[JRTJH]

What Cal just posted is a "wider vision" of what Tireman9 posted. People who "spend a career in the tire engineering business" tend to view "their aspect of the business" and lose some perspective of the other areas of design that go into the "finished product". That's not a "slam dunk" for any specific part of engineering, but rather a "reality of what happens"...

We're doing pretty much the same thing in this thread....

Take for example, two trailers that weigh the same 14000 pounds "GVWR" with 2500 pounds of pin weight, both are 38' long, but with different slide configurations and different floorplans....

Trailer 1 may be a "rear kitchen model" with the heavy appliances positioned along the rear wall, very close to centered (side to side), so there is no impact on "side balance". It may have opposing slides over the axles, roadside with a large entertainment center weighing about 300 pounds and the curb slide having theater seating weighing about 300 pounds. That trailer may very well have "nearly equal weight over all 4 tires"....

Now, take trailer #2: It may be a "center kitchen model" with a heavy, 16' "kitchen slide" on the roadside. It might have a 4 door LP/Elec refrigerator over the rear roadside tire with that same "heavy entertainment center" aft of the refrigerator and a large pantry, just forward of the refrigerator. That slide might place 1500 pounds of potential weight over the tires on that side of the trailer. Now, imagine a 12' slide on the curb side, with a light dining table and 2 chairs with 2 small recliners just aft of that, the total slide weighing 700 pounds.

When designing/engineering either trailer, a part of the design would be to weigh individual wheels and decide which tires are appropriate. One trailer may have all 4 wheels "equally balanced" and a 15% excess capacity could/be achieved with 225/80R16 LRE tires at 80PSI.

Conversely, the other trailer in this example may have the roadside tires loaded with 700 or more pounds and the rear tire on that side loaded with nearly all of that "unbalanced load"... In other words, the roadside, rear tire may be carrying 50% more weight than the opposing tire on the same axle and the roadside pair may be carrying "more than double" the excess weight that the curbside pair are carrying..... Because of that "roadside rear tire weight" this trailer may require 235/85R16 LRF tires to achieve the same 15% excess capacity, even though the other three tires may be "perfectly happy with smaller tires"....

Now, ALL tires on the same axle must be "the same size and aired to the same pressure" and for compliance, I've always seen all tires on a trailer aired to the same pressure at all tire locations.

So, even though we have, in this example, two identical weight trailers that are the same length with the same cargo capacity, they "could have" dramatically different tire loading, tire size requirements and tire pressure requirements....

For anyone to "crawl in a bubble and only look at a small part of the design and implementation" can't present the "whole picture for how one trailer can be very different than the same "outward appearance trailer" sitting next to it...

Each trailer is a unique and individual "implementation" and for us to try to "put all 14000 pound 38' trailers in the same "tire size and pressure" is just "simply impossible"... To complicate that further, when the owner's DW adds "38 pairs of shoes" to the front closet, and the "other owner of that same floorplan" is a bachelor who prefers to be barefoot" .... Well you get the idea....