Will you increase load capacity with higher Load Range?

The question of load capacity and Load Range gets asked a lot, so it seems to be a bit of a stumbling block for a number of RV owners. Here is an example:
"I need to replace the ST235/75R15 tires on my trailer. Currently have load range C tires which is sufficient for the maximum trailer weight when inflated to 50psi but allows almost no safety margin. I want to change to either load range D or E tires. My rims are only rated for 65 psi so if I went to the load range E tires I would only be able to inflate them to 65 psi. My question is this. Is there any advantage to a load range E tire used at 65 psi vs a load range D tire at 65 psi?"

Now just because he is asking about a 15" trailer application and considering a change from LR-C to LR-D it does not mean the general answer does not apply to others, even if they are considering a change from LR-G to LR-H on a Goodyear 295/75R22.5 Class-A tire.

Let me explain.

As some of you remember, I previously covered the fact that it is the air not the tire that carries the load. For those that still have doubts, here is a picture from a special test machine that measures force and delivers the answer in color. In this case, the lowest force is Blue which increases to Green, then Yellow and finally Red at the highest force. It is clear that the tire wants to be round because of the high inflation pressure but when you press the tire against a surface it becomes flat with  the highest force in the center of the tire. If it was the sidewall that carried the load, as some want to believe, then the Red (high force) should be at the outside shoulders.

Now when you go up in Load Range you are actually looking at the capability of the tire to carry more inflation pressure. Remember to gain in load capacity you need to increase the inflation. Years ago when tires used cotton for body cord we might have 4, 6, 8 or more layers or ply of reinforcement to retain the increased air pressure. Those increments provided steps in the Load/Inflation tables. Since the late 60's and early 70's when materials improved the actual number of ply decreased and the term Load Range was applied to those steps.

So going back to the original question, when increasing the Load Range you gain the possibility of increased load carrying ability but if you don't increase the actual cold inflation, the change in Load Range will not give you any increase in load carrying capacity.

BOTTOM LINE
The answer to the question is;
 He will gain a safety margin if he increases his inflation to 65psi with LR-D but if he stays at 65psi there is nothing further gained by going to LR-E as there is no difference in the capacity at 65psi.
The same thing would apply to the 22.5 example. When we look at the Goodyear tables we see that at 110psi both the LR-G and the LR-H are rated for 6,175# single or in dual application at 100psi they both are rated as 5,675#.

Special note: It is important that you look at the table on the web site of the manufacturer of your tires as not all companies give the exact same capacity number at every inflation level, even for the same size.

The tire was "Defective"

I see this statement or somethnig similar in many posts on various RV forums. The problem I have is that too often the person making the statement offers evidence to back up their claim.

 The mere fact that a tire failed, simply does not mean it was defective. If someone wants to make that claim they need to provide a plausable theory on which material componenet was made incorrectly or which part of the tire manufacturing process was done incorrectly in such a manner that it would result in a tire failing in that specific manner.

Most radial tires made today have about 20 to 25 different components.

 This Wikipedia page identifies nine major components

 Watch this video and you will see a manual process used for a farm tire.
 
Hankook has a nice graphic showing more steps in detail for radial tires
 
Here is a promotional video from Michelin. The part about automatic tire assembly is very similar to what you would see in just about any modern tire manufacturing plant making Passenger, Light Truck or TBR Truck/Bus-Radials .
 
You can see that from manual to fully automatic the steps are very similar. It doesn't make any difference who makes the tire as all tires share very similar construction features.
So now that you have a little better idea of how tires are manufactured Try this exercise. Identify a step in the process that could be done incorrectly on one tire or a small group of tires. The out of tolerance step or material needs to be close enough to spec to allow the tire to finish the manufacturing process and to also allow the tire to function properly for a few hundred or thousand miles but then this error must somehow cause the tire to suddinly cause the tire to come apart but first provide no warning and second leave no evidence of the out of spec part or material being present in the failed tire.

I think you will find that it is very difficult to have a material out of spec enough to function acceptable for a short time but then to catistrophically fail a few miles later and to also leave no physical evidence.

I am not trying to imply that mistakes are never made but since the manufacturing process makes tires and even the components in batches if a mistake is made it should affect all the tires in that batch which would be from a couple hundred to a few thousand. If in fact those defective tires somehow managet to pass through final inspection unnoticed and make it to the tire store where they are mounted on your RV I think you can see that in all likelyhood all the tires with the same defect would fail in identical manner.
If a group of tires fail and if dealers or owners report the fialures to NHTSA then there is a high probability that action would result.

There have been a few cases recently where thousands of tires were recalled because a small number had been found with a defect. What I haven't seen or heard about is a recall because a single tire failed.

When we see a single tire fail and it leaves evidence such as worn sidewall or melted polyester body cord

or fatigued steel body cord as seen on the right.

Tire engineers can be quite certain the failure was not caused by a manufacturing error but in fact the tire was operated under-inflated at highway speed for a few miles. Also when a tire has managed to perform satisfactorily for thousands of miles before failing it is again very unlikely because of a manufacturing error.

All to often those that jump to the conclusion that the tire must have been defective because they checked the air a few hours of days before the tire failed. These folk fail to realize that tires can fail with sidewall "blowout" in less than 5 miles of running at significant under-inflation.

Here is an example of a tire that had been run under-inflated in a controlled test of 3.9 miles at only 10 to 15 mph. You can clearly see the internal damage.

This tire still had 20% of the inflation needed to carry the load so it was not completely flat. That circumferential line is where the body cord would melt or fatique if the car had been driven at highway speeds and only a mile or two further. However dollars to donuts most people would say that since they had checked the air 100 miles prior to the failure the tire must be defective.