Technology Dimensions

Tire Terminology

Terminology Definition
Gross width The straight line distance between the sidewalls including lettering and the protect line on theside of the tire when the tire is placed on a fitting rim, is filled with the appropriate air pressureand has no load.
Section width The width without the protect line on the side and lettering.
Tread width The distance across the tread surface measured without load.
Overall Diameter The diameter of an inflated tire without any load.
Section height Tire diameter minus rim diameter, divided by 2
Rim diameter Straight line distance of the rim base in contact with the rim flange (almost the same as the inside diameter of a tire)
Rim width Distance between the two opposite inside edges of the rim flanges
Rim flange height Rim flange diameter minus rim diameter, divided by 2
Static loaded radius The shortest distance between the middle of the axle to the road surface; measured with the tire inflated to required pressure, and carrying 100% rated load.
Dual tire spacing Distance between center lines of dual tires
Overall Diameter The diameter of an inflated tire without any load.

(1) Aspect Ratio

The concept of a tire series is the same as the aspect ratio. A tire’s aspect ratio is the percentage that results from the section height divided by the section width multiplied by 100. The lower the figure, the greater a tire’s section width.
This means the tire becomes wider and safety increases when driving. As the figure increases, the tire’s section height increases, increasing the flexibility of the sidewalls and resulting in a smoother ride.
Accordingly, consumers seek the aspect ratio best suiting their needs but the current trend is for tires that have low aspect ratios for high-speed cars. Hankook Tire has developed the 25 series, a super wide series boasting the highest safety levels. Example) 60 series = (Section height / Section width) X 100 = 60

(2) Durability

A tire’s durability is designated by the ply rating (PR). A higher PR number indicates a greater load range for the tire. A similar term is body ply layers. When cotton cord fabric was used, the actual number of body ply numbers was indicated. However, the number of body ply layers has dramatically decreased due to the appearance of cord fabric such as high strength rayon, nylon and polyester. Consumers, who were accustomed to using a tire that had so many body ply layers, understood that the number of layers had decreased due to the high strength cord fabric. However, they began to ask how many layers of the old cotton fabric would correspond to one layer of the new fabric. In answer to their question, the ply rating (PR) came to be used. So while a 6-PR does not mean a tire has in fact 6 layers of body ply layers, the rating does indicate that the tire retains the same strength of having 6 body ply layers.

(3) Ply Rating

As an example, the ply rating (PR) can be indicated as 6-PR as well as the alphabet ‘C’ in load range.

Load range Ply rating Load range ply rating
A 2 G 14
B 4 H 16
C 6 J 18
D 8 L 20
E 10 M 22
F 12 N 22

Passenger Car Tire Marking

In the past, tire sizes were indicated using the metric, alphanumeric and numeric indicating methods but nowadays they have been replaced by the ISO (International Standards Organization) method.

Light Truck Tire Marking

5.50 - 13 1.0 6PR
7.50 R 16 1.0 16PR
185 R 14 102/ 100 N 8PR
Overall diamter Section width Aspect ratio Construction Nominal rim diameter Load index of single wheel Load index of dual wheel Max. speed Ply rating
31 x 10.50 15 R 15 109 Q 6PR
100 235/ 75 R 15 110 107 P 8PR

Truck and Bus Tire Marking

315/ 75 R 22.5 154/ 149 L
Section width Aspect Construction Nominal rim diameter Load index of single wheel Load index of dual wheel Max. speed Ply rating
11.00 . 20 149/ 146 J 16PR

Construction Tire Marking

30.00 R 51 230 B
17.5 R 25 176 A2
17.5 R 25 167 B
40/ 65 R 39 228 A2
Section width Aspect ratio Construction Rim diameter Ply rating Load index Max. speed
16/ 75 - 20 18PR 151 B
37.50 - 51 44PR 237 A2
37.00 - 25 28PR 174 B
605/ 80 R 25 188 E

Agricultural Tire Marking

7.50 - 18 6PR
11.5/ 70 - 16 14PR
20.8 R 38 153 A8
Section width Aspect ratio Construction Rim diameter Load index Max. speed Ply rating
520/ 75 R 34 145 A8
210/ 70 - 15 2PR
230/ 95 R 48 140 A2