Term used improperly to indicate the chord measurement of a tyre.

It indicates the technical series of the tyre, 80,70,60 etc. It is symbolically indicated with the letter H.

It is the edge of the transversal section of the tyre fitted on the rim and inflated. It depends on the inflation pressure.

Maximum width of the tyre chord in millimetres and is indicated with the letter C.

It is the reason why the turned wheel tends to return to its normal position, parallel to the longitudinal axis of the vehicle. It is due to elastic reactions of the tyre carcass which occur in the contact area due to drift effect.

In addition to the Tyre Size Designation a tyre may be identified by a Service Description consisting of a load index (or two Load Indices in the case of single/dual fitments) and a speed symbol.

It is the element which dissipates the energy of the suspension, its job is to attenuate the vibration of the wheel and of the body. See energy dissipation devices.

It is the edge of the tread, between the corner of the tread itself and the beginning of the sidewall.

A layer of compound which protects the carcass, contributing to limiting the damage due to side blows or sliding as well as various incidents like cuts. It consists of natural rubber, synthetic rubber, carbon black, vulcanising agents and aging protection.

It is the area between the shoulder and the bead assembly. It is made up of a layer of rubber which protects the plies of the carcass from side blows for instance against the corners of the pavement.

A reinforcing filler used with the rubber compound to provide higher wearing resistance and low rolling resistance.

Term used to indicate a type of bead core made up of a single copper and rubber coated steel wire, wound several times to form the required section.

Thin grooves, generally in a jagged pattern or in any case divided finely which are located on the tread. The aim is to improve the traction, especially on smooth or wet road surfaces.

It is the indication on the sidewall of the tyre coded to distinguish the tyres according to some of their characteristic dimensions.

Terms used to indicate a type of tyre with a smooth tread or one with shallow circumferential grooves.

Synonym of slipping. It is better to use the latter term when referring to the vehicle and the former which referring to the movement of the individual areas of the tread compared to the ground.

It is an area of the behaviour which includes all the items which imply the use of tyres without losing transversal traction. The items are evaluated by going along appropriately chosen roads and motorways which contain a series of bends with large and small radiuses at different speeds. This part includes all the items which can easily be experienced by a driver under normal driving conditions (soft handling).

Regulation ECE/ONU 64, foresees that vehicles equipped with a smaller spare wheel may be authorised after providing proof that the wheel complies with the technical prescription contained in the regulation itself. Following this authorisation, the vehicle is authorised to circulate with a smaller spare wheel as long as it respects the speed limit of 80 km/h, observing the conditions of use established by the vehicle manufacturer and aware that it is a temporary situation which should be normalised as soon as possible.

Indicates tyre speed capabilities above 240 km/h and are included within the tyre size designation e.g. 215/50 ZR 15. Generally, Service Description is not shown on such tyres. For actual speed capabilities and load capacities, consult the tyre manufacturer concerned.

It corresponds to the maximum speed for using the tyre. The codes and the relevant values in kilograms are reported in special tables.

Maximum use speed index or code of the tyre reported in the special table.

Indicates the max speed at which the tyre can carry a load corresponding to its load index (except for speeds above 210 km/h) under service conditions specified by the tyre manufacturer.

It is the capacity of a tyre to re-establish the original balance position of a vehicle when internal (movement of the steering wheel) or external disturbing causes (variations of transversal road slope, side wind, etc.) have moved it. The effect that these forces exert on the tyre are given the name drift.

It describes tyres in which section height (H) and width (C) have a ratio which is equal to 0.8, which means that the section height of a given tyre is 80% its section width. H/C = 0.8.

It is caused by a weight placed symmetrically to the tyres centreline but not uniform along the circumference. With this imbalance the wheel vibrates in a vertical plane and the tyre undergoes a sequence of vibrations which increase in strength according to the speed of the vehicle and the weight of imbalance. The damaging effects of this phenomenon are a reduction in driving comfort, irregular tyre wear, early wear of some elements of the car (bearings, shock absorbers, etc.).

This is the angle formed between the wheel centre line and the longitudinal line of the vehicle: it is generated by turning the steering wheel.

Connecting element between the steering wheel and the steering elements. Mobile element on which the steering mechanism of the steering wheel operates allowing the appropriate rotation to be assigned to the leading wheels.

It is a series of mechanical elements which connect the leading wheels of the vehicle to the steering wheel and make it possible to steer.

Storage of the tyres to prevent their early ageing.

They are made of special steel and are applied to the tread of winter tyres for safer driving on ice. Some regulations laid down by the local highway code have to be respected; for instance in Italy the period of use goes from 15th November to 15th March, the maximum number of studs per tyre ranges from 80 to 160, the maximum projection is of 1.5mm, the speed limit is 120 km/h on motorways and 90 km/h on other roads, all the tyres of the vehicle and those of any trailers must have studs, splash guards must be fitted to the rear mudguards.

It is all the masses belonging to the vehicle which are laid on the suspension elements. It means everything above the elastic elements (body, transmission, passengers, etc.).

It is a series of mechanical elements which connect the wheels to the vehicle chassis or to the bearing body, making a significant contribution to passenger comfort, that is by absorbing the unevenness and the various irregularities of the road surface. From a functional point of view the elements of suspension can be divided into three groups: bearing elements, elastic elements and energy dissipation elements.

It is the damping of the vibration which is performed by the shock absorber.

It is the size of the vertical movement that the wheel can make compared to the body.