Although they give you a general description of what a tire can do, it can be difficult to understand exactly what tire codes and descriptions mean. Load specifications are one major area of confusion. Many people ask “What’s the difference between ‘Load Index’ and ‘Load Range’? They’re both an indication of how much weight the tire can handle, right?” Well, yes and no.
Load Range Is Based on ‘Ply Rating’
A tire’s ‘Load Range’ can be found on the tire’s sidewall represented by a letter, usually after the tire size (35X12.50 R17/E for example). This code represents the ability of the tire to hold air and weight; the higher the load range (A→G) the heavier load the tire can carry.
Load range measurement is based upon an older metric called ‘ply rating.’ To understand ply rating we must first understand that tires aren’t made of just rubber; inside the tire, sandwiched within the rubber are cord (metal and fabrics) layers that are called ‘plies.’ Although tire technology has advanced to the point where the number of plies doesn’t have as much impact on the tire’s ability to withstand heavy loads, tire manufacturers historically used the number of plies in a tire to determine its load range with more plies meaning a higher load range/load capability.
Each letter increment (A to B, B to C, etc.) meant the addition of two more plies, so a tire with Load Range A had two plies, while a Load Range E tire had ten. Today, a Load Range A tire is said to have the equivalent of two plies and a Load Range C has the equivalent of six. That Load Range C tire these days probably only has one or two plies though, thanks to technology.
Modern tires, especially those designed for commercial use may have an alphanumeric Load Range classification such as C1 or C2. The C still means the tire has the strength of a six ply tire and the number denoted the tire’s max pressure rating. A C1 tire can support the same weight as a C2 tire where the C1’s max pressure rating is 50 PSI and the C2’s pressure is cut to 35. A tire with the numeric suffix 1 will always have a higher max inflation pressure than the same load rating with the suffix 2. See chart below for Light Truck tires1.
Light Truck Load Ratings
Max Tire Pressure (PSI) @ Max Load
1 Passenger tires are unmarked and considered to have a four ply rating and may be marked either standard load (SL) with a max inflation pressure of 36 PSI or Extra Load (XL) with a maximum inflation pressure of 42 PSI at maximum rated load.
Load Index Indicates a Tire’s Maximum Carrying Capacity
With the almost obsolescence of the Load Range/Ply Rating metric, tire makers have begun using a new measurement system known as Load Index. Load Index is a numerical system that indicates a tire’s maximum load carrying capacity at the maximum inflation pressure. Load index values range from a low of 70 to a high of 110 for passenger cars. This index goes to zero (0) to incorporate smaller tires for wheelbarrows, trailers, riding lawn mowers, etc. See the chat below.
Load Index and Carrying Capacity
Dan the Tire Man would be happy to help you with any questions you may still have about tire Load Range and Load Index and which tire would be a perfect fit for your vehicle and driving style.