It seems this will be a never ending task of explaining the "Why and How" of setting tire pressure on RVs.
A. Trailers should follow the placard which is probably the tire sidewall pressure unless the size or type has been changed. BUT they should also confirm that no individuakl tire is overloaded due to un-balance.
B. Motorhomes should run the tire placard inflation unless they know the actual load on each tire.
C If a Motorhome owner knows the actual corner load he should consult the load inflation charts from the tire manufacturer for his brand in RV use. Select the inflation needed to exceed the actual load of the heaviest side of each axle and then inflate all tires on that axle to the minimum inflation plus 10%
D, If the tires on the trailer have been changes then the individual loads for each tire need to be known. Using load inflation tables select a tire with sufficient Load Range to carry that load and then set the cold inflation to the inflation shown on the tire sidewall.
Following the above should decrease the damage done by running a tire in overload and under-inflated condition. Hopefully this will also prevent Tread separations and Blowouts.
Here is a recent post on a thread titled "Calculating the correct tire pressure". This forum is 95% trailer oriented.
"A while back, we weighed our travel trailer on the CAT scales and got a
total weight of 7,300 pounds, rigged for towing. Rigged for towing
means with a full water tank, all of the misc. junk that we normally
carry and weight distribution bars tensioned, but no clothing or food on
board. On average, this translates to 1,825 pounds per tire.
Today, we were able to obtain individual wheel weights using portable scales. The results are (rigged for towing)
Left Front - 2,000 pounds Left Rear - 1,900 pounds
Right Front - 1,900 pounds Right Rear - 1,700 pounds"
We can immediately see the unbalance in this trailer with the heavy tire having 27% of the total. We also learn that the TT was not fully loaded with food or cloths which would add more weight. We also see that when the owner simply used the original CAT scale weight he assumed equal weight distribution of 1825# per tire.
In this case the owner was not aware of the special loading seen by trailer tires.
In this same thread we found one owner that switched from ST235/75R15 LR-D to P23575R15/XL ! giving up about 23% of the load capacity. This thread is at 85 posts and counting.
Clearly the need for more knowledge on care and maintenance of tires in RV application is needed. I hope I have provided helpful information here and in my seminars. Please spread the word. If you have a specific question you can send a question to Tireman9 at Gmail dot com