The mechanical condition of adjustable components within the vehicle's suspension. When a vehicle is in alignment, the caster, camber, toe-in and thrust settings are set to specification. Severe impacts (hitting potholes or curbs) and worn suspension parts are the leading causes of misalignment.
A term for describing the size of a tyre (195/55R15 for example) where both letters and numbers are used.
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 205/65R15, the number 65 is the aspect ratio.
The state in which a tyre and wheel 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 vibration
A round hoop of steel wires, wrapped or reinforced by steel cords, placed at the very inside of the tyre's diameter.
Bias Ply Tyre
A pneumatic tyre manufactured such 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.
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.
Each tyre has a required 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. For example, if the last three digits are 439, the tyre was produced in the 43rd week of 1999.
Tyres produced after January 1, 2000 have a four digit date code at the end of the DOT number. The first two digits represent the week of production and the last two digits represent the last two digits of the year of production. So, 3500 as the last four numbers indicates that the tyre was produced in the 35th week of the year 2000.
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 the adjacent tread ribs; also called tread groooves.
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.
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.
An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of the 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. The vehicle's manufacturer selects these tyres to provide the optimal performance based on the performance characteristics of the vehicle. "OEM" stands for "Original Equipment Manufacturer."
The diameter of an inflated tyre without any load.
The distance between a tyre's outside sidewalls, including lettering and designs.
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 P205/55R16.
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.
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.
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.
Tyre construction where the cords in the body run at 90 degrees to the centerline of the tread.
Distance between the two opposite inside edges of the rim flanges.
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 10,000 km.
The height of a tyre measured from the rim to the outer tread.
The distance between outside sidewalls, not including any lettering or design.
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.
The 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. 205/65R15 expresses tyre size using the metric system. For more detailed information, visit our page on reading the tyre size.
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.
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.
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".
Narrow bands, sometimes called "wear bars", that appear across the tread when 2/32" of tread remains.
The width of a tyre's tread.
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).
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.
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.