Terms and Components

Size designations

Bias tyres

6.00(1) - 16(2) 4PR(3)
20(4) X 8.00(1) - 10(2) 4PR(3)
355(6) / 80D(5)  15(2) 6PR(3)

(1) Tyre width in inches
(2) Rim diameter in inches
(3) Ply rating
(4) Tyre diameter in inches
(5) Aspect Ratio bias construction
(6) Tyre width in millimeters

Radial tyres

9.5(1)  R(2)  24(3)  18P.R.(4)  154(5)/149(6)  M(7)

(1) Tyre width in inches
(2) Radial Construction
(3) Rim Diameter in inches
(4) Ply Rating
(5) Load Index in single fitment
(6) Load Index in dual fitment
(7) Speed Symbol

*PR (Ply Rating)

The word "Ply" refers to the number of cords which form the carcus of a tyre.When cotton cord was used the strength of the casing was shown by the actual ply of cotton cords.Today, the cord material has changed from cotton to nylon, steel and others, so the ply rating is used to indicate strength, and not necessarily the number of cord plies in the tyre.

Tyre profiles

The tyre profile is the section height expressed as a percentage of the section width. Where these are the same it is expressed as 100 series.

100 Series (Tyre height = Sectional width)
Example: 10.00 R20

90 Series (Tyre height = 90% Sectional width)
A shorter sidewall, retaining the original overall diameter, demands a larger wheel. Hence a 22.5" tudeless tyre to replace a 20" tubed.
Example: 12 R22.5.

80 Series (Tyre height = 80% Sectional width)
A wider tyre with a lower profile for improved stability.
Example: 315/80 R22.5

65 Series (Tyre height = 65% Sectional width)
Wide single tyres to replace duals, known as wide base tyres.
Example: 385/65 R22.5