Tire Load Index Vs. Ply Ratingby Theresa Custodio
The tire load index, also called the load range, specifies the amount of weight the tire can safely carry when inflated to its optimum pressure. Prior to the adoption of current industry load standards, the ply rating indicated the number of fabric layers coated in rubber that made up the body of the tire. Today, the ply rating is a strength comparison based on previous standards for bias ply tires.
Load Ranges -- Passenger Vehicles
Passenger vehicle tire load ranges are rated as light, standard or extra load. The load range of a tire is identified by the letters "LL" molded into the sidewall meaning light load, or "XL" for extra load. Standard load tires generally contain either no letter designation or the letters "SL" on the sidewall.
Load Ranges -- Light Trucks
Load ranges for light truck tires are labeled by a letter from the alphabet molded into the rubber, with "A" indicating the lightest load capability. As the load range letters move closer to "Z," the amount of weight the tire will withstand increases.
Load Range Tire Pressures
Recommended tire pressure increases as the tire load range moves higher. Light and standard load tires for passenger vehicles require 35 psi of inflation, with the extra load range calling for 41 psi. Light truck tire pressure begins with 35 psi for "B" labeled tires and increases 15 psi for each letter through the letter "F."
Theresa Custodio is a Michigan-certified nurseryman with over 10 years experience. She has spent over five years working for the State of Michigan's Department of Environmental Quality writing permits and violation notices, which are published for public record. She has a Bachelor of Science degree from Eastern Michigan University with a major in biology and a minor in conservation and resource use.