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A
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Alignment
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Adjustment of all the wheels on the vehicle to make them point in
the same optimum direction relative to the road and each other.
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All-Season High-Performance Passenger Car Tire
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Generally designed for luxury four-door sedans, this line of tires
combines high-performance handling and a smooth, comfortable ride.
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All-Season High-Performance Tire
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Provides great traction in snow and on ice without sacrificing
performance on a dry road.
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All-Season Tire
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Provides a good balance between traction on a wet or snow-covered
road, tread life and a smooth, comfortable ride.
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Aquaplaning (or hydroplaning)
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Extremely dangerous situation where water accumulates in front of
the tires, making them lose contact with the road surface. The vehicle then
skims the surface of the water and loses control.
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B
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Bead
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Section of the tire resting on the wheel. Inside is a hoop of steel
wires, wrapped or reinforced by ply cords that firmly hold the tire unto the
wheel’s rim.
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Belt
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Layer of cords coated with rubber located between the plies and the
tread. These cords are typically made of steel but can also be made of
fibreglass, rayon, nylon, polyester or other fibres.
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C
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Carcass (or casing)
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Tire’s support structure made up of plies anchored in the bead of
one side and anchoring itself according to a radius in the other side’s bead.
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Cold Inflation Pressure
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Amount of air pressure in a tire, measured in pounds per square
inch (psi) before the tire has built up heat from running.
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Contact Surface
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Point of contact between the tire and the road surface. Also called
footprint.
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Cornering Handling
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The force exerted on tires during cornering—the ability of the
tires to stick to the ground and resist lateral force—maintains the vehicle in
the desired angle.
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D
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DOT Rating
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Code moulded on the sidewall of a tire indicating that the tire
complies with the U.S. Department of Transport safety standards for motor
vehicles.
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Dual Tires
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Tires mounted side by side on an axle for the purpose of increasing
the load and grip capacity; four tires on an axle.
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Dynamic Balance
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Exists when the weight is evenly spread both along the
circumference and on each side of its longitudinal axis. A tire-wheel assembly
out of its dynamic balance will produce fluttering of the wheels, or shimmy.
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E
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Extra Load
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Tires that can support higher loads because their maximum inflation
pressure is higher than the standard maximum.
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F
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Free Diameter
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Diameter of the unloaded, inflated tire.
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G
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Groove
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Space between two adjacent ribs.
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Gum Compound
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Combination of raw materials according to carefully established
processes. Such compound is adapted according to the performance required for
each type of tire.
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H
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Handling
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Normal control of a vehicle by the driver.
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High Floatation System for Light-Duty Trucks
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Tires with lower sidewalls and wider tread designs providing better
grip on surfaces like sand or off-road soft soil.
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High-Performance Tire (or maximum performance/ultra-high
performance)
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Tire whose handling, traction and cornering grip are superior to
standard tires. High-performance tires are also rated for running at higher
speeds than other tires.
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I
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Inflation Pressure
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Amount of air inside a tire exerting outward pressure on each
square inch of tire; expressed in pounds per square inch (psi) or in kilopascals
(kPa — metric designation for air pressure).
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K
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Kilopascal
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The metric unit for inflation pressure. One psi (pound per square
inch) equals 6.9 kPa.
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L
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Load Limit
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Defines the maximum load a tire can carry with a determined
inflation pressure.
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Load Rating
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Indicates the weight that the tire is certified being capable of
supporting under maximum tire pressure.
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Load Rating
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Number included between 0 and 279 corresponding to a tire’s load
capacity.
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M
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M+S, M/S or M&S
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All-season rating for tires offering a certain degree of
performance in mud and snow. Meets the standards of the Rubber Association of
Canada regarding mud and snow tires.
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Maximum Inflation Pressure
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Maximum air pressure to which a cold tire may be inflated; moulded
on the sidewall.
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N
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Normal Load
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Weight the tire can support in accordance with its size and
recommended tire inflation pressure.
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O
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Over-Inflation
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Too much air in the tire, resulting in premature wear in the middle
of the tread.
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P
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Passenger Car Tire
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Typically boasts extended life, comfort and all-season traction.
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Plus-Sizing
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Option allowing drivers to customize their vehicles by mounting
low-profile tires on wider rims of one or two inches in diameter, usually for
enhancing vehicle performance, handling and appearance.
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Ply
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One of the rubber-coated layers making up the structure of a tire.
Plies are typically reinforced by textile or steel cords.
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Pneumatic Tire
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Tire designed to be filled with air.
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PSI
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Abbreviation for pounds per square inch.
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Pulling
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When a vehicle veers toward one side independently of the steering
wheel due to uneven wear of the tires, poor front- or rear-wheel alignment, worn
or incorrectly adjusted brakes.
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R
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Radial Tire
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Tire with plies arranged so that the cords in the carcass run at 90
degrees in relation to the longitudinal axis of the tread.
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Rim
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Part of the wheel onto which the tire is mounted.
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Rim Border
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Surface of the rim in contact with the bead’s side.
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Rim Diameter
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Range of the rim’s bead on which the tire rests.
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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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Force required to keep a tire moving at a consistent speed. The
lower the rolling resistance, the less energy needed to keep a tire moving.
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RPM (revolutions per minute)
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Number of revolutions of a tire on a distance of 1 mile. May vary
according to speed, load and inflation pressure.
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S
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Section Height
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Height of the tire between the rim and outer tread.
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Section Height with Load
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Height of the tire section in contact with the road.
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Section Width
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Distance between a tire’s outside sidewalls, excluding any
lettering or other inscriptions.
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Series
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Tires with the same aspect ratio or same relationship between the
section height and width.
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Service Code
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Digits and letters moulded on the sidewall indicating the load
capacity, load rating, and speed at which a tire can carry a load in specific
conditions. Also called load rating and speed rating.
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Shoulder
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The area where the sidewall and top meet.
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Sidewall
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Portion of the tire between the tread and the bead. Protects the
tire against impacts. Contains important information about the tire.
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Sipes
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Special slits inside the design block that open up when the tire
presses against the contact surface and close back to break water stress on the
road and put the tread in contact with the road and maintain grip; improves grip
on a wet or snow-covered surface.
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Size
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Includes tire width, composition, aspect ratio and rim dimensions.
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Snow Tire (also called winter tire)
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Tire whose tread design and rubber compound provide better traction
in snow and on ice; identified by the inscription M+S, M&S or M/S on the
sidewall. Quality snow tires display the RAC Mountain Snowflake symbol
indicating that they meet the performance standards in snow as set by ACIC.
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Speed Rating
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Alphabetical code (A-Z) assigned to a tire indicating the range of
speeds at which the tire can carry a load under specific service conditions.
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Static Balance
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When the weight mass is evenly spread around the axis of rotation.
Vibrations in the seat, floor or steering column are signs of static unbalance.
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Steering System
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The entire mechanism that allows the driver to steer his vehicle;
includes the steering wheel, steering column, steering gearbox, transmission and
wheel supports.
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T
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Tensile Strength
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Resistance of an object to stretching or breaking under the effect
of stress. The metal belts of a tire are distinguished by their tensile
strength.
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Tire (or tyre)
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Assembly of rubber, chemicals, fibres and metal, engineered with
precision and designed to provide traction, cushion road shocks and carry a load
under varying conditions.
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Tire Designation
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Alphanumeric code moulded on the tire’s sidewall specifying the
tire’s size, including width, aspect ratio, rim diameter, load rating and speed
rating. Most designations use the P-Metric system.
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Tread
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Portion of the tire in contact with the road. It is distinguished
by the design of its ribs and grooves. It provides grip under various
conditions, resists violent forces, wear, friction and heat build-up.
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Tread Depth
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Depth of useable rubber, measured in .32 in. On a new tire of 10/32
in. of rubber, there is 8/32 in. of useable rubber. Tires should be replaced
when the wear bars are visible at 2/32 in.
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Tread Width
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Portion of the tread design in contact with the road.
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Tread Wear Indicators
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Narrow strips, also called wear bars, that appear on the
tread of the tire when only 2/32 inch of tread remains.
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Tire Designation
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Alphanumeric code moulded on the tire’s sidewall specifying the
tire’s size, including width, aspect ratio, rim diameter, load rating and speed
rating. Most designations use the P-Metric system.
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UVWXYZ
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Under-Inflation
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Use of a tire without sufficient inflation pressure to support the
weight of the vehicle with its occupants and the extra load; may cause tire
rupture due to heat build-up inside the tire.
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UTQGS (Uniform Tire Quality Grading Standards)
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Tire information system issued by the US Government providing
consumers with grades (AA to C) on tire traction and temperature. Life
expectancy is usually graded between 60 and 700.
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Wandering (steering instability)
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Tendency of a vehicle to zigzag due to steering anomalies, worn
tires, poor alignment, crosswinds or roadway unevenness.
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Wheelbase
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Difference in distance between the front and back of a pair of
tires mounted on the same axle. Also, longitudinal distance of the centre of the
front wheel to the centre of the back wheel on a vehicle’s same side.
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