This number certifies that the tyre is approved as laid down by regulation no. 30 of the European Economic Commission: the letter E indicates European approval, the number 3 represents the code of the Country which has issued approval, 02 indicates conformity with amendment 02 of regulation 30 and 39504 represents the number of the certificate of approval.

They are elements of the suspension of a car which elastically connect the car to the body, they cooperate with the bearing elements to improve comfort. They are: cylindrical springs, leaf springs, torsion bars, (pads, bumpers, rubber bushes).

These are vehicle suspension devices which cooperate with the elastic organs introduced with the aim of dissipating the energy stored and thus of attenuating the wheel and body vibrations. The dissipating element currently used on all types of suspension is the hydraulic or gas shock absorber.

It is the ideal circumference along which the equatorial line cuts the tyre and divides the tread in two equal and symmetrical parts, except in asymmetrical tyres.

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

This term is used to indicate the problems connected to rolling irregularities of the tyre on the road. If the wheel-tyre unit were perfectly symmetric, without discontinuity and if it moved in a straight line on a flat road, it would only be subject to load and transmitted torque forces. Otherwise a system of variable forces is manifested: if these forces are linked to dissymmetry (evenness) of the wheel-tyre their variation is periodical with the same period (frequency) as that of rotation.

Area of a tyre between the top of the tread and the widest transversal part of the tyre (chord).