The load index refers to the load-carrying capacity of a tire, or how much weight a tire can support. For example, if a tire has a load index of 89, it can support 1,279 pounds (from below chart) at maximum air pressure. Multiply that by four (4 x 1,279 = 5,116 pounds) to get your maximum load-carrying capacity. It is not recommended to install tires with a lower load index than what came on your car from the factory.