I recently found a discussion on tire 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:
The load Range is rated at “H” 4940# single tire. That’s at max pressure!!
Load Range 4675 Dual tires.
The tread is 5 ply of steel. Good puncture protection with 5 steel treads.
The 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???
Strength of steel ply in tires
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.
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 maximum 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?
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 “strength” 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 wanted a “G” rated tire, then they would ask the engineer to change the 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.
An example in a tire I developed
I can relate this to 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.
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”.
Roger Marble
Check out my Blog www.RVTireSafety.Net
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Thank you, Roger. Your columns make me extremely cautious with our tires and how we load our motorhome; thank you!
I went from “D” rated tires to “E” rated tires on my TT years ago. I understand if I wanted to go higher I’d have to check the rating of my wheels and maybe get a whole new set of wheels. Correct?
That would be correct. “E” rated tires generally have a max inflation pressure of 80 PSI and, if your trailer came with D or E rated tires, the wheels would likely be rated at 80 lbs. as well. If you look at the back of the wheels there should be the weight rating stamped into the metal. You may have to wipe the dirt away to see it though. I did have one fifth wheel that came with E rated tires on 110 lb rated wheels, so when I changed to G rated tires I didn’t have to change wheels. Well worth it to check.