showing at least a part of said reference element; performing a calibration of the optical tool based on said detected images; after calibration of said optical tools has ended and before activation of said tyre checking system: mounting one tool of the first group on the first mounting portion, the remaining optical tools of the first group forming a respective first store; mounting one tool of the second group on the second mounting portion, the remaining optical tools of the second group forming a respective second store; mounting one tool of the first group on the first mounting portion, the remaining optical tools of the first group forming a respective first store; mounting one tool of the second group on the second mounting portion, the remaining optical tools of the second group forming a respective second store; after activation of said tyre checking system: detecting a failure or malfunction of the tool mounted on the first mounting portion, and replacing the latter with a tool of said first store; detecting a failure or malfunction of the tool mounted on the second mounting portion, and replacing the latter with a tool of said second store. detecting a failure or malfunction of the tool mounted on the first mounting portion, and replacing the latter with a tool of said first store; detecting a failure or malfunction of the tool mounted on the second mounting portion, and replacing the latter with a tool of said second store.