Tire and Wheel Glossary

Modification of a vehicle’s suspension (the system that connects a vehicle to its wheels) so the angles of the tires make proper road contact.

Ratio, stated as a percentage, of a tire’s cross-section height to it’s width.

Refers to the tire with an interior and exterior half’s of the tread pattern differentiating.

Even weight spread across a wheel and tire. For balance to occur weights are attached to the wheel.

Space from the mounting pad to the rear edge of the rim.

Space from the mounting pad to the rear edge of the rim.

The brink of the rim that creates a closure between the tire bead and the wheel.

Bias tires with strengthening belts between the exterior plies and the tread.

Cords covered in rubber, situated between the plies and the tread. They help strengthen the tread, and help the tire keep its shape against various internal and external forces. The cords are made from steel, fiberglass, radon, nylon, polyester or various other materials.

A tire that is constructed with plies laid out in interchanging directions at angles that are approximately 30-40 degrees to the center line of the tire. The plies form an intersecting design.

A tire that is constructed with plies laid out in interchanging directions at angles that are approximately 30-40 degrees to the center line of the tire. The plies form an intersecting design.

The angle of the centerline of a tire and wheel comparative to entirely straight up.

There are two types of pressure when it comes to molding wheels; low pressure and counter pressure. Low pressure casting comprises of Pouring liquid into a mold, whereas counter pressure casting consists of sucking the metal into a vacuum. The counter pressure method decreases impurities producing a stronger wheel.

The angle of the vehicle’s steering pivot axis compared to entirely straight up.

The central opening on the back of the wheel that mounts the wheel properly. The opening is created in a way that exactly matches the hub for the wheels to be properly positioned.

A protective layer made of rubber and fabric inhibiting rubbing between cord body plies and the wheel.

Measurement of air pressure within a tire that has not been driven for at least 3 hours.

Various compounding formulas are used to achieve different tire features such as: heat and cold resistance, increased traction, etc., through the use of rubber, plasticizers, preserving materials, and ozone retardants.

Threads of nylon, rayon, polyester, steel or fiberglass that make up the belts and plies of the tire. Cords determine the strength of a tire and its weight carrying capability.

Centre of the tread.

Additional rubber around the sidewall of a tire. It is there to guard the side of the tire from damage.

The 10 digit code appearing after the DOT (Department of Transportation) description provides demographic tire information, manufacturer, tire line, and size.

When the tread is in contact with the road.

A wheel manufacturing method permitting the compression of an aluminum billet into an aluminum wheel, essentially producing a one-piece wheel that is stronger than others.

Indents in the tire tread, there to prevent hydroplaning and create a gripping effect.

A wheel with a center piece created to coincide with a vehicle’s hub diameter.

Rings made of plastic or aluminum are mounted on a vehicle’s hub prior to the wheel, ensuring the wheel is perfectly centered on the vehicle’s hub. The lack of hub rings creates the likelihood of receiving a vibration even if the wheel and tire composure are ideally balanced.

The loss of grip as a result of water on the road, since the water may collect under the tire’s footprint and make the tire lift up from the surface of the road. The speed of the vehicle, water depth and the tread pattern are all circumstances affecting the creation of hydroplaning.

A representative number of the maximum load a tire can support. The index number matches to the actual load carrying dimensions. Truck tires use a different system including letter codes to create a Ply Rating.

Marking that approves the tire for use in mud and snow. Approved by the Rubber Manufacturers Association.

Joining different tire sizes or models is not suggested since all four tires will react differently and create unpredictable situations. Occasionally performance vehicles may come with different front and rear tire sizes.

Installation of tires onto wheels.

The space between the surface of the installation of the wheel to the precise centerline of the rim. A positive offset implies that the mounting surface of the wheel is positioned in front of the exact centerline of the rim, or in other words tire assembly, making the tire closer to the fender. On the other hand, a negative offset implies that the mounting surface of the wheel is behind the actual centerline of the rim or tire assembly, causing the tire to extend away from the vehicle.

Inflating the tire over the recommended air pressure amount. Sometimes it may be done for higher quality performance, however, this has damaging consequences to the tires and puts stress on the suspension.

Specifies tire sizes by using the tread width, in millimeters, as well as the aspect ratio, type or tire construction, and the rim diameter in inches, all together producing a tire size, for example: P215/70R16.

Attachment of greater diameter rims to lower sized tires, while keeping the general tire diameter within 3% of the usual tire size. Anything above 3% will create issues with the transmission shift points, leading to an increased fuel consumption, as well as, may complicate the braking system computers which in turn, may eventually lead to a brake failure.

Layers of rubber coated cords that provide a tire with its strength, located between the tire tread and the inner liner.

See “Aspect Ratio”

See “Air Pressure”

Tires made with plies at 90-degree angles across the crown of the tire. Require belt plies to go around the exterior of the tire.

A practice common among trucks, when there is an application of new thread to an old casing.

Sections of the tread (made of rubber) that go around the exterior of the tire.

The width measurement between rim flanges

Moving a car’s tires in all directions, done periodically in a set pattern, to extend tread life and avoid unequal tire wear.

The measurement in-between the sidewalls of an inflated tire (not under load) at its widest point.

See “Aspect Ratio”

The area where the exterior edge of the tire tread meets the sidewall.

The area between the tread and the bead.

Smaller cuts in the tread of the tire, there to assist in repelling water from the top of the tire to improve wet traction. Additionally, sipes create piercing edges for traction on snow and ice.

Letters, such as H, Q, S-W, Z, that identify the high speed of the tire’s resilience, tested at speeds set ahead of time, and the outcome of these tests determine the tire’s speed rating.

A sticker that is often found on an inside door of the car that shows the car’s standard tire size, and its suggested tire air pressure.

When the front tires are closer together than the rear.

When the rear tires are closer together than the front.

Tread’s individual sections parted by horizontal grooves.

The space measurement from the tires top of the tread to its grooves.

A term used to express how long a tire lasts before becoming unusable, measured in km. May also be expressed as a percentage of the leftover thread.

The organization of sipes, grooves, and channels on the tread.

Applied primarily for racing purposes to increase tire robustness and performance by shaving some of the tread from a tire.

See “Tread Life”.

Thin rubber bars input into the grooves of the tread which state the tire’s legal wear out point. They become at level with the tread when 2/32″ of the tread is leftover, at which point the tires are ready to be changed to new ones.

Differs from the overall tire width by being narrower, as this is the width of specifically the tread, typically measured in millimeters.

A tire that has less air inside than the suggested air pressure for a specified load. May lead to poor tire performance and overall wheel damage.

Uniform Tire Quality Grading (UTQG), is a rating system created by the American DOT. It is intended to inform customers of the comparative performance of passenger tires. This rating system does not include winter tires.