Load inflation tables identify the minimum inflation for a number of specific load placed on the tire.
Tire sidewalls tell you the maximum load capacity for a given tire when
inflated to the maximum pressure for that load range in that size tire.
Optimum implies we have common agreement on which performance requirements we feel are most important. Optimum also implies that there is agreement in the inherent trade-offs of the numerous performance characteristics.
If the only performance we are concerned about is load capacity
and if we want the maximum capacity possible for the size and load
range of a specific tire, then we have a situation where the optimum inflation is the maximum for the load range, which is also the minimum inflation specified in the tables.
If, however, we do not need to support a load that corresponds to the
tire's maximum load, then it is possible that other performance criteria
may be considered and as a result there will be trade-offs to arrive
at a new optimum.
If we are talking about motorhomes, there are normally performance
characteristics other than just load capacity. Some might be fuel economy, noise, ride comfort, tread wear, steering response, etc.
Inflation pressure will affect each of these characteristics — some
positively and some negatively. So clearly the "optimum" depends on the clearly understood and agreed on priority of these and other characteristics.
As a tire engineer I suggest that people select an inflation pressure
that will provide at least 15 percent extra load capacity over the heaviest
loaded tire on an axle. All tires on an axle should run the same cold
inflation. The above will still provide acceptable ride and provide improved durability and fuel economy.
For multi-axle trailers I would consider improved durability, i.e., reduced chance of failure, to be of primary importance. So in this application, the "optimum" inflation pressure would be the pressure on the tire sidewall associated with the maximum load capacity. Even if you are not loaded to the max load you want to lower the "interply shear" forces as much as possible, as trailers induce much higher shear forces than seen in similarly loaded tires would if on a motorhome.
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