It is the angle measured in degrees between the vertical line and the line passing through the wheel centre line observing the car in front. The angle is conventionally considered positive when a tyre/wheel assembly is tilted outwards.

Reinforcement consisting of one or more layers of rubber coated fabric whose width approximately corresponds to that of the tread, located between the inner liner and the carcass plies in order to distribute the stress caused from blows on the ground and above all to improve the contact between tread and carcass.

Very fine, specially structured particles of carbon; used in rubber compounds as a reinforcing filler.

It is the resistant structure of the tyre and consists of one or more layers of rubber coated plies (rayon, nylon, polyester, steel, etc). Its job is to withstand the stress caused by the inflation pressure, by the load applied and by the force transmitted between the tyre and the ground during rolling (vertical, lateral, longitudinal). It contributes to driving comfort.

It is the angle measured in degrees formed by the steering pivot axis with the true vertical as viewed from the side. The incidence is considered positive if the projected extension of the steering pivot axis intersects the ground forwards of the tyre contact patch (referring to the direction of movement of the vehicle).

Common centre of the arches of concentric circumferences around which all the wheels of a vehicle must rotate on a bend to prevent the tyres from sliding.

It is an item of driving behaviour and expresses the measure of the stability of straight line movement; the best tyre does not require significant and frequent steering corrections to maintain the established straight trajectory.

It is the maximum transversal dimension of the inflated tyre, but not inflected (unloaded).

It is generally the comfort of both the driver and the passengers while the vehicle is in movement. This term is, however, difficult to define because it is strictly connected to individual physical and psychic sensitivity. It is obviously associated to vibration, mechanical (plastic comfort) and acoustic (acoustic comfort) phenomena which the tyres can also be affected by.

Tread design consisting of a series of elements with the same shape and longitudinal, arranged on the circumference.

Contact area between tyre and ground. The total contact area is given by the sum of the net contact area and the groove area. Net contact area means the sum of the tread blocks which touch the ground and groove area means that corresponding to the grooves included in the contact area.

It is the international term adopted to define conventional structure tyres.

Particular tyre structure in which the carcass ply cords are laid at alternate angles so that the cords making up a ply cross with those of the adjacent ply. The plies must always be laid in pairs for construction symmetry so that there is always an even number of them. This structure is, in any case, being abandoned for the radial structure.

A disturbing force that can act of on a vehicle when travelling in a straight line or cornering and which tends to modify its trajectory. The slip angle is that between the trajectory that the wheel would follow in the absence of a disturbing force and the actual trajectory followed.

Dimension corresponding to the coupling diameter between the tyre and the rim. Approximately equal to the distance between the diametrically opposite points of the bead base, it cannot, however, be directly measured on the tyre because of forcing or play between tyre and rim.

It is the distance between two diametrically opposite points on the circumference resulting from the ideal intersection of the bead seat with the rim balcony. This dimension strictly depends on the corresponding dimension in the tyre.

Two symmetrical elements fixed to the drive wheel drums and hinged to the coupling bar which connect them.

It is one of the elements of the tyre, consisting of a non extendible and non rigid shell which couples with the rim. It is the bearing structure of the tyre in contact with the road and thus capable of resisting the internal air pressure and all the other stress coming from use.