Understanding Tires Load Index vs. Load Range
The numbers you see on the sidewall of a tire, contain valuable details about the tire. The alphanumeric code holds in itself the complete description of the tires, which helps people decide whether a tire is suitable for their vehicle or not.
Tire Load Index Capacity
The load rating of the tire displays the weight a tire can carry. The product of the load capacity of a single tire and the number of tires determines the load carrying capacity of all the tires combined. The rating of 121 shows that it has a load capacity of 3,297 LBS. Multiply that by four tires (4 x 3,297 = 13,188 pounds) to get your vehicle's max load carrying capacity. Always remember to install tires that have a load index that is equal or greater than your original factory-installed tires.
What is the Load Range?
Load range is the older measurement standard of "PLY Rating." This refers to the construct of the tire, which is made out of rubber and cord layers referred to as “plies.” Historically, more plies meant a tire had a larger load carrying capacity, so manufacturers would count a tire’s plies and use this number to denote carrying capacity. However, the modern construction of tires uses fewer piles without sacrificing the carrying capacity. Therefore load range simply tells how tough the tire is and the allowable PSI. For example, an “E” load range indicates that a tire is equivalent to a 10-ply construction tire. In reality, this tire is not built with 10 plies, but rather one or two plies of equivalent strength.