Tyres are more than just black and round. Much more. They
utilise an innovative mix of chemistry, physics and
Many people don't understand the terminology when they enter a
tyre dealer or a mechanical workshop - below is a list of industry
terms to help you.
The amount of air inside the tyre pressing outward on each square
inch of tyre, which is expressed in pounds per square inch (psi) or
kiloPascals (kPa), the metric designation for air pressure.
Airtight Synthetic Rubber
Formulated with virtually impermeable butyl rubber, this material
replaces the inner tube in modern, tubeless tyres. Check you air
pressure monthly, as some air loss occurs over time.
When all wheels on the vehicle are adjusted so that they are
pointed in the optimum direction relative to the road and each
All-season high-performance tyres
Tyres that deliver a measure of traction on snow and ice without
sacrificing dry performance driving capabilities.
Tyres that provide a good balance of traction in rain or snow with
good tread life and a comfortable, quiet ride.
Indicates the tyre's ability to provide a balance of traction in
wet, dry, and winter conditions.
An advanced silica-based winter rubber compound that helps provide
flexibility where the tread surface makes contact with the
An extremely dangerous situation where water builds up in front of
the tyres resulting in the tyres losing contact with the road
surface. At this point, the vehicle is skimming on the water
surface and is completely out of control. Also called
A synthetic fabric used in some tyres that is (pound-for-pound)
stronger than steel.
The relationship of a tyre's sidewall height to its section
The state in which a tyre and wheel spin with all their weight
distributed equally. To correct an imbalance, a trained mechanic
will add weights on the interior or exterior of the wheel.
The section of the tyre that sits on the wheel. Inside, there is a
round hoop of steel wires, wrapped or reinforced by body ply cords,
that clamps the tyre firmly against the wheel rim.
A key component of the tyre that is the contact point between the
tyre and the wheel, designed to withstand forces the wheel puts on
the tyre during mounting as well as the dynamic forces of driving
Responsible for transferring propulsion and braking torque from
the wheel rim to the road surface contact area.
Bead Tension Structure
Two sidewall plies wrapped around each bead wire in opposite
directions providing lateral stability but flex to absorb road
A rubber-coated layer of cords that is located between the body
plies and the tread. Cords are most commonly made from steel but
may also be made from fiberglass, rayon, nylon, polyester or other
A type of tyre with crossed layers of ply cord running diagonally
to the center line of the tread.
The diameter of an imaginary circle drawn through the center of
each lug nut hole and then measured from two holes that are
directly across from each other. The measurement is used in
selecting the proper wheel for replacement.
A technique practiced by drag racers and road testers to improve
their off-the-line acceleration; applying the brake and throttle at
the same time, increasing the engine rpm until release of the
A term used to describe a loss of traction when negotiating a
curve or when accelerating from a standing start. The tyres slide
against, instead of grip, the road surface.
Synthetic rubber used to create today's tyres. It is virtually
impenetrable to water and air.
A wheel's inward or outward tilt from vertical, measured in
degrees. The camber angle is adjusted to keep the outside tyres
flat on the ground during a turn.
Side or lateral force generated when a tyre rolls with camber,
which can add to or subtract from the side force a tyre
This is a reinforcing filler which, when incorporated into the
tyre rubber compound, gives it a high resistance to wear.
The supporting structure of the tyre consisting of plies anchored
to the bead on one side and running in a radius to the other side
and anchoring to the bead. Also called casing.
Made up of thin textile fiber cables bonded into the rubber. These
cables are largely responsible for determining the strength of the
At a given air pressure, how much weight each tyre is designed to
carry. For each tyre size, there is a load inflation table to
ensure the inflation pressure used is sufficient for the vehicle
The angle between a line drawn vertically through a wheel's
centerline and the axis around which the wheel is steered; improves
a car's directional stability and on-center feel.
An imaginary line down the center of the vehicle. Alignment
tracking is measured from this line.
The sideways acceleration, measured in g's, of an object in
curvilinear motion. As a car traverses a curve, centrifugal force
acts on it and tries to pull it outward. To counteract this, the
tyres develop an equal and opposite force acting against the road.
Also called lateral force.
Cold Inflation Pressure
The amount of air pressure in a tyre, measured in pounds per
square inch (psi) before a tyre has built up heat from
The area in which the tyre is in contact with the road
surface. Also called footprint.
The strands of fabric forming the plies or layers of the tyre.
Cords may be made from polyester, rayon, nylon, fiberglass or
The force on a turning vehicle's tyres - the tyre's ability to
grip and resist side force - that keeps the vehicle on the desired
Provide the rigid base for the tread which allows for good fuel
economy. The plies also provide centrifugal and lateral rigidity to
the tyre, and are designed to flex sufficiently for a comfortable
Weight of a production vehicle with fluid reservoirs (including
fuel tank) full and all normal equipment in place, but without
driver or passengers.
The tread and sidewall flexing where the tread comes into contact
with the road.
The ability of a vehicle to be driven safely and with confidence
in a straight line and at high speed without being affected by
pavement irregularities, crosswinds, aerodynamic lifting forces, or
other external influences.
Track is the width between the outside tread edges of tyres on the
same axle. Tracking, or more specifically "Dog Tracking", refers to
a condition in which the vehicle is out of alignment, and the rear
wheels do not follow in the path of the front wheels when the
vehicle is traveling in a straight line. Also called tracking.
A code molded into the sidewall of a tyre signifying that the tyre
complies with U.S. Department of Transportation motor vehicle
Drift refers to a vehicle deviating from a straight-line path when
no steering input is given. Also called pull.
Mounting of a tyre wheel assembly in such a way that the center of
rotation for the assembly is not aligned with the center of
rotation for the vehicle's hub.
Filament at Zero
Individual, spiral-wrapped nylon or aramid/nylon reinforcing
filaments can be precisely placed in specific portions or across
the entyre tread area atop the steel belts banded at zero degrees.
Not only does this help retain tyre shape, but it also enhances
ride quality and steering precision.
Fore-and-Aft Weight Transfer
Transfer of weight from the front axle to the rear axle (or vice
versa) caused by acceleration or braking. Acceleration causes
weight transfer from the front axle to the rear axle. Braking
causes weight transfer from the rear axle to the front axle.
A handling term describing a car with its front and rear tyres
sliding in a controlled manner. The driver uses both throttle and
steering to keep the vehicle on a prescribed path.
The radius of the tyre/wheel assembly that is not
deflected under load.
The space between two adjacent tread ribs; also called tread
Gross Axle Weight Rating (GAWR)
The maximum weight that can be distributed among the tyres on a
Gross Vehicle Weight (GVW)
The weight of the vehicle and its contents (fluids, passengers,
Gross Vehicle Weight Rating (GVWR)
The maximum weight allowed for the vehicle and its contents. This
value is established by the vehicle manufacturer and can be
identified on the vehicle door placard.
A normal, safe occurrence in a tyre's sidewall where overlapping
splices of fabric cords form indentations. This cannot occur on
tread due to steel cable implantation.
The act of putting air into tyres.
The innermost layer of a tubeless tyre, compounded with virtually
impermeable butyl rubber. Some air loss over time will occur. Check
your pressures monthly to ensure safe reliable operation of your
The metric unit for air pressure. One psi is equal to 6.9
Lateral weight transfer
When a vehicle travels through a curve, weight is transferred from
the wheels on the inside of the curve to the wheels on the outside
of the curve. This is a result of the centrifugal force, or lateral
force acting on the vehicle.
Indicates how much weight a tyre is certified to carry at maximum
The measurement in inches from the wheel axle centerline to the
ground when the tyre is properly inflated for the load.
Loaded section height
The height of the section of the tyre that is making contact with
An assigned number ranging from 0 to 279 that corresponds to the
load-carrying capacity of a tyre.
Defines a range of maximum loads that tyres can carry at a defined
Wheels are manufactured to fit either the hub or the lugs.
Lug-centric is matching the lug holes of a custom wheel perfectly
to the lug pattern of the vehicle.
Luxury performance touring tyres
Generally designed for luxury sedans, this breed of tyres blends
performance handling with a comfortable, smooth ride.
Maximum inflation pressure
The maximum air pressure to which a cold tyre may be inflated; can
be found molded onto the sidewall.
Metric tyre size system
This is the act of putting a tyre on a wheel and ensuring that the
assembly is balanced. When you purchase new tyres, they need to be
professionally mounted. It is also standard for the tyre dealer to
charge a nominal fee for a valve stem.
The diameter of the inflated tyre, without any load.
The distance between the outside of the two sidewalls, including
lettering and designs.
Too much air in the tyre, resulting in premature wear in the
center of the tread.
The tendency for a vehicle, when negotiating a corner, to turn
more sharply than the driver intends. The rear end of the vehicle
wants to swing toward the outside of a turn. A handling condition
in which the slip angles of the rear tyres are greater than the
slip angles of the front tyres. An oversteering car is sometimes
said to be "loose," because its tail tends to swing wide.
Rust process that takes place in the steel belts when moisture,
via damage, is allowed to get inside the tyre. This can result in
the tyre becoming unserviceable before normal replacement
Abbreviation for pounds per square inch, which is the automotive
industry's measurement of the pressure in a tyre.
A condition in which a vehicle swerves to one side without being
steered in that direction, as a result of irregular tyre wear,
improper front and/or rear wheel alignment, or worn or improperly
That portion of a wheel to which a tyre is mounted.
The diameter of the rim bead seats supporting the tyre.
The linear distance traveled by a tyre in one revolution (its
circumference). This can vary with load and inflation. Rolling
circumference can be calculated as follows: 63,360 divided by
revolutions per mile = rolling circumference in inches.
The force required to keep a tyre moving at a uniform speed. The
lower the rolling resistance, the less energy needed to keep a tyre
The changing of tyres from front to rear or from side to side on a
vehicle according to a set pattern; provides even treadwear.
Rotating your tyres on a regular basis (every 6,000-8,000 miles) is
a simple way to add miles to their life. See your tyre warranty for
more information on recommended rotation.
A combination of raw materials blended according to carefully
developed procedures. The rubber compound is specially adapted to
the performance required of each type of tyre.
Run Flat Technology
Tyres that are designed to resist the effects of deflation when
punctured, and to enable the vehicle to continue to be driven at
reduced speeds and for limited distances.
The area of a tyre where the tread and sidewall meet.
Special slits within a tread block that open as the tyre rolls
into the contact patch then close, breaking the water tension on
the road surface and putting rubber in contact with the road to
maintain adhesion, increasing wet and snow traction.
The combination of tyre width, construction type, aspect ratio,
and rim size used in differentiating tyres.
The combination of steel cords covered with rubber that forms a
strip or belt placed under the tread rubber and on top of the
casing (carcass); ensures uniformity when the tyre is rotating and
helps prevent flats.
A vehicle's reaction to a driver's steering inputs. Also the
feedback that drivers get through the steering wheel as they make
The various springs, shock absorbers and linkages used to suspend
a vehicle's frame, body, engine, and drivetrain above its
Symmetrical Tread Design
Uniform tread pattern on both sides of the tread for better
performance in specific conditions and on specific roads.
Man-made, as opposed to natural, rubber. Most of today's passenger
car and light truck tyres have a relatively small amount of natural
rubber in their content.
Also called pneumatic tyre, a precisely engineered assembly of
rubber, chemicals, fabric, and metal, designed to provide traction,
cushion road shock and carry a load under varying conditions.
An alphanumeric code molded into the sidewall of the tyre that
describes the tyre's size, including width, aspect ratio, rim
diameter, load index, and speed rating. Most designations use the
A situation in which tyres of various brands, types, or sizes are
mixed on a vehicle. This can lead to variations in the vehicle's
ride and handling characteristics.
A metal or paper tag permanently affixed to a vehicle, which
indicates the appropriate tyre size and inflation pressures for the
vehicle. The placard can ordinarily be found on either the driver's
doorpost, the glove box lid, or the fuel-filler door.
Tyre Pressure Gauge
Tool used to properly measure the air pressure in a tyre.
The difference in distance between the front and rear of a pair of
tyres mounted on the same axle.
The fronts of two tyres on the same axle are closer than the rears
of the tyres.
The fronts of two tyres on the same axle are further apart than
the rears of the tyres.
Also known as Ackerman Angle. A vehicle's wheels on the inside of
a turn follow a smaller radius than the tyres on the outside of the
turn, because the two front wheels steer at different angles when
Turning or twisting effort, usually measured in lb-ft or Newton
A long, straight bar fastened to the frame at one end and to a
suspension part at the other; acts like an uncoiled spring that
absorbs energy by twisting.
The friction between the tyres and the road surface; the amount of
That portion of a tyre that comes into contact with the road. It
is distinguished by the design of its ribs and grooves. Provides
traction in a variety of conditions, withstands high forces, and
resists wear, abrasion, and heat.
The depth of usable tread rubber measured in 32nds of an inch. If
a tyre comes new with 10/32nds of rubber, you have 8/32nds of
usable rubber. Tyres must be replaced when the wear bars are
visible at 2/32nds.
The life of a tyre before it is pulled from service; mileage.
Operating a tyre without sufficient air pressure to support the
weight of the vehicle with occupants and additional load; could
cause failure of the tyre when heat is generated inside the tyre to
the point of degeneration of components.
The handling characteristic in which the front tyres break loose
because they are running a larger slip angle than the rear tyres.
Also known as plowing.
Material between the bottom of the tread rubber and the top layer
of steel belts; acts as a cushion that enhances comfort.
A device that lets air in or out of a tyre. It is fitted with a
valve cap to keep out dirt and moisture, plus a valve core to
prevent air from escaping.
Variable Contact Patch
A system that maximizes the contact patch area during cornering
through a combination of asymmetrical tread patterns and underlying
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The longitudinal distance from the center of the front wheel to
the center of the rear wheel on the same side of the vehicle.