What does the numerical speed letter rating on tires mean?

[VonJames]

The meaning of the numerical speed letter rating on tires: Different tires have English letters on their sidewalls indicating the speed rating of the tire, which denotes the maximum speed at which the tire can carry a specified load under defined conditions. The letters corresponding to the tire speed rating represent certified speed ratings ranging from 4.8 kilometers per hour to 300 kilometers per hour. JKLMNPQRSTUHVWYZ are the letters corresponding to the speed ratings of radial tires, where J to Y represent 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 240, 270, and 300 kilometers per hour respectively, and Z represents speeds above 240 kilometers per hour.