On modern tires, the Service Description can be found on the side of the tire next to the tire size. It will be a number letter code that refers to the load index and speed rating.
Load Index - a numerical code that is associated with the maximum load the tires can carry
Speed Rating - Made up of either one or two letters, or a letter followed by a number. This indicates the maximum speed the tires can sustain for a ten minute endurance without being
in danger.