Front tire of motorcycle Battlecross X40 of the company Bridgestone. It is suitable for off-road driving, meaning it can only be used for off-road driving.

Its dimensions are 80/100-21. That is, it has a width of 80mm, a profile of 100, and can be mounted on a 21" rim. The profile in tires, meaning the height of the tire's sidewall, is always referred to as a clean number without a unit of measurement as it is a percentage of the width. For example, a 180/55 tire has a width of 180mm and a profile of 55, meaning it has a profile of 180 x 0.55 = 99mm.

The load index and the speed index are two other important characteristics of tires. Specifically, the load index is the maximum load under which the tires are expected to operate properly and is described by an integer number, which corresponds to kilograms, while the speed index is the maximum speed under which the tires are expected to operate properly and is described by a letter from the English alphabet, which corresponds to kilometers per hour. It should be noted that the maximum kilograms, corresponding to the load index, are referred to per tire.

Note: The maximum weight increases proportionally with the load index number, meaning that the larger the number, the greater the maximum operating weight of the tire. Similarly, the maximum speed increases as the letter of the speed index "increases", meaning that the speed index "S" corresponds to a lower speed than that of the "V" index.

In this case, the tire is 51M, meaning that the load index and the speed index are 51 and M respectively.