Load Index Ratings
Beginning in 1991, the U.S. Department of Transportation required that service descriptions be placed on all tires, excluding those that are Z-speed rated. The overall tire service description is imprinted on the sidewall of a tire. It consists of a two or three-digit number followed by a letter and can be found immediately after the tire size. The letter portion of the tire description represents the speed rating of that tire. Tire load index is the numerical portion of the tire service description.
Load index ratings range from 71 to 125. The number is not the load capacity of the tire; it must be correlated using a chart like the one below to determine the maximum load rating. Load index ratings are based on the maximum allowable fill pressure of the tire, as listed on the sidewall.
Let’s consider the following tire size as an example: 215/60 R16 94V. In this case, 94V is the Service Description. 94 is the load index rating, and V is the speed rating. Based on the chart below, the 94 corresponds to a load index rating of 1477 lbs at maximum tire pressure, so the load-carrying capacity of all four tires would be 4 x 1477 lbs = 5908 lbs.
It is important to note that the maximum load capacity of the tires may not be the actual capacity since the air pressure in the tires will probably be set by the manufacturer at a level below the maximum air pressure listed on a tire’s sidewall. The total vehicle weight must be factored into the equation when determining the optimal tire from a load-rating perspective.
For safety reasons, the industry recommendation is that a driver should not replace a lower load index rating than the Original Equipment Manufacturer tires specified by the manufacturer. In fact, due to liability concerns, most installers will not sell nor install a lower load rated tire than the OEM recommendation.