Tire Glossary Terms


A drivetrain that employs two differentials and a transfer case to provide power to all four wheels of a vehicle.

All-Season Tires

Tires designed to provide good traction in winter snow and slush without wearing too quickly on dry roads.

Aspect Ratio

Determined by the unloaded sidewall height of the tire divided by its overall width. A lower aspect ratio implies a shorter, wider tire.


All-wheel drive. A drivetrain that employs a front, rear and center differential to provide power to all four wheels of a vehicle.


The juncture at which a tire starts to skid during braking.

Plus Size Wheels

Wheel and tire packages that are larger in diameter than those included in a vehicles standard equipment. Also known as "up-sized wheels."

Spare Tire

A fifth wheel and tire that is stored on or in a vehicle for use when one of the four tires in use becomes disabled.


The distance from the center plane of one wheel to the center plane of its opposing wheel.

Tread-Wear Index

A tire rating that consists of a number followed by two letters (i.e. 300AB). The number indicates the useful life of the tire, the first letter indicates its traction in wet conditions (A being the best), and the second letter indicates its resistance to heat buildup.

Wheel Width

The distance of a wheel from bead to bead.

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