What do different numbers and letters mean on the sidewall of the tire? (for example tire size 205 / 55 R 16 94 T XL)

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