Tyre companies throughout the world are members of regional tyre manufacturer's associations (ETRTO for Europe), which establish tyre dimensions and tolerances, load carrying capacities and inflation pressures for the different tyre categories and sizes. The basic tyre and rim dimension nomenclature is explained below:

Outside Radius (OR): The radius of an unloaded tyre, mounted on its recommended rim and inflated to recommended pressure.

Section Width (SW): The width of the inflated tyre section, on the measuring rim, excluding any lettering or decoration.

Section Height (SH): The distance from the bead seat to the outer tread contour of the inflated tyre - at centreline.

Static Loaded Radius (SLR): The standing height from the road surface to the axle centre under nominal tyre load/inflation conditions.

Loaded Section Width (LSW): The width of the loaded cross-section.

Aspect Ratio: The section height (SH) expressed as percentage of the section width (SW).

Minimum Dual Spacing: The minimum recommended distance between centrelines of dual mounted tyres to avoid kissing in the flex area.

Rolling Circumference: The distance covered by one revolution of the tyre (in mm). The rolling circumference of a tyre is important for establishing the correct tyre slippage relationship on 4-wheel drive vehicles using smaller tyres on the front axle as well as assuring dimensional compatibility for tyres used in dual mounted applications.