The speed rating code is made up of either one or two letters, or one letter and one number. It indicates the maximum permitted speed that the tire can sustain for a ten minute endurance without being in danger.
|Speed Symbols||Speed Category||Open-ended |
|Z||over 149||over 240|
|(W)||over 168||over 270|
|(y)||over 186||over 300|
Tires with a speed rating higher than 186 mph (300 km/h) are indicated by a Y in parenthesis. The load rating is often included within the parenthesis, e.g. (86Y).
In many countries, the law requires that tires must be specified, and fitted, to exceed the maximum speed of the vehicle they are mounted on, with regards to their speed rating code (except for "Temporary Use" spare tires). If a tire is replaced with a lower speed rating than originally specified by the vehicle manufacturer, this may render the vehicle insurance invalid.
Speed ratings apply only to the tire, not to the vehicle. Putting a speed rated tire on any car does not mean the car can be operated at the tire's rated speed.