It is the international term adopted to define radial structure tyres. See radial structure.

Particular tyre in which the carcass consists of one or more plies with the cords arranged in a radial manner. The radial structure is inherently symmetrical and there can even be an odd number of plies. The pure and simple radial carcass is rather unstable; to make it stable and prevent dependant movement of the tread in the contact area with the ground, a ring-like reinforcing structure generally called a belt is located on the carcass and under the tread.

Particular tyre in which the carcass consists of one or more plies with the cords arranged in a radial manner. The radial structure is inherently symmetrical and there can even be an odd number of plies. The pure and simple radial carcass is rather unstable; to make it stable and prevent dependant movement of the tread in the contact area with the ground, a ring-like reinforcing structure generally called a belt is positioned on the carcass and under the tread.

It is a type of rounded section bead core, formed of a central ring-shaped closed core, around which a reel of thread whose diameter is less than that of the core is wound helicoidally until the central wire is completely covered. Bead core of this type is also prepared without the central thread core.

It indicates that the tyre has been reinforced. Tyres with this indication are usually used for equipping transport vehicles derived from motor cars.

Reliability means the capacity of the tyre in terms of quality of maintaining its performance unchanged in time, with specific reference to driving safety.

Reciprocal contact pressure between tyre and ground. It varies from point to point of the contact area.

Tread pattern element which joins two pattern blocks or two beads. It is generally less deep than the grooves and thus looks like a hump on the base of the groove.

It is a type of suspension made with a rigid connection between the two wheels of the same axle and thus the movements of one wheel are rigidly transmitted to the other. The most common types are classical and De Dion suspension.

It is the rigid metal element which connects the wheel hub with the tyre but not permanently.

It is the part between the two rim balconies. It can be flat, fluted, double fluted, deep fluted, etc. The lateral parts of the base are called seats.

Part of the base of the rim on which the sole of the heel rests.
Both the bead seats are inclined in order to favour the angular forcing and to block the heel on the seat. There are rim bead seats with a particular profile for tubeless tyres (see hump for example).

It is the distance between the centreline of the rim and line of the rim on the wheel hub.

The profile of the balcony which is designated with the letters C, D, E, F, J, K, etc. according to the different curve radiuses and the height of the balcony which determine it. The rim section overall shows a basic profile or trend determined by the two balconies; this trend or profile indicates the type of rim and that is channel, flat, hump, etc.

It is the minimum distance included between the inside of the balconies and represents the tyre seating area.

The radius of a rigid wheel which covers the same distance covered by a tyre, performing an equal number of turns. It has an intermediate value between the free radius and the load radius and varies for a given tyre according to the type of road and load, the pressure and the speed.

It is the force, applied to the wheel hub in the opposite direction to the vehicle's direction of movement, which opposes the tyre rotation and which is due to a variety of causes like material hysteresis, movement of the tread blocks on the ground, the ventilating effect of the tyres, etc. It is expressed by the ratio between resistant force and load applied x 1000.

It is a specific term which indicates irregular tyre geometry (force variation).