Fatigue It is the phenomena of decay of the physical and chemical characteristics of the tyre rubber and textiles due to repetition of the stress cycles. It is strongly influenced by temperature. It depends on the operating conditions: inflation pressure, load, speed, type of driving, of road, road surface, external temperature, etc.

TIt is a vibrational phenomena which occurs when driving the vehicle after a long stop. The cause is the result of a temporary flattening of the tyre which causes annoying vibrations when rotating, and which generally disappear after a few kilometres, because the tyre heating up along with the centrifugal force makes the local deformation recover elasticity. In this case it is a passing problem. The ease with which the tyres recover their round shape depends on the size of the deformation which depends on the inflation pressure and the time the vehicle has remained stationary. It is thus a good rule to increase the tyre pressure of SR and TR series tyres up to 3.2 bar and up to 3.5 bar for the other series, including reinforced ones if the vehicle is expected to be parked for a long time with low temperatures especially in the open.

Contact zone between tyre and ground. The total footprint area is the sum of the net footprint area and the gap area. By net footprint is meant the sum of the contact areas of the tread blocks, by gap area is meant the area of the grooves and sipes in the contact zone.

Periodical vertical, lateral and longitudinal force variations with frequency the same as that of tyre rotation due to structure rigidity dissymmetry, run-out and distribution of the mass along the equatorial area of the tyre. See also evenness.

Maximum external radius of the tyre. It defines the maximum overall dimension of the tyre with respect to the rotation axle (tyre fitted to rim and inflated).

Surface interaction phenomena of two bodies in the contact area which gives rise to a reciprocal sliding friction, known as friction force. This force peaks at the beginning of sliding (breakaway friction) and generally decreases as the sliding speed increases.