Tyre terminology

Here are a few tyre terminologies every automobile owner should be familiar with.


The mechanical adjustable components within the vehicle’s suspension. When a vehicle is in car alignment, the caster, camber, toe-in and thrust settings are set to specification. (Alignment article).

All Season Tyres

Tyres designed to provide good traction in a wide variety of road conditions, including wet, dry and mud. This design also limits the tyre’s performance in extreme conditions.


A term for describing the size of a tyre (H78-15, for example) where both letters and numbers are used.

Aspect Ratio

A term that describes a tyre’s height-to-width proportion. If a tyre’s sidewall height were 65% of its section width, its aspect ratio would be 65. In the tyre size expressed as 205/65-15, the number 65 is the aspect ratio. (Tyre Dimensions article)


The state in which a tyre and car wheel alignment assembly spins with all its weight distributed equally. A wheel balancer is used to place weights compensating for static and dynamic imbalances that exist in all assemblies. Not balancing an assembly can result in vibrations. (Tyre Balancing article)


A round hoop of steel wires, wrapped or reinforced by steel cords, placed at the very inside of the tyre’s diameter. (Tyre Construction article)

Bias Ply Tyre

A pneumatic tyre is manufactured in such as way that the plies are laid at alternate angles less than 90 degrees to the centerline of the tread. These criss-cross plies give the tyre its strength, but generate heat during operation and limit the tyre’s wear and performance.


The tyre body beneath the tread and sidewalls; also called the casing.

Contact Patch

The portion of the tread that contacts the road during operation.


The strands of material forming the plies or layers of tyre. Cords may be made from fiberglass, rayon, nylon, polyester or steel.

DOT Markings

Each tyre has a necessary Department of Transportation number imprinted on at least one of its sidewalls. That number begins with the letters “DOT” and may contain up to 12 additional numbers and letters.

The first and last digits are the most important for the tyre owner. The first two letters/numbers identify the manufacturer of the tyres. Prior to the year 2000, the last three digits of a DOT number represented the week (two digits) and the year (one digit) of production.


The portion of the tyre that makes contact with the surface of the road.


The resistance of one material (the tyre tread) as it moves against another (the road); this is the force that causes the tyre to grip to the road.

Gross Vehicle Weight

The actual weight of a vehicle when fully loaded with passengers and cargo.


The space between two adjacent tread ribs; also called tread grooves.

Heat Cycling

A method of “breaking in” competition tyres prior to initial use. Heat cycling gradually heats the tyre in a controlled environment to gently stretch the tread compound, resulting in better traction and longer tread life.

Highway Tyres

Also called summer tyres; designed for dry and occasional wet weather driving, but not for use on snow and ice.


A skimming effect caused by tyres losing contact with a surface covered by water.


The innermost layer of a tubeless tyre, which prevents air from permeating through the tyre. This thin layer of material replaces the innertube.

Load Index

An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of the tyre.

M+S, M/S or M & S (Mud and Snow)

Indicates that a tyre can reach particular standards for performance in mud and snow conditions. The tyre must meet the Rubber Manufacturers Association (RMA) definition of a mud and snow tyre.

Maximum Inflation Pressure

The maximum air pressure to which a cold tyre may be inflated; found molded onto the tyre’s sidewall.

OE and OEM

OE means “Original Equipment” and refers to the tyres included with a new vehicle at the time of purchase. “OEM” stands for “Original Equipment Manufacturer.”

Overall Diameter

The diameter of an inflated tyre without any load.

Overall Width

The distance between a tyre’s outside sidewalls, including lettering and designs.

P Metric

Uniform designation of tyre sizes in metric measurements originally introduced by American tyre manufacturers in 1977. Commonly called “P-metric series.” A typical P-metric tyre size is P215/70R-15.


A small label typically located on the edge of the driver’s door or inside the glove compartment of a vehicle. A placard contains information on the vehicle such as the manufacturer’s recommended tyre inflation pressure, seating capacity, and Gross Vehicle Weight (GVW).


An option allowing drivers to customize the appearance and performance of their vehicle by mounting lower profile tyres on larger diameter wheels. One-inch greater wheel diameter is referred to as plus-one, two inches is plus-two… and so on. Using a lower profile tyre with a greater diameter rim allows the overall diameter to remain about the same. (Plus Sizing article)


A rubber-coated layer of fabric containing cords that run parallel to each other; extends from bead to bead and goes between the innerliner and belts of tread.

Ply Rating

This letter indicates the load carrying capacity of the tyre in terms of its construction. A “C” indicates the tyre has a 6-ply load carrying capacity. The tyre is not actually built with 6 plies, but contains one or two plies of equivalent strength. A “D” is an 8-ply rating, and an “E” is a 10-ply rating. If there is no letter, the tyre has a standard 4-ply rating.


Pounds Per Square Inch. This is the standard unit of measurement for air pressure within tyres.

Radial Ply

Tyre construction where the cords in the body run at 90 degrees to the centerline of the tread.

Ride Matching

A system of balancing a tyre and wheel assembly using a simulated road test. Ride matching provides optimal weight distribution and eliminates vibrations caused by the combination of minor errors within tyres and wheels. (Ride Matching article)

Rim Width

Distance between the two opposite inside edges of the rim flanges.

Rolling Resistance

The force required to keep a tyre moving at a constant speed. The lower the rolling resistance, the less energy needed to keep a tyre moving.


Moving tyres from side to side or front to rear on a vehicle in a prescribed pattern to achieve uniform wear on all tyres. Rotations should be performed regularly every 6,000 miles. (Tyre Rotation article).

Section Height

The height of a tyre measured from the rim to the outer tread. (Reading the Tyre Size article)

Section Width

The distance between outside sidewalls, not including any lettering or design. (Reading the Tyre Size article)


A numerical representation of a tyre’s aspect ratio. For example, 60 Series indicates the tyre’s section height is 60% of its section width (See Aspect Ratio).


Wobbling of wheels from side to side on a vehicle. Improperly balanced tyres, misalignment and bent wheels can cause shimmying.


he part of a tyre where the sidewall and tread meet. Certain tyre design features shoulder blocks for better traction.


The part of the tyre between the tread and the bead.


An expression that defines a particular tyre in terms of its width, height, rim diameter, aspect ratio and construction type. 205/65R-15 expresses tyre size using the metric system. For more detailed information, visit our page on reading the tyre size. (Reading the Tyre Size article).

Snow Tyre

Also referred to as a winter tyre; a special type of tyre with a tread and compound that gives better traction in snow. Identified by M&S, M+S or M/S on the sidewalls. All season tyres also include these designations on the sidewall. (Winter Tyre FAQ).

Speed Rating

The speed rating of a tyre is based on U.S. Government standards for reaching and sustaining a specified speed. Typically, a tyre with a higher speed rating results in better handling. Speed ratings are determined via laboratory tests that simulate road performance at various speeds. Tyres are assigned a single letter (such as H or V) to designate speed rating. (Speed Rating article).

Tyre Pressure Monitoring System (TPMS)

TPMS is an automated system that monitors the air pressure in a vehicle’s tyres. When air pressure in one or more tyres drops 25 percent or more below the correct pressure, a warning alerts the driver.


The friction between a tyre and the road surface; the amount of grip provided.


The part of the tyre that comes into contact with the road. The tread type is distinguished by the design of its ribs and grooves. (Tyre Construction article).

Tread Depth

The distance measured in the major tread groove nearest the centerline of the tyre from the base of the groove to the top of the tread. According to law, most states legally consider a tyre to be worn out when it reaches a tread depth of 2/32″.

Treadwear Indicator

Narrow bands, sometimes called “wear bars”, that appear across the tread when 2/32″ of tread remains.

Tread Width

The width of a tyre’s tread.

UTQG (Uniform Tyre Quality Grading)

A tyre information system that provides consumers with ratings for a tyre’s traction (AA to C) and temperature (A to C). Treadwear is a numeric rating. Ratings are determined by tyre manufacturers using government-prescribed test procedures, and are molded into the tyre’s sidewall. These ratings can only be compared within specific manufacturer’s tyres and cannot be compared from one manufacturer to another. Our treadwear, traction and temperature page explains this rating system in much more detail. (Treadwear, Traction, and Temperature article).


A device mounted in the wheel that lets air in or out of the tyre. Valves include caps to keep out dirt and moisture and a valve to prevent air from escaping.