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Tyre Glossary

Air Pressure Force exerted by air within tyre, expressed in pounds per inch.


Anchored Beads Ply and flipper construction which locks beads in place in the tyre. Rubber-coated cord fabric is wrapped around high tensile strength steel wire, which has been insulated with rubber. The ends of the fabric, which are several inches in length, are then carried far up into the sidewall of the carcass and locked in by the plies when the tyre is vulcanised.


Aspect Ratio A numerical term which expresses the relationship between the standing height of the tyre and the cross section width. (Aspect Ratio of 70 means the tyre section stands approximately 70 percent as high as it is wide between the sidewall.)

Bead That part of the tyre that is shaped to fit the rim. Made of high tensile steel wires that are wrapped in woven fabric and rubber, and then held by the sidewall cords.


Bias Tyre This type of tyre has layers of one ply cord material placed on the tyre carcass diagonally from one tyre bead to the other at an angle of 30° - 40° to the tyre's centreline.


Bias Belted Tires Have a body similar to that of bias tyres, plus two or more belts under the tread to strengthen and stabilize the tread. The belts improve tread life by reducing tread movement during contact without the road.


Carrying Capacity Maximum rated tyre load for a given inflation pressure as established by the Tire and Rim Association.


Chafer Reinforcing fabric and rubber around the bead in the rim flange area to prevent chafing of the tyre by rim parts.


Cord The twisted fibre or filament of polyester, rayon, nylon or steel which gives the tyre carcass and belts strength.


Inner Liner The layer of rubber which is laminated to the inside of a tubeless tyre to insure the air retention quality of the tyre body.


Light Truck Construction This description refers to a tyre specifically designed for more off-road strength and traction, towing on-road and a higher load-carrying capacity. It is usually used for 4WDs or SUVs. This term is synonymous with Heavy Duty construction.


Load Carrying Capacity Maximum load for which the tyre is designed under standard conditions at a specific pressure.


Load Range A system of designations, which identifies the carrying capacity range of a tyre. These markings shown on the tyre indicate the ply rating established for the tyre. Passenger tyre designations are B (4-Ply rating), C (6-Ply Rating) and D (8-Ply rating). This system was established by the Rubber Manufacturers' Association and is used on all American-made tyres.


O.D. (Outside Diameter) Measurement of tyre from top to bottom when inflated and mounted on rim.


Ply Layer of rubber-coated parallel cords forming unit of tyre carcass.


Passenger Construction This description refers to a tyre designed for on-road performance and handling with minor off-road usage. This term is synonymous with P-metric construction and Light Duty construction.


Polyester Cord A synthetic fibre that excels in maintaining strength properties at high heat levels, and eliminates flat spotting.


Radial Ply A tyre with cords running radically from bead to bead (90 degrees to centreline of the tyre).


Radial Tires Body cords run across the tyre perpendicularly to the beads. Radial tyres have belt plies, which run circumferentially around the tyre under the tread to stabilize the tread and strengthen the tread area. By restricting tread movement during contact with the road, the belt plies improve tread life.


Rayon An artificial fibre made from cotton or wood pulp by chemical process.


Revolutions Per Mile (R.P.M.) The number of revolutions that the mounted tyre will make in one mile, at rated load and inflation.


Rolling Resistance The resistance of a tyre to free rolling.


Section Width Measurement of distance through cross sectional width of a tyre at widest part, exclusive of scuffing rib when inflated to normal pressure and not under load.


Shoulder Outer edges of tread.


Sidewall The side of a tyre, typically marked or coloured distinctively.


Sipe To cut across a tyre tread to produce biting traction edges.


Speed Rating A speed designation shown in the size marking of some tyres, such as H, N, Q, S, T, V or Z.


Stability Ability of tyres to maintain direction of vehicle on curve without causing excessive sway.


Tread Depth The distance in millimetres measured from the tread surface to the tyre case.


Tread Design The pattern of the tread area.


Tread Elements The parts of the tread design, which are separated from each other and made distinct by the sipes and rib or lug designs, moulded into the tyre.


Tread Life Length of service in kilometres before tread wears out.


Tread Wear Indicators Narrow bars of rubber moulded at a height of 1.6mm across the bottom of the tread grooves. When the tread wears down to these bars, the tyre should be replaced.


Underinflation Tyre having less than recommended air pressure for the load being carried.


Weather Checking Fine hairline cracks in surface of rubber, caused by oxidation and other atmospheric effects.


Wheel Diameter The diameter of the wheel in inches.


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