1. A method of determining at least one characteristic of a tire selected from: the three components of a resultant of forces which are exerted by the road on the contact area of a tire, the self-alignment torque generated by the tire, the camber, and the pressure, the method comprising the steps of obtaining at least two measurements of circumferential extension or contraction in at least one sidewall of the tire at two fixed points in space, which points are situated at different azimuths along the circumference, and calculating said characteristic from said at least two measurements.