Air Pressure
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The pressure of air inside the tire expressed in
pounds per square inch (psi) or kilopascals (kPa).
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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.
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All-Season Tires
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Tires designed for use on dry or wet pavement which
also provide traction on snow and ice.
Aquaplaning
See
hydroplaning
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Aramid
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A synthetic fiber that is, per weight, stronger than
steel. Used in tire construction and provides excellent high tensile
strength to weight.
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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
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Describes a tire's tread pattern which has one side
different from the other.
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Balance
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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.
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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.
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Bead seat
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The inner ledge portion of the wheel rim where the
tire bead rests adjacent to the flange.
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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
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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
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A tire tread pattern made of raised rubber- compound
segments.
Blocks
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The individual, raised rubber-compound segments
making up the tread of a tire.
Buckling
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A condition when a tire is bulging or crumpling.
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Camber
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The angle between the centerline of the tire and a
vertical line as viewed from the front.
Camber thrust
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A cornering force generated by the tire's camber.
Carcass
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That portion of a tire that is the foundation for
the tread, belts, bead and sidewall. See
casing.
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The tire body, composed of plies which form the
tire's structure and give it shape. Sometimes called the
carcass.
Caster
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The angle between the vehicle's steering axis and a
vertical line, as viewed from the side.
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A finishing strip of calendered fabric used to
protect the tire's bead area from the rim.
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Cold Inflation Pressure
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The amount of pressure in a tire, measured before a
tire has built up heat from driving.
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Compound
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The general term referring to the chemical formula
for the tire's material.
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Compounding
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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.
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Cord
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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.
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Contact patch
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(See Footprint)
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Cornering force
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The lateral frictional force generated by a
cornering tire, acting in opposition to the centrifugal force.
Crown
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The center area of a tire's tread.
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Deflection
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The deference between a tire's unloaded or free
radius and the loaded radius.
Directional stability
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The tendency for a tire to roll in it's steered
direction rather than follow road contours.
Drive Wheel(s)
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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.
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The area of the tire's tread that is in actual
contact with the ground. (also: Contact Patch)
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Friction
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The resistance to slippage between the tires and the
road surface.
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Grooves
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Channels between the tread ribs of a tire, also
called Tread Grooves.
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H-Speed or H-Performance
Rated
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A speed category for tires with a maximum speed
capability of 130 MPH.
Harmonic marking
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Markings on wheels and tires that allow match
mounting to cancel tire and wheel runout, minimizing vibration.
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A process of preparing competition tires for
use through controlled heating and rolling pressure.
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High Performance Tire
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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.
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Highway Tires
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Also called Summer tires; designed for wet-
and dry-weather driving, but not for use on snow and ice.
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Hoop strength
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The retention strength inherent in the belt
construction of a tire that resists centrifugal force and provides
dimensional stability.
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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
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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).
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Inflation pressure
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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)
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The interior layer of a tubeless tire. The
innerliner prevents air from permeating through the tire.
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Kilopascal (kPa)
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The metric unit for air pressure. There are 6.9 kPa
to 1 psi.
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Light Truck Tires
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Tires designed for off-the-road and on/off-the-road
use on sport/utility, small commercial and recreational vehicles.
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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.
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Load Index
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An assigned number ranging from 0 to 279 that
corresponds to the load carrying capacity of a tire.
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Load Rating
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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.
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Low-Profile
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A term describing a tire with a low relative aspect
ratio or series classification.
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Maximum Inflation Pressure
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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
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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.
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Mixing tires
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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
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The act of installing tires on wheel rims.
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Overall diameter
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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.
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Overall Width
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The distance between the extreme outer sides of a
tire's two sidewalls, including lettering and designs.
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Over inflation
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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
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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
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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.
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Passenger Car Tire
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Automobile tires featuring aspect ratios of 70 or
greater, using a taller profile for increased ride comfort.
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Plies (singular Ply)
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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.
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Plus-Sizing
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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.
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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.
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PSI or Pounds per square
inch
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The imperial unit for air pressure.
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Radial
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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
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Parts of a tire tread pattern created by grooves
that run circumferentially around the tire.
Revolutions per mile
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The number of revolutions made by a tire traveling
one mile.
Rim
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The portion of a wheel incorporating the well, seats,
and flange onto which a tire is mounted.
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Rim diameter
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The diameter of the rim bead seats that support a
tire, normally indicated in whole numbers in inches for passenger
cars.
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Rim Width
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Distance between the two opposite inside edges of
the rim flanges.
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Rolling Resistance
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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.
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Rollover
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The condition that occurs during hard cornering when
a tire sidewall rubs the road surface.
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Rotation
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The systematic movement of tires from one vehicle
position to another to maximize tread life and minimize irregular
wear.
Runout
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The measure of the out of roundness of the tire
causing a vibration which cannot be balanced.
Rim width
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The distance between rim flanges.
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S-speed or S-performance
rated
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A speed category for tires with a maximum speed
capability of 112 miles per hour.
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A slice of a tire from one bead, through the tread
to the other bead.
Section height
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The vertical distance from the bead edge to center
of the crown in an inflated, unloaded tire.
Section width
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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
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A designation of a tire's
aspect ratio. A
tire with an aspect ratio of 60% is a 60 series tire.
Shoulder
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The edge of a tire's tread where it joins the
sidewall.
Shoulder Blocks
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Raised rubber-compound segments on the part of the
tire tread nearest the sidewall.
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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
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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.
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Size
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The combination of tire width, aspect ratio,
construction type and rim size used in differentiating tires.
Examples: 175/70R13 or, 195/60R15
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Skid
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To slip or slide on the road when tires lose their
rolling grip.
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Slip angle
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The angle between the direction in which a tire is
aimed or steered and the actual direction of tire travel.
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Snow Tire
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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.
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Speed rating
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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.
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Steel Belt
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A layer in the construction of radial tires under
the tread. Its high stiffness provides good handling and low
treadwear.
Steer Wheel(s)
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Those wheel(s) which are used to steer or direct the
course of a vehicle.
Stud Holes
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- 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
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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.
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Tire Information Placard
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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
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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
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A tire providing the ride comfort of a passenger car
tire, yet possessing high performance tire characteristics.
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Traction
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The friction between the tires and the road surface,
or the amount of grip provided.
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Trailer Wheel(s)
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The wheel(s) of a trailer unit that neither provide
power nor direct the course of a vehicle.
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Tread
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The region of a tire designed to contact the ground.
It is molded of tough rubber for high traction and low wear.
Tread Blocks
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Raised rubber-compound segments on the outside
visible part of a tire.
Tread pattern
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The arrangement of blocks, grooves, sipes, and
channels designed into the tread to enhance its grip. Also called
the tread design.
Tread void
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Areas in the tread, such as grooves and channels,
that permit water to drain away from the footprint.
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Tread Width
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The width of a tire's tread.
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Treadwear
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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).
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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.
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Tubeless
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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
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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
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The condition that exists during cornering when the
front of a vehicle tends to skid before the rear.
UTQG
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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
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A speed category for tires with a maximum speed
capability of 149 miles per hour.
Varied-Pitch Ratio
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Variations in angles and sizes of a tire's tread
blocks to reduce noise produced by the tire when in use.
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Wear Bars
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See Treadwear Indicator.
Wheel alignment
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See Alignment.
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Z-Speed or Z-Performance
Rated
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A speed category for tires with a maximum speed
capability of over 149 miles per hour.
