Term Definition
Air pressure The level of pressure in your tires, usually measured in pounds per square inch (PSI). The PSI value shown on the sidewall of the tires is the maximum amount of pressure the tire can hold, not the recommended value. For the recommended PSI for your vehicle model, please consult your owner’s manual or vehicle placard 
Alignment The process of realigning a vehicle’s suspension to ensure that tires wear evenly. Uneven tread wear can lead to shorter tire life.
Aspect ratio Tire sidewall height as a percentage of width. In the tire size 205/55/R16, for example, 55 is the aspect ratio. It indicates that the side wall of the tire is 55% as large as the tire width (205) in millimetres.
Backspacing The space between the mounting pad and the back of the wheel.
Balancing The process of ensuring all tires are balanced so the load of the vehicle is being distributed evenly.
Bead The edge of the tire that sits on the wheel.
Belts Internal bands that surround the inside of the tire to provide rigidity when the tire contacts the ground. Belts can be made of steel, Kevlar, polyester or twaron.
Bolt pattern A measurement showing the number of bolt holes in a wheel and the diameter of the circle formation on which the bolt holes are placed. For example, a 5-114 bolt pattern is a wheel with 5 bolt holes placed in a circle, with a diameter of 114mm. Each vehicle model requires a specific bolt pattern for wheels to be installed correctly. 
Camber The angle where the tires stand relative to the road. Can be positive or negative.
Centre bore The centre opening of the wheel that centres the wheel on the vehicle’s hub.
Chafer Strips that reinforce the beads and protect the bottom edge of the tire from rim friction or damage when replacing the rim.
Cold inflammation pressure The recommended inflation pressure of your tires before the car is driven and the tires are warmed. See your car owner’s manual.
Compound The chemical formulation of the tire. Tires are made of a combination of rubber and various other materials, based on the purpose of the tire. For example, winter tire compounds are designed to stay soft in cold temperatures.
Cords The cords are the main reinforcement materials for the tire. They help provide ride support and comfort.
Curb Guard Extra rubber on the rib of the tire meant to protect the tire’s internal sidewall and the wheels on which they are mounted. 
DOT Also known as the Tire Identification Number (TIN). A 10 to 12 digit number on a tire’s sidewall, the DOT represents the plant where manufactured, the size, pattern, brand of tire and date it was manufactured. 
Flange The flared edge of the barrel on both the inner and outer sides of the wheel. It helps prevent the tire from slipping off the wheel.
Footprint/contact path The patch of the tire that contacts the road. Performance tires have a short and wide footprint, while light truck and passenger tires have a long and narrow contact patch.
Forged Form of wheel construction. Allows for a reduction in wheel weight while boosting structural rigidity vs. a standard cast wheel.
Grooves The grooves in the tire, which allow water to expel under the tire, to maintain traction on wet roads and prevent hydroplaning. 
Hub centric (Direct fit) One of two types of aftermarket wheel rims. The hole in the centre of the rim is an exact fit on the vehicle.
Hydroplaning (Aquaplaning) The skidding or sliding of car tires across wet surfaces. Hydroplaning occurs when the tire floats up on top of water and loses contact with the road. 
Load index A classification related to the tire load carrying ability measured in lbs/kg for single back wheel vehicles. Based on industry standard code table. 
Lug centric (multi fit) One of two types of aftermarket wheel rims. The centre hole is oversized to fit a wider range of vehicles. Vehicle-specific hardware is used to affix the wheel to the vehicle.
M+S A tire sidewall mark seen on all season tires indicating that it has been approved for use in mud and snow by the Tire and Rubber Association of Canada (RAC). This should not be confused with “Snow Peak” rated; the mark on the sidewall of a tire that indicates it is approved by the government for winter use. M+S tires are not considered winter tires under Quebec Winter Tire legislation.  
Max inflation pressure The maximum inflation pressure the tire can handle. This is indicated on the sidewall of the tire and is measured in PSI.
Mixing tires Replacing two new tires instead of four. This practice is not recommended. Instead, use four identical tires on your vehicle.
Mounting The process of putting a tire onto a rim.
Offset The offset of a wheel is the distance from the hub mounting surface to the centre line of the wheel. The wheel offset is measured in millimeters and results in a positive, negative or zero offset.
Open tread design A style of tread pattern that is designed to help evacuate water and slush from road surfaces. 
Over inflation When the tire is inflated beyond the recommended PSI level of the vehicle. Leads to a shortened tire lifespan and uneven tread wear.
Piles The plies are the inflexible elements of the tire that provide structural support and strength to the sidewalls and tire.
Radial tire One of the two classifications of tires. Construction allows for a softer ride, flexible sidewalls and better fuel economy. 
Ribs The rubber elements of the tire tread that contact the road.
Rim width The minimum or maximum of the range of wheel rim width that the tire fits.
Rotation The process of moving a vehicle’s tires and wheels to allow for even tire wear. Wear differs, as the weight at the front and back of the vehicle differs.
Run flat A tire that can be driven on while flat, for a limited distance at reduced speed.
Section width Width of tire measured in millimeters or inches from sidewall to sidewall.
Shoulder The side of the tire between the tread centre and sidewall. It provides support and protection to the tread and sidewall. Its thick rubber makeup enables the tire to hold its form when turning.
Sidewall The side of the tire that has markings on it indicating its key characteristics: Vehicle class, Nominal section width, Aspect ratio, Fabric carcass construction, Required wheel diameter, Load index, Speed Rating
Sipes The tiny slits in the tire tread. They help enhance a tire’s grip and performance on wet pavement and icy conditions by creating more biting edges.
Speed rating A classification of the maximum speed the tire can be driven within safety limits. For example: M = 130 km/hr, N = 140 km/hr, and P = 150 km/hr. The speed rating of the vehicle also has an impact on the handling of a tire – it is recommended that you maintain your vehicle’s original speed rating.
Tire placard Located on the inside of your door. Shows vehicle tire size and recommended tire pressure for front and rear tires.
Tire blocks The independent tread elements on the outside edge of the tire, which go around the tire and enhance handling.
Tire depth Original manufactured vertical distance measured from outside edge of tire tread to bottom of deepest tread valley. When a tire has only 4/32nd of an inch of tread left, you should consider replacing your tires. At 2/32nd, your tires are considered legally bald.
Tread pattern The pattern of tread on the tire. Patterns differ based on the type of tire and its purpose. 
Tread wear The tread pattern on tires wears out over time from the impacts of the road. Therefore, checking your tread depth on a monthly basis is necessary. Tires with low tread depth remaining will start to lose performance in snowy and wet conditions.
Tread shaving The process of shaving off tire tread to ensure uniformity across all four tires.
Under inflation Occurs when your tires are not inflated up to the recommended PSI for your vehicle. Leads to reduced stopping, braking, handling, and premature tire wear.
UTQG A tire rating system used in the U.S. that provides an overall rating for a tire based on its tread wear, traction and temperature grading. Ratings are relative to other tires made by the same manufacturer and cannot be compared across manufacturers.
Wheel weights Weights placed on the outer and inner flanges of the wheel. Used to balance out the weight of the vehicle to enable a smoother ride and more even tire wear.