What is a Tire?

Understanding proper tire maintenance, selection and safety, starts with knowing the basics: What is a tire? What is it made of? How do tires work?

Tires are a driver's first and only contact with the road, transferring actions like steering, braking, accelerating and turning to the road surface. Regardless of the vehicle you drive, the actual contact area (patch) each of your tires has on the road is roughly the size of a postcard, a small amount, to say the least.

Anatomy of a Tire

Tires are made up of several different components*:

The Bead: A rubber-coated loop of high-strength steel cable that allows a tire to stay "seated" on a rim.

The Sidewall: Literally the "side wall" of the tire, this protects cord plies and features tire markings and information like tire size and type.

The Tread: This is where rubber meets road, providing strength, stability and above all else, traction to the road surface.

The Body: This is the tire itself, made up of several layers of plies. Plies, like polyester cord, run perpendicular to the tire's tread and are coated with rubber to help bond with other plies and belts to seal in air. Plies give tires strength and resistance to road damage.

Belts: Rubber coated layers of steel, fiberglass, rayon and other materials located between the tread and plies, criss-crossing at angles hold the plies in place. Belts provide resistance to punctures and help treads stay flat and in contact with the road.

The Inner Liner: This is the innermost layer of a tubeless tire that prevents air from penetrating through the tire.

Sipes: Sipes are special treads within the tread that improve traction on wet, dirty, sandy or snowy road surfaces.

* Beads? Sipes? You can familiarize yourself with Tire Terminology here.

Types of Tires

Like vehicles, not all tires are built the same. Depending on what you drive and when, tires are designed specifically to respond to weather, vehicle size and vehicle function. This aside, one of the best ways to select a tire for your vehicle is to understand tire specification markings - where to find them and what they mean.

Read on for more information and click here to watch our Tires video.

Summer Tires

Designed primarily for dry and some wet driving, summer tires are not built to perform well on snow and ice, or in cold temperatures. Summer tires are designed for hotter weather, providing maximum traction and resilience on the road.

Summer tire tread design ranges from orbital grooves, to complex directional patterns, promoting various levels of handling in summer driving conditions. Not sure which summer tire is right for your vehicle? Consider the following:

For most vehicles, the original tire size is a good guide in choosing new summer tires. However, you should take into account that the larger and wider the tire, the increased likelihood of hydroplaning. To help prevent this, choose a summer tire with directional tread design.

Winter Tires

The need for winter tires has been around for as long as vehicles have, however, with the advent of "all-season" tires, many drivers are unaware of the benefits of winter tires. Designed to provide effective traction in difficult winter conditions like snow, ice and sleet, winter tires feature a combination of specialized tread design and compounds that provides more effective traction in Canada's difficult winter conditions.

Selecting the right winter tires for your vehicle should be based on your driving style and purpose of your vehicle. It is important to learn how to read a tire's side-wall markings to be sure you choose the best winter tires for your vehicle. Having the right winter tires on your vehicle will offer optimal control and traction, while helping to maintain the vehicle's fuel-efficiency.

Other suggestions for choosing winter tires:

• Select a narrow winter tire: wider tires "plow" through snow.
• Determine the "Optional Winter Tire/Wheel Size" from your vehicle's base model. This means taking the base model equivalent of your vehicle and using its tire size as your winter tire template.
• Speak to your GM Goodwrench technician about wheels or rims.

Performance-wise, two important aspects of winter tires to consider are their speed rating and pressure rating. Most winter tires feature a Q-speed rating, which is lower than general use tires. Winter tires also have specific tire pressure requirements: colder weather will cause tire pressure to decrease, so it is crucial to check your tire pressure in winter more often than you do in summer. Check your owner's manual for the proper pressure for your vehicle's tires.

All-Season Tires

Perhaps the most economical type of tire is the "all-season" tire, because it is designed for year round use. All-season tires feature a blend of technologies that make use of different compounds and detailed tread configurations, designed for most driving conditions like snow, rain, heat, cold etc. It's the "almost" perfect tire because it offers a smooth, quiet ride, with exceptional handling in many conditions.

All season performance does not mean best performance, however. The trade-off is a loss of traction and compound stiffening anywhere below 7 degrees Celsius (44.6 F). Also, while all-season tires offer greater highway ride comfort, they are not as effective on snow as dedicated winter tires.

All-season tires come in two classes: Passenger Tires and Touring Tires. Passenger Tires feature a smoother ride and longer tread-life while Touring Tires offer low noise and enhanced handling characteristics.

Selecting the right all-season tire for your vehicle should be based on the climate as well as your driving profile. Manufacturers also make the selection process easier. Most all-season tires are branded M+S (Mud + Snow) on the sidewall. Others may feature Four Seasons icons.

Performance Tires

Once reserved for exotic sports cars with high horsepower engines, performance tires are now used in practically every type of vehicle, They are available in all shapes and sizes as well as for almost every category and for most conditions, like snow, cold and even dirt roads.

There are four main types of performance tires:

• Performance: Designed for drivers wanting to enhance the look and low-speed traction of their vehicles.
• High-Performance: Designed to enhance high-speed handling and stability.
• Ultra High-Performance: Designed for extreme performance and one of the fastest tires available on today's most sophisticated sports cars and sedans.
• Competition: Built for racing classifications. These tires, while street legal, are impractical for most users because of their racing compounds and groove-free design.

Performance tires offer drivers an overall increase in handling, cornering ability and traction, superior to their original equipment tires. Generally, treads are much shallower than summer, winter or all-season tires, and feature a greater contact patch on the road.

Truck Tires

Today's truck tire is available in several categories, each with its own set of performance specifications, depending on truck type:

• Utility: Features excellent wear characteristics and a staggered tread pattern for excellent snow and mud traction for on and off-road use.
• All-Terrain: Features multiple tread pattern, durable compound, and is Rubber Association of Canada (RAC) Snowflake approved.
• Highway Use: An all-season performer with enhanced compounds designed for smoother rides.
• Performance: Optimized for improved performance at higher speeds and better handling, braking and traction in all conditions.
• Off-Road: The most aggressive tread-design, built to power through mud, snow and silt.

Replacing tires on your truck is no more complicated than replacing those of a passenger vehicle. There are two factors, however, that you need to consider: load rating and tire pressure. Because of the larger and heavier workhorse nature of most trucks, these two areas become important points to consider. To verify maximum payload and tire replacement load ratings, always refer to your vehicle's specifications, not the tire's.

The Tire Glossary

Air Pressure: The amount of air inside the tire pressing outward on each square inch of tire, expressed in kilopascals (kPa), the metric designation for air pressure, or pounds per square inch (psi).

Alignment: The state in which all wheels on a vehicle are pointed in the optimum direction relative to one another.

All-Season Tires: Tires that are designed for use on dry and wet pavement and also provide traction on snow and ice.

Aspect Ratio: The percentage relationship of a tire's height to its section width. The most common is 75, with the range continuing downward (65, 60, etc.) to 35. Low aspect ratio tires are also referred to as low profile.

Balance: The state in which a tire and wheel spin with all their weight distributed equally.

Bead: A round hoop of steel wires, wrapped or reinforced by ply cords, that is shaped to fit the rim; it holds the tire onto the rim.

Belt: A rubber-coated layer of cords that is located between the plies and the tread. Cords may be made from steel, fibre glass, rayon, nylon, polyester or other fabrics.

Casing: The tire body beneath the tread and sidewalls.

Cold Inflation Pressure: The amount of air pressure in a tire, measured in kilopascals (kPa) or pounds per square inch (psi), before a tire has built up heat from driving.

Cord: The strands of fabric forming the plies or layers of the tire. Cords may be made from steel, fibreglass, rayon, nylon, polyester or other fabrics.

Contact Patch: The portion of the tread that makes contact with the road.

Friction: The force between the tires and the road surface that causes the tire to grip the road.

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

Highway Tires: Also called Summer tires; designed for wet- and dry-weather driving, but not for use on snow and ice.

Hydroplaning: A floating effect caused by tires losing contact with a surface covered with water.

Innerliner: The inner most layer of a tubeless tire. The innerliner prevents air from permeating through the tire.

Kilopascal (kPa): The metric unit for air pressure. (1 kPa = 6.8947 psi)

Load Index: An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of a tire.

LT: Tire sidewall marking indicating usage for "light truck."

Maximum Inflation Pressure: The maximum air pressure to which a cold tire may be inflated, and the number is found molded onto the sidewall. It is often different than the vehicle manufacturer's recommended operating pressure.

Overall Diameter: The diameter of the inflated tire, without any load.

Overall Width: The distance between the outside of the two sidewalls, including lettering and designs.

P: Tire sidewall marking indicating usage for "passenger vehicle".

Plus-Sizing: 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.

Ply: 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 or tread.

Pounds per square inch (psi): The imperial unit for air pressure.

Radial Ply Tire: A type of tire with plies arranged so cords in the body run at 90 degree angles to the centre line of the tread.

Rim: A metal support for a tubeless tire or a tire and tube assembly upon which the tire beads are seated. Often referred to as wheel or wheel rim.

Rim Diameter: The diameter of a tire rim, given in nearest whole numbers (e.g. 15 inches).

Rim Width: Distance between the two opposite inside edges of the rim flanges.

Rolling Resistance: 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.

Rotation: The changing of tires from front to rear or from side to side on a vehicle according to a set pattern; it provides even treadwear.

Section Height: The height of a tire, measured from rim to the outer tread.

Section Width: The distance between outside of sidewalls, not including any lettering or designs.

Shoulder: The area of a tire where the tread and sidewall meet.

Sidewall: The portion of a tire between the tread and the bead.

Sipes: Special slits in a tread that improve traction when the road surface is wet or has dust, dirt, sand, snow or other material on it.

Size: The combination of tire width, construction type, aspect ratio and rim size used in differentiating tires.

Skid: To slip or slide on the road when tires lose their rolling grip.

Snow Tire: Often referred to as Winter tires, a special type of tire with a tread and compound that gives better traction in snow and other extreme winter conditions.

Speed Rating: An alphabetical code (A to Z) assigned to a tire indicating the range of speeds at which the tire can carry a load under specified service conditions.

Tire: 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.

Tire Identification Number (TIN): A code molded into the sidewall of a tire signifying that the tire complies with Transport Canada requirements. The TIN includes an alphanumeric designator that can also identify the tire's manufacturer, production plant, date of production and brand.

Tire Information Placard: 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.

Tread: That portion of a tire that comes into contact with the road. It is distinguished by the design of its ribs and grooves.

Treadwear Indicator: Narrow bands, sometimes called "wear bars", that appear across the tread of the tire when only 1.5875 mm (2/32 inch) of tread remains for most vehicles.

Tread Width: The width of a tire's tread.

Traction: The friction between the tires and the road surface, or the amount of grip provided.

Uniform Tire Quality Grading (UTQG): A tire information system that provides consumers with ratings for a tire's traction (from AA to C) and for temperature (from A to C). Tread wear is normally rated from 60 to 620. Ratings are determined by tire manufacturers using government-prescribed test procedures and are moulded into the sidewall of the tire.

Wear Bars: See Treadwear Indicator.

Decoding Tire Markings

Typical Sidewall Markings

Knowing how to "read" a tire will help you identify and choose the correct tire for your vehicle. Regardless of type, all tires feature a set of identifiers on the sidewall, outlining size, speed rating, maximum rated load and inflation, tread wear, traction and temperature labelling, materials used and the Tire Identification Number.

GM Tire Performance Criteria (TPC) Number

TPC certification involves more than 20 critical performance tests:

• Force & Moment
• Residual Aligning Torque (RAT)
• Rolling Resistance
• Braking Traction
• Driving Traction
• Uniformity
• Noise
• Dimensions
• Mass
• Rev/KM
• High Speed
• Air Retention
• Electrical Resistance
• Automatic Mounting
• Endurance (ATE)
• Treadwear
• Chip/tear
• Groove Wander
• Ride & Handling
• Wet/Snow Handling

The TPC system facilitates tire replacement for GM customers on GM vehicles, meeting the same critical performance specifications of GM vehicle original equipment tires.

Tire Size and Construction

• Tire Type: Identifies vehicle type. P denotes passenger vehicle*; LT denotes Light Truck.
• Tire Width: Measured in millimetres. E.g. 215
• Aspect Ratio: The ratio of the height of the tire's cross-section to its width. E.g. 65
• Construction: R denotes radial, whereas B indicates a bias construction.
• Wheel Diameter: The greatest distance across the wheel from tread to tread, measured in inches. E.g. 15

* May also include pickup trucks and SUVs.

Load Index and Load Capacity

• Load Index: The maximum load in pounds (lb.) that the tire can support when properly inflated based on the Load Index Chart. E.g. 89
  
  

  Load Index	Pounds	Kilograms
  75	853	387
  76	882	400
  77	908	412
  78	937	425
  79	963	437
  80	992	450
  81	1019	462
  82	1047	475
  83	1074	487
  84	1102	500
  85	1135	515
  86	1168	530
  87	1201	545
  88	1235	560
  89	1279	580
  90	1323	600
  91	1356	615
  92	1389	630
  93	1433	650
  94	1477	670
  95	1521	690
  96	1565	710
  97	1609	730
  98	1653	750
  99	1709	775
  100	1764	800
  101	1819	825
  102	1874	850
  103	1929	875
  104	1984	900
  105	2039	925

  
  
• Load Capacity: The maximum load in actual pounds (lb.) and kilograms (kg) that the tire can support. E.g. 1300 lbs. or 580 kg

Speed Rating

• Speed Rating: Indicates the maximum service speed for the tire based in the speed-rating chart. E.g. " H " indicates a maximum tolerable speed of 210 km/h (130 mph).
  
  

  Rating Symbol	Maximum Speed (km/h)
  Q	160
  S	180
  T	190
  U	200
  H	210
  V	240
  * ZR W	270
  Y	300
  	Over 300

  
  
  

Uniform Tire Quality Grade (UTQG) Labelling

UTQG stands for Uniform Tire Quality Grading. Developed by the US Department of Transportation (DOT), all tires sold in Canada feature this identification number moulded into the sidewall of the tire.

Treadwear

Treadwear Grade: A comparative rating (E.g. 220) based on the wear rate of the tire when tested under controlled conditions by the manufacturer on a specified government test track. E.g. a tire with a 200 treadwear rating would wear twice as long as a tire with a 100 rating.

• More than 100: Better
• 100: Baseline
• Less than 100: Poorer

Traction and Temperature

Traction Grades: Identify the tire's ability to stop on wet pavement measured under controlled conditions by the manufacturer on specified government test surfaces of asphalt and concrete. The test is based upon "straight ahead" braking tests. E.g. Traction A

• AA: Very Best
• A: Best
• B: Intermediate
• C: Acceptable

Temperature Grades: Denote the tire's resistance to the generation of heat when tested under controlled conditions by the manufacturer on a specified indoor laboratory test wheel. Excessive temperatures can lead to tire failure. E.g. Temperature A

• A: Best
• B: Intermediate
• C: Acceptable

Tire Identification Number

All tires sold in Canada feature a Tire Identification Number, which provides retailers with information about when and where the tire was produced.

Example:

• B3 : Indicates the manufacturer and plant code
• CD : Tire size code
• E52X : Optional
• 2602 : Week and year of manufacture (in this example the 26th week of 2002)

The maple leaf symbol indicates this is a Canadian made tire and certifies that it meets all of Transport Canada's requirements.

All Season and Winter Tire Markings

• M+S (Mud + Snow): Indicates this is an all-season tire. Every all-season tire must carry this symbol. For more on all-season tires, click here
• Four Seasons Ico: Indicates this is an all-season tire. Sometimes used in conjunction with or instead of the M+S symbol. For more on all-season tires, click here
• Winter Symbol: Indicates that this tire has been specifically designed for severe winter conditions. For more on winter tires, click here