Load Range & Ply Ratings

A tire’s most important job is to carry the load required of it, and the load range/ply rating branded on the tire’s sidewall indicates how much load the tire is designed to carry (at a specific pressure). Whenever changing tire sizes or from one tire type to another, it’s important to ensure the load index of the replacement tire is the same or greater than the original tire and that the new tire is rated to carry the load of the vehicle.

Passenger Tires

Since most P-metric passenger tires are manufactured in the standard load range, they will have nothing branded on their sidewalls or may be branded standard load and identified by an SL in their descriptions, as in P235/75R-15 SL.

Light load P-metric tires will be branded light load, and identified by an LL in their descriptions, as in P285/35R-19 LL.

Extra load P-metric tires will be branded extra load, and identified by an XL in their descriptions, as in P235/75R-15 XL.

Note: Only P-metric sized tires with 45-series aspect ratios or lower may be manufactured in a light load configuration. Light load tires are designed to carry less weight than standard load tires and have been developed for specific applications “typically when relatively large tire sizes are used as Original Equipment (O.E.) on relatively small cars or for Track & Competition DOT tires are used for racing applications.”

Light Truck Tires

Before load ranges were adopted, ply ratings and/or the actual number of casing plies were used to identify the relative strength with higher numeric ratings or plies identifying tires featuring stronger, heavier duty constructions. Today, the ply rating doesn’t indicate the actual number of plies used in the tire. It is simply a rating indicating an equivalent strength of earlier, bias-ply tires.

Light truck tires are often available in multiple load ranges, so the appropriate load range is identified immediately following the size’s rim diameter in Tire Rack’s descriptions.

LT-metric, LT-flotation and LT-numeric tires are branded with their load range (load range E or LRE) or their ply rating (10 ply rated) on their sidewalls and list their appropriate load range letter in their descriptions as LT245/75R-16 E, 7.50R-15 D or 31×10.50R-15 C. LT-sized tires featuring section widths of 305mm/12.50″ or wider have their maximum loads and cold tire pressures rated at reduced maximum load pressures.

Special Trailer Service Tires

Special trailer service tires are often available in multiple load ranges. The appropriate load range is identified immediately following the size’s rim diameter.

ST-metric sized special trailer service tires will be branded with their load range (load range D or LRD) on their sidewalls and list their appropriate load range letter in their descriptions as ST205/75R15 LRD.

How is the load capacity of a tire determined?

Let’s begin by reminding ourselves that it is not the tire that carries the load, but the air inside it. The tire is just the container for the air. So, if you need to carry more load, you need more air. You might accomplish that with a larger air chamber or by forcing more air molecules into the same size air chamber you’d normally use for a commercial tire with a lower load capacity. In other words, you might use a bigger tire or a tire running at a higher inflation pressure. Either way, the tire needs to be strong enough to handle the higher capacity. The traditional ways of defining this are “Ply Rating,” “Load Range,” and “Load Index.”

What is meant by “Ply Rating?”

In the early days of bias tires, casing strength was built up by adding layer upon layer of cotton fabric. The layers were placed with the thread in each layer at an angle to each other. That added strength, because the tensions would be distributed throughout the layers of fabric. The Ply Rating used to refer to the number of layers of cotton.

Why aren’t there any odd numbers? Since you have to have at least two plies to have a “bias” arrangement, bias ply tires always had an even number of plies. Is cotton still used? Cotton went away a long time ago. One of the major improvements was making plies out of nylon. Nylon is so much stronger that if you’re old enough, you may remember seeing your tires stamped with the words, “2 Ply/4 Ply Rating.” That meant there were only two nylon plies, but they were so strong the tire was equivalent to one made of four cotton plies. And that’s about when things started to get complicated. How so? Ply materials continued to improve, especially with the introduction of steel ply materials and radial construction, making the old Ply Number less and less meaningful. And that resulted in the newer designation we use today, called “Load Range.” On the chart, you can see how today’s Load Ranges correspond to the older Ply Rating system. 

Ply Rating Load Range

• A 2
• B 4
• C 6
• D 8
• E 10
• F 12
• G 14
• H 16
• J 18
• L 20

And why isn’t there an “I” or a “K” Load Range?

Just to avoid confusion. An “I” might, depending on the typeface, look like the numeral “1″ and “K” is a very common abbreviation for “kilo” meaning “thousand.”

What does Load Range really mean?

Load Range indicates the maximum load recommended for the tire. This varies by tire size and inflation pressure: A bigger tire can hold more air and can be rated for a higher load. Also, a given tire size at a higher air pressure results in a higher-rated load.

Load Capacities for Some “G” Load Range Single Tires

And here are the same tire sizes, but in a higher load rating:

Load Capacities for Some “H” Load Range Single Tires

So what’s the difference between tires of the same size but different load ranges?

It’s no longer the number of plies. Most radial truck tires, for example, have a total of five plies. There’s one steel body ply and four belts under the tread. What is different today is the strength of the steel cables in those plies or the number of cables per inch. We’re now at the point where we no longer add more and more plies, but instead, adjust the strength of the entire casing to achieve the desired load capacity.

Will a tire with a higher Load Range last longer?

It might, but it also might not. What usually determines tire life is the rate at which the tread wears and whether or not the tread wears evenly. Or how many retreads you can get from its casing. As long as the tire has enough load capacity for the maximum load you will be putting on it, buying extra load capacity may not increase your tire life.