Width
The first set of numbers on the tyre reading is the width of the tyre in mm. So here the tyre width would be 205mm.
Height
After the slash is the height/profile ratio as a percentage of the width of the tyre. In this case it would be 55. This number is calculated by dividing the tyre’s section height by the tyre’s section width, so if the tyre has an aspect ratio of 55, the tyre’s height is 55% of its width.
Rim Size
The next set of numbers after the tyre construction letter, represents the inner diameter of the tyre rim in inches. In the example, the diameter of the tyre rim is 16 inches.
Speed Index
The final letter of the tyre code represents a speed rating, which is the maximum speed that the tyre can handle while correctly inflated and under load. The letter displayed will vary, often between Q and Y. In this example, V means that the maximum speed is 149 mph.
The 91 refers to a load index table which states how much weight the tyre can carry at the permitted speed.