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Air Pressure
The pressure of air inside the tire
expressed in pounds per square inch (psi) or
kilopascals (kPa).
The checking and adjustment of
caster, camber and toe angles in a vehicle's
suspension to maintain specifications engineered by
the vehicle manufacturer for optimum performance.
All-Season Tires
Tires designed for use on dry or wet
pavement which also provide traction on snow and
ice.
All Terrain
Tires with larger tread blocks designed to be used both on highways and off-highway driving
Aquaplaning
See hydroplaning
Aramid
A synthetic fiber that is, per
weight, stronger than steel. Used in tire
construction and provides excellent high tensile
strength to weight.
The relationship between the section
height and section width of a tire expressed as a
percentage of section width. If the section height is
one half the section width, the aspect ratio is 50%.
Low aspect ratio tires are also known as low profile
tires.
Asymmetric
Describes a tire's tread pattern
which has one side different from the other.
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Balance
The equal distribution of the mass of
the tire and wheel assembly for smooth driving.
Balance is achieved by fitting weights to the wheel
rim to offset uneven weight distribution of the tire
or wheel.
The part of a tire which is in
contact with the rim comprised of a round hoop of
steel wires, wrapped or reinforced by ply cords.
Bead seat
The inner ledge portion of the wheel
rim where the tire bead rests adjacent to the
flange.
The plies of tire cords beneath the
tread that determines the tire's diameter and
stabilizes the tread by resisting deformation from
cornering, braking, and centrifugal forces.
Bias-ply
A type of tire construction utilizing
plies that run diagonally from one bead to the other.
One ply is set on a bias in one direction, and
succeeding plies are set alternately in opposing
directions crossing each other. Sometimes called a
cross-ply tire.
Block Design
A tire tread pattern made of raised
rubber- compound segments.
Blocks
The individual, raised
rubber-compound segments making up the tread of a
tire.
Buckling
A condition when a tire is bulging or
crumpling.
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Camber
The angle between the centerline of
the tire and a vertical line as viewed from the
front.
Camber thrust
A cornering force generated by the
tire's camber.
Carcass
That portion of a tire that is the
foundation for the tread, belts, bead and sidewall.
See casing.
The tire body, composed of plies
which form the tire's structure and give it shape.
Sometimes called the carcass.
Caster
The angle between the vehicle's
steering axis and a vertical line, as viewed from the
side.
A finishing strip of calendered
fabric used to protect the tire's bead area from the
rim.
Cold Inflation Pressure
The amount of pressure in a tire,
measured before a tire has built up heat from
driving.
Compound
The general term referring to the
chemical formula for the tire's material.
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 tire.
Cord
The strands of material forming the
plies or layers of the tire. Cords may be made from
steel, fibreglass, rayon, nylon, polyester or other
materials.
Contact patch
(See Footprint)
Cornering force
The lateral frictional force
generated by a cornering tire, acting in opposition
to the centrifugal force.
Crown
The center area of a tire's
tread.
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Deflection
The difference between a tire's
unloaded or free radius and the loaded radius.
Directional stability
The tendency for a tire to roll in
it's steered direction rather than follow road
contours.
Drive Wheel(s)
The wheel(s) that provide the power
or driving force for a vehicle.
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The material used to fill the area
above the bead between the outer and inner portion of
the sidewall. Also used in enlarged form to stiffen
the lower sidewall of a tire.
The area of the tire's tread that is
in actual contact with the ground. (also: Contact
Patch)
Friction
The resistance to slippage between
the tires and the road surface.
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Grooves
Channels between the tread ribs of a
tire, also called Tread Grooves.
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H-Speed or H-Performance
Rated
A speed category for tires with a
maximum speed capability of 130 MPH.
Harmonic marking
Markings on wheels and tires that
allow match mounting to cancel tire and wheel runout,
minimizing vibration.
A process of preparing competition
tires for use through controlled heating and
rolling pressure.
High Performance Tire
1) Tires with speed ratings of S or greater and aspect ratios of 70
or less. 2) Yokohama uses the term for tires with an aspect ratio of 70
or less and a speed rating of H, V or Z.
Highway Tires
Also called Summer tires;
designed for wet- and dry-weather driving, but not
for use on snow and ice.
Hoop strength
The retention strength inherent in
the belt construction of a tire that resists
centrifugal force and provides dimensional
stability.
The accumulation of water in a film
under the footprint which causes a tire to lift from
the road surface, losing traction. Hydroplaning is
affected by vehicle speed, tread pattern, and water
depth. Also known as aquaplaning
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Imbalance
The condition that exists when a
tire's mass is not evenly distributed around the
rolling axis and centerline, causing bounce (static
imbalance) or shake (dynamic imbalance).
Inflation pressure
The pressure of air inside a tire
which applies a tensile stress to the tire cords
permitting them to carry the vehicle's load. Usually
expressed in Pounds per square Inch (psi)
The interior layer of a tubeless
tire. The innerliner prevents air from permeating
through the tire.
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Kilopascal (kPa)
The metric unit for air pressure.
There are 6.9 kPa to 1 psi.
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Light Truck Tires
Tires designed for off-the-road and
on/off-the-road use on sport/utility, small
commercial and recreational vehicles. Sometime called Sport Truck tires.
The thin layer of rubber inside a
radial tire that contains the inflation air,
sometimes called the inner-liner. Virtually all
modern passenger tires are manufactured with an
inner-liner.
Load Index
An assigned number ranging from 0 to
279 that corresponds to the load carrying capacity of
a tire.
Load Rating
A method of rating a tire's
load-carrying capacity (denoted by letters such as B,
C, D, etc.) with respect to its ply rating.
Low-Profile
A term describing a tire with a low
relative aspect ratio or series classification.
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M&S
Mud and Snow. Used to designate
a tire with special design characteristics to improve
performance in mud and snow.
Maximum Inflation Pressure
The maximum air pressure at which a
cold tire is designed to be operated, moulded onto
the sidewall. It should not be confused with the
vehicle manufacturer's recommended operating
pressure, which is frequently lower.
Metric Tire Size System
A tire sizing system using the
section width expressed in millimeters (mm), aspect
ratio, speed category, tire construction and the rim
diameter in inches. Example: 185/70SR13.
Mixing tires
Fitting tires of different sizes or
constructions to a vehicle. Mixing should be avoided.
Some performance vehicles, however, specify different
size tires on front and rear axles.
Mounting
The act of installing tires on wheel
rims.
Mud Terrain Tires
Tires with large tread blocks designed specifically for use in mud, sand, rocks and other off road driving conditions
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Overall diameter
The diameter of a mounted, unloaded,
inflated tire measured from the crown on one side to
the crown on the opposite side. The free radius
equals one-half the overall diameter. Sometimes
called the outside diameter.
Overall Width
The distance between the extreme
outer sides of a tire's two sidewalls, including
lettering and designs.
Over inflation
The condition that exists when a tire
is inflated beyond the pressure corresponding to the
actual load or beyond the vehicle manufacturer's
recommendation .
Oversteer
The situation that occurs in
cornering when the rear of a vehicle tends to skid
before the front.
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P-metric System
A tire sizing system using the
section width in millimeters (mm), aspect ratio, type
of tire construction and rim diameter in inches.
Example: P225/70R15.
Passenger Car Tire
Automobile tires featuring aspect
ratios of 70 or greater, using a taller profile for
increased ride comfort.
Performance tire
Tires which are designed to provide higher than average
traction at a speed rating of H or higher. The enhanced traction
may result in a shorter tread life due to the softer rubber compound
used.
Plies (singular Ply)
The reinforcing members of a tire
composed of layers of cord fabric and rubber that
provide the strength to contain the air pressure
needed to support a load and resist deflection.
Plus-Sizing
An option allowing drivers to
customize their vehicle by mounting low-profile tires
on wider rims of one or two inches greater diameter,
usually enhancing vehicle appearance, handling and
performance.
Ply Rating
The designation of a tire's strength
base on the equivalent number of cotton cord
plies. For example a tire with an 8 ply rating
may have only 2 plies, but have the same strength as
8 cotton plies.
PSI or Pounds per square inch
The imperial unit for air
pressure.
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Radial
The tire construction utilizing plies
that cross the crown at an angle of 90 degrees and
run radially from bead to bead under the tread. This
construction requires a belt to stabilize the tread
and define the tire diameter.
Ribs
Parts of a tire tread pattern created
by grooves that run circumferentially around the
tire.
Revolutions per mile
The number of revolutions made by a
tire traveling one mile.
Rim
The portion of a wheel incorporating
the well, seats, and flange onto which a tire is
mounted.
Rim diameter
The diameter of the rim bead seats
that support a tire, normally indicated in whole
numbers in inches for passenger cars.
Rim Width
Distance between the two opposite
inside edges of the rim flanges.
Rolling Resistance
The force required to keep a tire
moving at a uniform speed. The lower the rolling
resistance, the less energy needed to keep a tire
moving.
Rollover
The condition that occurs during hard
cornering when a tire sidewall rubs the road
surface.
Rotation
The systematic movement of tires from
one vehicle position to another to maximize tread
life and minimize irregular wear.
Runout
The measure of the out of roundness
of the tire causing a vibration which cannot be
balanced.
Rim width
The distance between rim flanges.
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S-speed or S-performance
rated
A speed category for tires with a
maximum speed capability of 112 miles per hour.
A slice of a tire from one bead,
through the tread to the other bead.
Section height
The vertical distance from the bead
edge to center of the crown in an inflated, unloaded
tire.
Section width
The distance between a tire's
sidewalls measured at the widest part of the tire,
not including lettering or designs. Each size of tire
is measured on a specific rim width.
Series
A designation of a tire's aspect ratio. A tire with
an aspect ratio of 60% is a 60 series tire.
Shoulder
The edge of a tire's tread where it
joins the sidewall.
Shoulder Blocks
Raised rubber-compound segments on
the part of the tire tread nearest the sidewall.
The portion of the tire between the
bead and the tread. This is the part of the tire
visible when in is installed on a vehicle and viewed
looking at the side of the vehicle.
Sipes
Slits in the tire tread which appear
to be small cuts in the surface of the tread that
improve traction and help in keeping the tire
cool.
Size
The combination of tire width, aspect
ratio, construction type and rim size used in
differentiating tires. Examples: 175/70R13 or,
195/60R15
Skid
To slip or slide on the road when
tires lose their rolling grip.
Slip angle
The angle between the direction in
which a tire is aimed or steered and the actual
direction of tire travel.
Snow Tire
Often referred to as a Winter
tire, a special type of tire with a tread and
compound that gives better traction in snow and other
extreme winter conditions.
Speed rating
A letter designation identifying the
tire's high speed durability on an indoor test wheel.
Refers to European Commission for Europe
Regulation 30 (ECE 30) European Indoor Wheel Test
Standards.
Sport Truck
See Light Truck
Steel Belt
A layer in the construction of radial
tires under the tread. Its high stiffness provides
good handling and low treadwear.
Steer Wheel(s)
Those wheel(s) which are used to
steer or direct the course of a vehicle.
Stud Holes
Small cavities along a tire's tread
designed to hold tire studs. See Studded Tire.
A special class of winter tire which
incorporated steel studs that protrude from the tread
for increased traction on snow and ice covered
surfaces.
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Tire
A precisely engineered assembly of
rubber, chemicals, fabric and metal designed to
provide traction and cushion road shock and to carry
a load under varying conditions.
Tire Information Placard
A metal or paper tag permanently
affixed to a vehicle that indicates the appropriate
tire size and inflation pressure for the vehicle, as
well as rim size and load capacity information.
Commonly located on the door edge or door frame of
the driver's side or on the inside of the glove
compartment door.
Toe
The difference between the front and
rear edges of tires mounted on an axle. Toe-in means
the front edges are closer together than the rear
edges and tires point inward. Toe-out means the front
edges are farther apart than the rear edges and the
tires point outward.
Touring Performance Tire
A tire providing the ride comfort of
a passenger car tire, yet possessing high performance
tire characteristics.
Traction
The friction between the tires and
the road surface, or the amount of grip provided.
Trailer Wheel(s)
The wheel(s) of a trailer unit that
neither provide power nor direct the course of a
vehicle.
Tread
The region of a tire designed to
contact the ground. It is molded of tough rubber for
high traction and low wear.
Tread Blocks
Raised rubber-compound segments on
the outside visible part of a tire.
Tread pattern
The arrangement of blocks, grooves,
sipes, and channels designed into the tread to
enhance its grip. Also called the tread
design.
Tread void
Areas in the tread, such as grooves
and channels, that permit water to drain away from
the footprint.
Tread Width
The width of a tire's tread.
Treadwear
A rating number moulded into the
sidewall of the tire ranging from 60 to 620
determined by tire manufacturers which compares tire
life against a predetermined standard tire (100).
Narrow bands, sometimes called
wear bars, located in the tire grooves which
are level with the tread surface when the tread
thickness is only 2/32 inch, or less.
Tubeless
A variety of tire construction which
uses a rubber inner liner inside the casing to
prevent air leakage and eliminate the need for an
inner-tube.
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Under inflation
The condition that exists when there
is not sufficient air pressure in a tire to support a
specific load. This causes the tire to operate with
excessive deflection and rollover.
Understeer
The condition that exists during
cornering when the front of a vehicle tends to skid
before the rear.
UTQG
Uniform Tire Quality Grade. A
US government Department of Transport requirement for
all tires sold in the USA. It is a tire rating system
based on a tire's performance in treadwear
durability, traction and temperature resistance. UTQG
ratings must be marked on a tire's sidewall.
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V-Speed or V-Performance
Rated
A speed category for tires with a
maximum speed capability of 149 miles per hour.
Varied-Pitch Ratio
Variations in angles and sizes of a
tire's tread blocks to reduce noise produced by the
tire when in use.
to Index
Wear Bars
See Treadwear
Indicator.
Wheel alignment
See Alignment.
Winter Tires
Tires specifically designed for use in winter driving
condition which may include rain, snow, and outside termperatures below
freezing.
Z-Speed or Z-Performance
Rated
A speed category for tires with a
maximum speed capability of over 149 miles per
hour.
