The size of a tire must satisfy some basic conditions.
The bead diameter must suit the wheel rim diameter.
Section width must be suitable for use on the wheel rim, and large enough to have a suitable load-carrying capacity for the vehicle.
The overall tire size must allow sufficient clearance between the tire and the vehicle frame.
All manufacturers mold information about the tire into its sidewall.
In cross-ply tires, the bead diameter and the section width are stated in inches. For example, six hundred by sixteen indicates a tire with a section width of 6 inches and a bead diameter suitable for fitting to a rim which is 16 inches in diameter, across the bead seats.
The load capacity is indicated by the ply rating, for example, 6PR.
The aspect ratio of a tire is the ratio of its height to its width. It is usually given as a percentage. The lower a tire’s aspect ratio, the wider the tire is in relation to its height.
An aspect ratio of 98% means the section height of the tire is slightly less than the section width. This is called a cushion or balloon tire.
An aspect ratio of 88% means the height is 12% less than the width, giving a lower profile. It is called a medium low profile tire.
The profile of cross-ply tires was reduced further to between 78 and 82%, called a super low section. However the stiffness of cross-ply tires makes them unsuitable for further reduction in profile.
Radial ply tires have been manufactured in 78% profile, but are also made with further reductions in profile, from 75%, to 45%.
