Tire ply rating and load range. What are they?

“What’s the difference in tire ply rating and load range? I just want the best ply.”

I found a discussion on “ply rating” aka load range in a forum where the question “How strong of a tire do I need?” was being discussed. Here is some of the discussion:

Below you see what is stamped on my tire sidewall:
Load range is rated at “H” 4940# single tire That’s at max pressure!!
Load range 4675 Dual tires.
Tread is 5 ply of steel. Good puncture protection with 5 steel treads.
Sidewall is 1 ply of steel. Maybe this is why they ride smoother with only 1 steel side wall.
Am I missing something since your load rating info is not the same as mine. There’s not enough plies to be rated an “H” tire???

I felt that a better understanding of the “strength” of the steel ply, in the subject tires, might help people understand the concept of different tire constructions.

“Ply” doesn’t necessarily indicate strength

The number of “ply” or layers of cord (textile or steel) are not in themselves any proof of strength. Individual cords of steel are made up of many strands. The steel or other material used to make the strands can have a wide range of strength. Also the number of strands and even the “twist” of the strands can affect the strength and flexibility in the end product. Here are some basic examples of steel cord/cable.

Each has a different configuration. Without more information it would be impossible to know which is “stronger.” Don’t forget tires have to flex and bend millions of times, so just max strength may not be the best choice as you need flexibility, too.

If we get to more complex cords, we “twist” cords together and can get different properties, as seen here:

How is the material selected by the tire engineer?

So an obvious question is, how is the material selected by the tire engineer?

There are a number of different tests conducted on tires to establish their overall rating and the different materials can help a tire meet the different tests. It is completely possible for a given tire to pass some tests associated with a given level, let’s say “G”. BUT if a given tire only passes the “F” level of one test, then the tire would be rated as “F” even if it passed the “G” level in the other tests.

Now, if the sales department already had an “F”-rated tire in the line-up and wanted to add a “G”-rated tire, then they would ask the engineer to develop a specification so the tire could pass all the “G” level testing. This change or “improvement” may or may not result in more layers of steel.

Tire ratings

I can relate an actual example of such a process in a tire I developed. It turned out in this case that the only change I needed to make was the wire in the “bead” of the tire. This is the “cable” of wire that holds the tire on the wheel. It is kind of an anchor for the body ply. Here is a very basic image of tire components. The feature I want you to understand is where the “bead” is located.

So, I selected a different configuration of bead wire and the new construction was able to pass all the standard tests to confirm a “G”-rated tire.

As you can see the “ply” can be very complex. Simply looking at the number of layers in the construction but not the load range can be misleading.

Need to know the load capacity

The bottom line is you need to know the load capacity in pounds that you need for your specific application. In the same size you may have different load range such as E, F, or G. Each load range has a different inflation level for the size tire you are considering and a different load capacity. So, you need to consider much more than just the number and type of “ply.”

Additional side note: The original poster commented on the “smoother” ride and incorrectly credited the one-ply in the sidewall. I am pretty sure that if you read the material list for a bunch of F-, G-, and H-rated radials you will soon note that they all have only one “ply” steel sidewall.

I don’t have a picture of the material list on the sidewall of an LR-G or H 22.5″ tire right now, but here one is from a regular 16″ LT radial.

Roger Marble

Check out my Blog www.RVTireSafety.Net

Read more from Roger Marble on RVtravel.com.

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