Let's take a tire with size 225/50 R17 98H as our example. The 98H at the end represents the service description. The service description indicates the tire's load index and the speed rating. 98 is the load index and the H is the speed rating. Below you will see what each means and understand them. Since 1991, service descriptions have been required on all tires.
The load index is a numerical value used to identify the load carrying capabilities of the tire. The higher the load index, the greater it's load carrying capacity. Using 98 as our example load index, our tire has a maximum load capacity of 1,653 pounds.
The speed rating is a letter used to identify the maximum speed at which a tire will function properly. Using H as our example speed rating, our tire has a maximum speed of 130 miles per hour. Although the tire is capable of safely reaching these speed, it is highly recommended you drive at the legal speed limit.
It is important to note that these values apply only to tires that have not been damaged and are properly inflated. The actual speed rating and load index may change on road conditions, driving habits, and weather.