Glossary of Common Tire Terminology
Bead: The element that holds the tire onto the rim, composed of a round hoop of steel wires that is shaped to fit the rim and is reinforced or wrapped by ply cords.Belt: A layer of cords that is coated in rubber, found between the tread and the plies.
Casing: The body of the tire under the sidewalls and tread.
Cold Inflation Pressure: How much air pressure is within a tire before the tire has heated up from driving. Measured in psi or kPa.
Cord: The fabric strands that form the layers or plies on a tire.
Contact Patch: The area of the tread that touches the road.
Friction: An elementary force that is created between the tire rubber and the road surface that causes the tire to grip the road, as when braking or accelerating.
Groove: The space lying between the ribs of two adjacent treads.
Highway Tires: These are summer tires, meant for dry or wet road conditions, but not meant for driving on snow or ice.
Hydroplaning: The event of drifting that occurs when tires lose contact with the surface of the road, typically occurring during very wet conditions.
Innerliner: The innermost layer of a tubeless tire, which seals in the air and keeps it from permeating through the tire membrane.
Kilopascal (kPa): The metric unit which measures air pressure. One kilopascal is equal to 6.8947 psi.
Load Index: A number that defines the load carrying capacity of a tire, ranging from 0 to 279.
LT: The designation for Light Truck found on the tire sidewall.
Maximum Inflation Pressure: The upper limit to which a cold tire may be safely inflated. This number is typically found on the tire sidewall, and it often differs from the vehicle manufacturer’s recommended pressure setting.
Overall Diameter: Measure of the diameter of the inflated tire without any load.
Overall Width: Measure of the distance spanning between the exterior of the two sidewalls, including designs and lettering.
P: The designation for Passenger Vehicle, molded onto the tire sidewall.
Plus-Sizing: The option available to drivers to mount low-profile tires on wider rims, usually between one or two inches greater in diameter, in order to enhance the performance, handling, and overall look of the vehicle.
Ply: A layer of fabric coated in rubber containing cords running parallel to each other, which goes between the inner liner or tread (or belts0, and extends from bead to bead.
Pounds per Square Inch (psi): The imperial measure of air pressure.
Radial Ply Tire: A special tire design in which the plies are arranged and ordered so that the cords in the body extend at 90-degree angles towards the center of the tread.
Rim: A metal support used by tubeless tires on which seats the tire beads. It is often alternatively referred to as the wheel or wheel rim.
Rim Diameter: The length spanning the tire rim, in inches, rounded to the nearest whole number.
Rim Width: The measure between two opposite inside edges of the rim flanges.
Rolling Resistance: This is the energy, or force, that is necessary in order to keep a tire moving at a consistent speed. The lower the amount of force necessary, the less energy required to keep a tire moving.
Rotation: The process of removing and alternating tires within a vehicle to ensure even tread wear.
Section Height: The measurement from the rim to the outer tread of a tire, which measures a tire’s height.
Section Width: The distance across the tread between the outside of the tire’s sidewalls, not including lettering or molded designs on the sidewalls.
Shoulder: Where the sidewall and tread meet.
Sidewall: The area between the bead and the tread.
Sipes: Special slits that are designed into the tire tread in order to maximize traction in adverse road conditions.
Size: A term to describe a tire’s width, aspect ratio, construction type, and rim size combined, used in order to differentiate between tires.
Skid: To lose traction and slide across the road when tires lose their rolling grip.
Snow Tire: Interchangeable term with Winter Tires, a tire with a special composition and deeper tread enabling them to perform better in cold, snowy, and icy conditions.
Speed Rating: A code used to specify the speeds at which a tire can carry a load under specified service conditions, ranging from A to Z.
Tire Identification Number (TIN): An alphanumeric code that is found on the tire sidewall that indicates plenty of data, including brand, manufacturer, production plant, and date of production, which also demonstrates that the tire complies with Transport Canada requirements.
Tire Information Placard: A tag permanently affixed to a vehicle that lists the proper tire size and air pressure for the vehicle, as well as its load capacity and the size of its rims.
Tread: The ridged and grooved part of the tire that is in contact with the pavement.
Treadwear Indicator: Occasionally referred to as “wear bars,” these are narrow bands that span the tread of the tire that only begin to appear once just 1.5875 mm (1/16 inch) of tread remains for most vehicles.
Tread Width: A measurement of the distance across the tread of the tire.
Traction: The grip provided by the friction between the tires and road surface. Higher traction is preferred in slippery or rough road conditions.
Uniform Tire Quality Grading (UTQG): This is the government-prescribed information system adhered to by tire manufacturers for use of the consumers. It rates tires for traction (AA to C), for temperature (A to C), and for tread wear (60 to 620), and is listed on the tire sidewall.
Wear Bars: Markings on the tires that help identify the level of wear on a tire, used to help determine when a tire replacement is in order.
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