What does "L" refer to in the following tyre designation: 315/80 R 22.5 156/150 L?

The letter "L" in the tyre designation indicates the maximum permissible speed of the tyre according to its speed rating. Each letter corresponds to a specific maximum speed the tyre can safely handle. In this case, "L" means the tyre is rated for a maximum speed of 120 km/h.

This speed rating is important because it tells you the fastest speed at which the tyre can operate safely under its recommended load conditions. Using tyres with the correct or higher speed rating for your vehicle ensures safety and optimal tyre performance.

Load-bearing capacity and air pressure tolerance are indicated by other markings, such as the numbers before "L" (which represent load indexes) and pressure specifications, but "L" specifically relates to speed.