Tire & Wheel Information – Glossary of Terms

Having trouble with some of the more technical tire and wheel terminology? Browse our tire and wheel glossary and brush up on some of the more popular concepts in tire and wheel tech.

Air Pressure

The measure of force exerted by the air inside a tire, typically measured in pounds per square inch (PSI), or kilopascals (kPa).

Alignment

The correct angle settings of a vehicle’s suspension components. The 3 alignment settings are caster, camber, and toe.

Aspect Ratio

The relationship between a tire’s section height and its section width. It is calculated by dividing the section height by the section width. With the section height is half of the section width, the aspect ratio is 50. In a tire size description, it would be the 50 in “P195/50R15.” It is also referedd to as the tire’s profile or the series.

Asymmetric

When opposite sides of a tire’s tread pattern are not identical.

Backspacing

Also known as rearspacing, this is the distance from the mounting pad to the back edge of the rim. Not to be confused with wheel offset.

Balance

The even distribution of weight on a mounted wheel and tire.

Bead

The part of the tire in contact with the wheel flange. It is made of high tensile steel wires shaped to fit the rim and hold the tire on the wheel. The steel wires are wrapped in woven fabric and held in place by the plies.

Bias Tire

A tire constructed with plies laid out in alternating directions in angles about 30-40 degrees to the center line of the tire. The plies form a criss-cross pattern that is typically suited more towards off road driving.

Bolt Circle

The number of lug holes on the diameter of the imaginary circle that each lug hole is centered upon.

Bolt Pattern

The arrangement of bolt holes on a wheel. Some wheels have more than one bolt pattern on the same wheel to accommodate multiple fitments.

Camber

The angle of the centerline of a tire and wheel relative to completely vertical.

Cast Wheels

Wheels that are made from liquid metal poured into a mold. Low pressure casting involves pouring the metal into a mold, while counter-pressure casting involves sucking the metal into a mold like a vacuum. Counter-pressure casting reduces impurities to make the wheel much stronger than a low pressure cast rim.

DOT

DOT is an acronym that stands for Department of Transportation. The 10-digit code after the DOT designation provides information such as the week and year the tire was produced, plus the manufacturer, plant, tire line, and size.

Hub Centric

A situation wherein the center bore of the wheel is made to match up with the diameter of the automobile hubs; the wheel is then balanced by the center hold rather than the lug holes.

Hub Centric Rings (Hubrings)

Hard plastic or aluminum rings mounted on a vehicle’s hub before the wheel. This ensures that the wheel is perfectly centered on the vehicle’s hub, and also lessens the possibility of vibration when the tire and wheel are perfectly balanced.

Load Rating or Maximum Load

The most weight a tire is designed to carry. A tire’s load-carrying capacity is directly related to the tire’s size and how much inflation pressure is used. Listed maximum loads are rated with the tire inflated to an industry-assigned inflation pressure.

Offset

The distance from the mounting surface of the wheel to the true centerline of the rim. A positive offset means the wheel’s mounting surface is positioned in front of the true centerline of the rim and tire assembly, brining the tire into the fender well more. Conversely, a negative offset means the wheel is behind the true centerline of the rim and tire assembly, causing the tire to stick out away from the vehicle.

Overall Diameter

The diameter of an inflated tire without any load.

Plus Sizing

Changing the original stock tire size of your vehicle in order to enhance vehicle performance by allowing for fitment of larger wheels and tires. It is recommended that you keep the overall tire diameter within 3% of OEM tire size to prevent problems with transmission, gas mileage, and braking.

PSI

The most common measurement unit for tire pressure that stands for pounds per square inch. PSI is intended to measure the force exerted by the air inside a tire.

Radial Tire

Tires built with perpendicular plies across the crown of the tire, effectively strengthening the tread for street driving. These tires also require belt plies going circumferentially around the tire for solidarity purposes.

Rim Diameter

The distance between bead seat to bead seat at bead seat radius.

Rim Width

The measurement between the flanges of a rim.

Section Width

The distance between the sidewalls at the widest point of an inflated tire not under load.

Sidewall

The side portion of a tire between the tread and bead.

Sipes

Small slits in a tire’s tread that help push water away from the crown of the tire for improved wet traction. They also provide biting edges for ice and snow traction.

Tread Blocks

Raised rubber compound segments in a tire’s tread. Blocks of varying sizes, shapes, and designs are typically used for a variety of effects, such as better wet traction, or stronger rock-crawling ability.

Tread Depth

The distance from the top of the tread to the grooves in a tire. The measurement is taken at the centerline of a tire and is measured in thirty-secondths of an inch.

Tread Pattern

The arrangement of grooves, blocks, sipes, and channels on the tread of a tire that provide a varying degrees of effects on traction, tread life, and other tire factors.

Wheel Diameter

The measured distance that extends from one bead seat to another across a wheel. The wheel diameter must be exactly the same as the tire rim diameter. Always make sure that the diameter stamped on the wheel and tire match exactly.

Wheel Offset

The distance between the wheel mounting surface where bolted to the hub of the drum and centerline of the rim. This determines a vehicle’s “track,” or distance between tires on each axle. Keep the wheel offsets as close to original as possible to avoid steering and wheel bearing difficulties.

Wheel Width

The distance between the inside of the rim flanges rounded to the nearest half inch that helps to ensure that the wheel width is the appropriate size for your tire. Each tire has a minimum and maximum wheel width limit.

Zero Offset

A condition where the wheel’s mounting surface coincides with the centerline of the wheel.