What Does Ply Rating Mean in Tire Talk? Ply Rating vs. Load Index

The ply rating of a tire in the 20th century referred to the layers of cotton fiber stretched within a tire that directly affected the tire’s durability and capability to bear heavier loads. There’s a bit of discourse in the tire community about the term “ply” because it’s a little outdated. Today, advanced engineering allows for materials that don’t require multiple plies to get the same strength. If you want to learn more about the plies of a tire and how they’re used today, read more about bias plies, also known as cross-ply tires. 

You may also recognize the term “ply” … from toilet paper! Toilet paper’s strength and durability is also measured in plies, which is how many layers of material are contained within a square of toilet paper. So, 2- or 3-ply toilet paper won’t rip and tear as easily, but it also will cost you more. 

“Ply rating” has stuck around as a term that’s correlated to a tire’s load rating. Some tires still have a ply rating while others use the direct term “load range” instead. 

A 10-ply tire, for example, doesn’t actually have 10 layers of fiber within its construction. But the materials within its construction are strong enough to bear a very heavy load, similar to a tire that would have 10 plies. Maybe you’re starting to see why this term is falling out of favor. 

So how do you know the ply rating of a tire?

How to Find a Tire's Ply Rating

You won’t find a ply rating on most modern tires. Instead, look for the load rating of a tire. Tires have codes on the sides that give you information about their construction, capabilities, and ratings. Knowing how to interpret these codes allows you to make a more informed decision about what type of tire to purchase. 

The load rating will be found near the end of the code on a tire. Load ratings are essentially an equivalent term for ply rating. Load ratings speak straight to the point about the tire’s capability to carry heavy loads. A tire with even a single ply of strong material can have high load ratings. 

In the past, ply rating was measured in the aforementioned "layers' (as in 4-ply, 6-ply, 8-ply, 10-ply, etc.). You can read our article on tire load indexes to know how to interpret the load rating code on the side of your tire. 

Once you have a better understanding of tire load index, below, you’ll find a rough equivalence of ply to load ratings. If you’re already familiar with ply ratings, this chart may be helpful to you. 

Ply Rating Chart

This chart is ply ratings and their equivalent load ratings:

As demonstrated here, each letter increase is about the same as an increase in plies. The load ratings indicate the maximum PSI that your tire can be at max load. For example, a C1 tire has a max PSI of 50 at max load, whereas a C2 tire has a max PSI of 35. The max PSI will increase the higher the load rating is (with standard being the lowest and G being the highest). 

Of course, this isn’t the whole picture. After all, what’s the max load of your tires? What’s the carrying capacity of your tires? Tire load indexes are a more updated and useful measurement that give you information on the carrying capacity and recommended speed of the tire. It’s still useful to know the load rating of a tire, as it informs what the PSI of your tire should be, but the tire load index is a more complete picture. 

You should have a clearer understanding of why ply ratings were previously used but are becoming obsolete now. While some tire distributors and manufacturers (and our customers) may still use the term, it’s pretty easy to convert ply ratings to load ratings. Remember that ply ratings step up by 2 and with each step ascend the alphabet. 

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