Two types of the tyre size designation can be found on a tyre sidewall, a tyre width expressed in mm and the tyre width expressed in inches.
1. The tyre width expressed in mm
All tyres for the commercial vehicles must be marked with a Service Description
located after the size designation (European regulation ECE-R54). The service description consists of load index
and speed rating
(e.g. 156/150 L).
Listed below are a few examples of the truck/bus tyre size designations.
Here is an example of the tyre size designation for commonly used truck tyre:
Designation: 315/80R22.5 156/150 L (154/150 M)
The designation meaning:
- 315
- The tyre width (the nominal section width) expressed in mm.
- 80
- The aspect ratio (the ratio of sidewall's section height to the tire's section width) in % (80%).
- R
- The construction code (the radial construction).
- 22.5
- The rim diameter in inches.
- 156/150
- The load index for single and dual fitment.
- L
- The speed rating - the tyre's maximum speed. See the speed index table.
The load index indicates the maximum tyre load capacity for single and dual fitment. The first number: 156, means that the maximum tyre load carrying capacity is 4000 kg for the single fitment. The second number: 150, indicates the maximum load carrying capacity of 3350 kg for the dual fitment. See the load index table.
For e.g., a tyre with the load and speed index of 156 L is designed for the load of 4000 kg and the maximum speed of 120 km/h.
The tyre manufacturers have the option of marking tyres with an additional load/speed index for an alternative higher speed or load. That code may be placed in a circle near basic designation (e.g. 154/150M).
The tyre size presented below is common on the buses:
Designation: 295/80R22.5 152/148 M
The designation meaning:
- 295
- The tyre width (the nominal section width) expressed in mm.
- 80
- The aspect ratio (the ratio of sidewall's section height to the tire's section width) in % (80%).
- R
- The construction code (the radial construction).
- 22.5
- The rim diameter in inches.
- 152/148
- The load index for single and dual fitment.
- M
- The speed rating - the tyre's maximum speed.
2. The tyre width expressed in inches
Designation: 11 R 22.5 148/145 L
The designation meaning:
- 11
- The tyre width expressed in inches.
- R
- The construction code (the radial construction).
- 22.5
- The rim diameter in inches.
- 148/145
- The load index for single and dual fitment.
- L
- The speed rating - the tyre's maximum speed.
Related articles:
- Tire size designation can be found on the tire's sidewall, see their meaning.
- Light trucks: vans, SUVs and light duty pickup trucks, have their own designations.
- Motorcycle tire size designations
- You may look up a speed index and adequate speed rating in the Tire speed rating table.
- Visit the page Load index chart and find out what is the load capacity of a tyre, based on its load index.