Tyre profile width in inches. Inches are the most popular width format; in addition to it, there is also a designation in millimetres. Formally, 1 inch corresponds to 25.4 mm, but in fact the correspondence is not so strict: for example, the width of a 13 ”tyre in millimetres is usually 315 mm, not 330 mm. So it is best to convert millimetres to inches and vice versa using special tables.
As for the width, in this case it is indicated by the distance between the sidewalls of the tyre mounted on the disk and inflated (but not loaded). This is one of the parameters that determine compatibility with a particular disc: the tyre must be slightly wider than the rim. For the selection of rubber for specific disks in width, there are special tables.
Among modern tyres for trucks and buses, there are such standard width options:
6.5",
7",
7.5",
8.25",
8.5",
9",
9.5",
10",
11",
12",
13",
14". Tyres for special equipment and agricultural machinery (see "Intended use") may have larger sizes.
The load index characterizes the maximum weight under which the tyre can be safely operated. As in the case of the speed rating described above, this indicator cannot be exceeded, otherwise unpleasant consequences are possible, up to accidents. Also note that when selecting according to the load index, it is worth considering the distribution of weight along different axes of the vehicle. And it is worth considering the maximum possible weight when the truck is loaded, in accordance with what to select
truck tyres for heavy loads.
