Tire Glossary

The optimum direction (relative to the road) to which all wheels & tires are pointed to.
Rolling over a film of water, it is the phenomenon caused by a tire that is building up a water front (like a wave) slightly ahead the tire itself. When speeding, this waterfront makes the car "surfing" on a certain portion of the water front itself, with the effect of lifting the car slightly off the ground: this is what causes a rapid loss of contact with ground, a quite scary sensation, when felt on the steering wheel by the driver.
The bottom part a tire that holds it onto the wheel rim.
Bead wires
Metal cords holding a tire tightly to the wheel rim.
Carbon black
In the tread compound chemical mix, a reinforcing filler agent that when put into the rubber increases the wearing resistance of the latter.
The tire's load-bearing framework.
Contact area
The surface over which a tire stays in contact with the ground.
The portion of the tread in contact with the road.
Actions & reactions: not all energy applied to a tire becomes totally absorbed by the latter, there is always an energy loss, that transforms into "heat". When dealing with an elastic material like rubber.
Load index
The load index represents the maximum load in kilograms that can be supported by the tire: the indices & their relative values in kilograms are reported in the appropriate tables.
Rolling resistance
The capacity of a tire to contrast its natural "spinning" movement. The lower the rolling resistance, the more economic it is to roll the tire as less energy will be required to "roll the tire" with a resulting fuel saving & higher mileage.
Service description
In addition to the Tyre Size Designation a tire may be identified by a Service Description consisting of a load index (or two Load Indices in the case of single/dual fitments) & a speed symbol.
The area of a tire where the tread & sidewall meet.
That portion of a tire between the tread & the bead
A reinforcing filler used with the rubber compound to provide higher wearing resistance & low rolling resistance.
Speed category
Indicates tire speed capabilities above 240 km/h & are included within the tire size designation e.g. 215/50 ZR 15. Generally, Service Description is not shown on such tires. For actual speed capabilities & load capacities, consult the tire manufacturer concerned.
Speed symbol
Indicates the max speed at which the tire can carry a load corresponding to its load index (except for speeds above 210 km/h) under service conditions specified by the tire manufacturer.
Tyre Compound
A "mix" or combination of raw materials used in the manufacture of the rubber compound of the tire itself. By varying the percentage or the composition of the materials applied, manufacturers can produce different tires for various purposes & with different performances.
Tyre Structure
Implies the method used to manufacture the tire carcass. The two main methods are "Radial" (a tire with plies arranged in a way that cords in the body run at 90 degree angles to the center line of the tread) & "X-Ply".
The area where the tread & sidewall meet.
Tread Pattern
The tire design or "sculpture". It varies according to the tire pupose (i.e. rain/wet are more grooves & channels for optimum water dispersion, whilst dry/tarmac tires are less grooved as they function is to maximize the contact area with the ground).
A tire inflated without a separate inner tube.
The device used to let air in or out of a tire.
Wear indicator
A rubber nub placed inside a groove of the tire tread to indicate the legal minimum depth of the groove itself.


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