Tire terminology: Basic tire construction, Part 2

I have previously covered basic tire construction as you would find in most passenger car tires and lower cost, lightweight RV trailer tires. I had some additional questions, so I have expanded the information.

As we move on to larger, heavier trailers, pickups and Class A, B and C motorhomes, what I would expect to see is tire constructions with 1 or 2 body ply + 2 or more steel belts + 1 or more "cap ply". The differences would also be larger and stronger reinforcement materials.

NOTE: the details of the "Cap Ply" are not listed other than the number and generic material such as "Nylon" or "Aramid".  THE KEY IS THAT AT LEAST SOME CAP PLY IS SHOWN".

IMO no cap ply shown, indicates to me an ST type tire in Load Range C through E to be avoided for multi-axle trailer use. 

For those who skipped over the "lesson" on tire construction, we are reviewing the material list as seen on the sidewall of all tires, similar to what might be seen in this picture:

OK, but what about Load Range E or F or even G and H Load Range tires? What's the difference?

I found a discussion on 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 is an example of what you might see on a Class-A tire sidewall:
Load Range is rated at "H" 4,940# single, 4,675# Dual tires.
Tread is 5 ply of steel. Sidewall is 1 ply of steel.

"Strength" of steel ply in tires

Well, I feel that a better understanding of the "strength" of the steel ply might help people understand the concept of different tire constructions.

The steel in tires is not a single strand of steel, as you find in a paper clip, but a twisted cable of many smaller strands or filaments of steel. The number of "ply" or layers of cord (textile or steel) are not in itself 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 strengths. Also, the number of strands and even the "twist" of the strands can affect the strength and flexibility in the end product. Some examples of just a few of the hundreds of different steel cables I might select when designing a tire can be seen in this post.

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.

The MINIMUM "strength" of your tires would be the load range—required to support NO LESS than the truck scale reading for your RV when it is fully loaded. (Load capacity of 110% of scale reading would be better.)

Do not try and get information on the twist or cabling of the steel in your tires. You can simply use the load range letter and load capacity numbers where higher is stronger.

You need to be careful of who you listen to when purchasing RV tires

OK, my intent is not to try and turn you all into Tire Design Engineers, but to help you appreciate that tire design is a complex topic that is seldom covered in sufficient detail in an RV Forum. Also, I want to allow you to decide on what you need to consider when purchasing tires for your RV application.

I hope that you can see that you may need to review numerous posts to learn what you need to consider when selecting different tires than what were originally provided.

I seldom see posts on tires that include the "complete" tire type and size information. When people run out and purchase tires without understanding the needs for their specific RV, there is a good chance that they may end up having to rely on a "salesperson" who has insufficient knowledge to ask the basic questions about your RV tire usage. You probably need to be better educated on your tire needs than any tire salesperson you will run into.

Be careful when trying to rely on RV Forum posters. I am only aware of two actual Tire Engineers on any of the dozen RV forms out there. I do know of at least one person who thinks they know more about tire design and performance characteristics than the tire companies do, but that person consistently provides misleading advice to the RV community.