What do different numbers and letters mean in the side of the tyre? (for example 205 / 55 R 16 94 T XL)

The first three numbers (205) indicate the width of the tyre tread in millimeters. 60 is the aspect ratio or profile of tyre. This is indicated in percentage of the tyre width. “R” stands for the construction method of the tyre indicating the tyre is a radial tyre. The following two numbers (16) indicate the diameter of the wheel rim in inches. The next two or three numbers (94) indicate the load index of the tyre. In the example, 94 means the tyre can carry 670kg. of weight when the car is doing the maximum speed set for the tyre. The last letter (T) is the speed symbol. In the example “T” indicates that the maximum speed for the tyre in 190km/h with maximum weight and ideal air pressure.