Glossary of Terms

ALIGNMENT

Refers to the correct angle settings of suspension components – the 3 alignment settings are caster, camber and toe. This is done to maintain specifications engineered by the vehicle manufacturer for optimum performance.


ASPECT RATIO

A numerical term, which expresses the relationship between the standing height of the tyre and the cross section width. For example: - An Aspect Ratio of 50 means the tyre section stands approximately 50 percent as high as it is wide between the sidewall.


ANCHORED BEADS

Ply and flipper construction that locks beads in place in the tire. 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 tire is vulcanising.


ASYMMETRIC

When opposite sides of a tyre’s tread pattern are not identical.


BALANCE

Equal distribution of the weight of a tyre and wheel. If a tyre & wheel is not balanced it can lead to vibrations or uneven wear. For balancing, weights are attached to the wheel to compensate for uneven weight distribution.


BACKSPACING

Also called rear spacing, it is the distance from the mounting pad to the back edge of the rim. This is different than wheel offset.


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 then held by the plies.


BEAD SEALER

Forms an airtight seal between the tyre and rim, reducing bead leaks. Bead Sealer is a thick, high-solid content, black sealant. Brush on the beads of tubeless tyres during mounting.


BEAD SEAT

The edge of the rim that creates a seal between the tyre bead and the wheel.


BEAD WEDGE

A metal, hooked shaped object to provide permanent gap between bead and rim.


BELTED BIAS TYRES

These tyres have a body similar to that of bias tyres, with the addition of 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.


BIAS TYRE

A tyre that is constructed with plies laid out in alternating directions in angles about 30-40 degrees to the centre line of the tyre. The plies form a criss-cross pattern.


BOOST AIR - CHEETAH

Blasts air under the bead forcing the beads into seats.


BUFFING SOLUTION

A chemical cleaner for repairing tyres.


CAMBER

The angle between the centreline of the tyre and a vertical line as viewed from the front.


CAMBER THRUST

A cornering force generated by the tyre’s chamber.


CARBIDE CUTTER

For drilling or reaming tyre injuries to correct size.


CARRYING CAPACITY

Maximum rated tyre load for a given inflation pressure as established by the European Tyre and Rim Technical Organisation (E.T.R.T.O)


CASING

The tyre body, composed of plies which for the tyre’s structure and give it shape. Sometimes called the carcass.


CAST

Wheels that are made from liquid metal being poured into a mould. Low-pressure casting involves pouring into a mould, while counter pressure casting involves sucking the metal into the mould like a vacuum. The counter pressure technique reduces impurities making the wheel much stronger than a low-pressure cast rim.


CASTER

The angle between the vehicle’s steering axis and a vertical line, as viewed from the side.


CHAFER

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


COMPOUNDING

The combining of five basic ingredients: rubber, carbon black, plasticizers, curing materials, and ozone retardants to form the tread and other “rubber” components of a tyre.


CORD

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


CROWN

The centre section of the tyre’s tread.


CURB GUARD

Extra rubber running around the sidewall of a tyre. It is there to protect the side of the tyre and the wheel face from any damage that may come as a result of hitting a curb.


DOT

Stands for Department of Transportation. The 10 digit code appearing after the DOT designation gives information such as week and year the tyre was produced, as well as the manufacturer, plant, tyre line and size.


DEFLECTION

The difference between a tyre’s unloaded or free radius and the loaded radius.


DIRECTIONAL STABILITY

The tendency for a tyre to rolling its steered direction rather than follow road contours.


DSST

Dunlop Self-Supporting Technology. An advanced tyre design that permits limited driving after loss of inflation pressure. Requires a pressure monitoring system.


FOOTPRINT

The area of the loaded tyre's tread that is in contact with the road. This is also called the contact patch.


FORGED

Considered to be the best wheel manufacturing technique, forging allows for the compression of an aluminium billet (one solid piece of aluminium) into an aluminium wheel using over 13 million pounds of pressure combined with heat. This produces a wheel that is both stronger and lighter then your standard aluminium wheel.


GROOVES

Circumferential channels between the tread ribs of a tyre.


HIGH PERFORMANCE TYRE

In the tyre industry, those tyres with speed ratings of S or greater and aspect ratios of 70 or less. 2.


HOOP STRENGTH

The retention strength inherent in the belt construction of a tyre that resists centrifugal force and provides dimensional stability.


HUB CENTRIC

A wheel with a centerbore made to match up with a vehicle's hub diameter.


HYDROPLANNING

Loss of traction at high speeds caused by a wedge of water that lifts a tyre off the road surface.


HUB CENTRIC RINGS - HUBRINGS

Hard plastic or aluminium rings mounted on a vehicle`s hub before the wheel. They ensure the wheel is perfectly centred on the vehicle`s hub. Without hub rings, there is a possibility of getting a vibration even if the wheel & tyre assembly is perfectly balanced.


IMBALANCE

The condition that exists when a tyre's mass is not evenly distributed around the rolling axis and centreline, causing bounce (static imbalance) or shake (dynamic imbalance).


INFLATION PRESSURE

The pressure of the air inside a tyre, which applies a tensile stress to the tyre cords, permits them to carry the vehicle's load.


INNER LAYER

The thin layer of halo butyl rubber inside a tyre that contains the inflation air, sometimes called the inner-liner. All Dunlop passenger tyres are manufactured with an inner-liner.


LOAD CARRYING CAPACITIY

Maximum load for which the tyre is designed under standard conditions.


LOAD INDEX - LOAD RANGE - LOAD RATING

A number used to represent the maximum weight a tyre can support. The index number corresponds to the actual load carrying capacity. Truck tires use a different system incorporating letter codes to establish a Ply Rating.


LOW PROFILE

A term describing a tyre with a relative aspect ratio or series classification.


M and S

A sidewall marking indicating that the tyre is approved for Mud & Snow use. This approval is made by the RMA (Rubber Manufacturers Association).


METRIC TYRE SIZE SYSTEM

A tyre sizing system using the section width (mm), aspect ratio, speed category, tyre construction, and the rim diameter (inches). Example: 185/70SR13.


P-METRIC SYSTEM

A tyre sizing system using the section width (mm), aspect ratio, type of tyre construction, and rim diameter (inches). Example: P225/70R15.


MIXING TYRES

Fitting tyres of different sizes, ratings or constructions to a vehicle. Mixing should be avoided as it may cause unpredictable handling. Some performance vehicles, however, specify different size tyres on front and rear axles. See vehicle's Owner's Manual.


MOUNTING TYRES

The act of fitting tyres to wheel rims.


Overall Diameter

The diameter of an unloaded, inflated tyre measured from the crown on one side to the crown on the opposite side. The free radius equals one-half of the overall diameter. Sometimes called the outside diameter.


OFFSET

The offset of a wheel is the distance from the mounting surface of the wheel to the true centreline of the rim. A positive offset means the mounting surface of the wheel is positioned in front of the true centreline of the rim / tyre assembly. This in effect brings the tyre in to the fender well more. Conversely, a negative offset means the mounting surface of the wheel is behind the true centreline of the rim / tyre assembly. This will cause the tyre to stick out away from the vehicle


OVER INFLATION

When a tyre is inflated more than the recommended vehicle air pressure. This might be done for better performance but has negative consequences including: a less comfortable ride, damage to the tires and stress on the suspension.


OVERSTEER

The situation that occurs in cornering when the rear of a vehicle tends to skid before the front and rotate in the original direction of travel.


POLYESTER CORD

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


PLY - PLIES

Layers of cord fabric that give a tyre its strength. They are situated between the tyre tread and the inner liner, and they run from bead to bead. These cords are rubber coated.


PSI

The most common measurement unit for tyre pressure. It stands for pounds per square inch and it measures the force exerted by the air inside a tyre.


RADIAL TIRE

A tire built with casing plies that cross the crown at an angle of 90 degrees.


RAYON

A fibre made from cotton or wood pulp by chemical process.


REGROOVING

Is a procedure that serves for increasing the tyre performance.  The regrooving of tread pattern can be made only on tyres marked REGROOVABLE. Regrooving is carried out after the tread is worn to 2 - 3 mm of residual groove and when it is still possible to make out the original tread pattern.


REPAIR PLUGS

Used for repair punctures in tyres, also known as mushrooms.


RETREADING

Applying new tread to a used tyre casing.


REVOLUTIONS PER MILE - RPM

The measured number of revolutions made by a tyre travelling one mile.


RIBS

Parts of a tyre tread pattern created by grooves that run circumferentially around the tyre.


RIM

The portion of a wheel incorporating the well, seats and flange onto which a tyre is mounted.


RIMTITE

Mounting paste for creating a professional seal on corroded rims.


RIM DIAMETER

The diameter of the rim bead seats that support a tyre are normally indicated in whole numbers in inches for passenger cars.


RING PROTECTOR

A Ring to fit over wheel prior to removal or fitment of the tyre to ensure no damage to the alloy wheel


ROTATION

Moving a vehicle's tyres from left to right and from front to rear. This is done in a set pattern and should be done periodically. Its purpose is to prevent uneven tyre wear and to extend tread life.


RUNOUT

The measure of the out-of-roundness of the tyre causing a vibration that cannot be balanced.


SECTION

A slice of a tyre from one bead, through the tread, to the other bead.


SECTION HEIGHT

The vertical distance from the bead edge to centre of the crown in an unloaded tyre.


SECTION WIDTH

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


SERIES

A numerical representation of a tyre’s aspect ratio; for example, 50 series.


SHOULDER

The outer edge of the tyre tread where it meets the sidewall.


SIDEWALL

The side portion of a tyre between the tread and bead.


SLIP ANGLE

The angle between the direction in which a tyre is aimed or steered and the actual direction of tyre travel.


SIPES

Small slits in a tyre's tread that help push water away from the crown of the tyre for improved wet traction. They also provide biting edges for ice and snow traction.


SPEED RATING

A letter that identifies a tyre's high-speed durability. A tyre's capabilities are tested at preset speeds and the results of these tests determine the tyre's speed rating. Speed Ratings include: Q, S, T, U, H, V, Z, W, Y


STABILITY

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


STEEL BELT

A belt material used in radial tyres. It’s high stiffness provides good handling and low tread wear.


TYRE PLACARD

A label on a vehicle that identifies the vehicle's stock tyre size and its recommended tyre air pressure. This label is often found on the inside of the vehicle's door.


AIR PRESSURE

The measurement of the force exerted by the air inside a tyre. It can be measured in pounds per square inch (PSI) or kilopascals (kPa).


TOE

The difference between the distances between the front left & right tyre and the distance between the rear left & right tyre. Toe-In means that the front of the tyres are closer together than the rear. Toe-Out means that the rear of the tyres are closer together than the front.


TREAD

The region of a tyre designed to contact the ground. It is moulded of tough rubber for high traction and low wear.


TREAD BLOCKS

Individual sections of the tread separated by lateral grooves.


TREAD DEPTH

The distance in thirty-secondths of an inch measured from the tread surface to the bottom of the grooves in a tyre.


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 PATTERN

The arrangement of blocks, grooves, sipes and channels designed into the tread to enhance its grip. Also called the tread design.


TREAD LIFE - TREADWEAR

Length of service in miles before tread wears out.


TREAD SHAVING

Shaving some of the tread from a tire for optimal performance and durability in racing applications.


TREAD VOID

Areas in the tread, such as grooves and channels, that permits water to drain away from the footprint.


TREAD WEAR INDICATORS

Narrow bars of rubber moulded at a height of 2/32" across the bottom of the tread grooves. When the tread wears down to these bars, the tyre should be replaced.


TUBELESS

A tyre construction that uses a rubber inner-liner inside the casing to prevent air leakage and eliminate the need for an inner tube.


TOURING PERFORMANCE TYRE

A tyre providing the ride comfort of a passenger car tyre, yet possessing high performance tyre characteristics.


UNDER INFLATION

The condition that exists when there is not sufficient air pressure in a tyre to support a specific load. This causes the tyre to operate with excessive deflection, mechanical flexing and heat.


UNDERSTEER

The condition that exists during cornering when the front of a vehicle tends to skid before the rear.


VULCANISING SOLUTION

Chemical compound used to bond patch or plug to tyre. Also known as glue /cement.


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.


U.T.Q.G

The Uniform Tyre Quality Grading rating is a quality rating system developed by the American Department of Transportation. It is designed to tell consumers the relative performance of passenger tyres (but does not apply to winter tyres).


WHEEL WEIGHTS

Weights attached to a wheel to balance a tire & wheel. The weights can be on the inside or outside of the wheel and can be clipped, taped or self-adhered to the wheel.


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