You are correct, many folks INCLUDING dealers, do not use the up to date information regarding product.
First, tires are all about weight rating. Standard Big Country tires have a weight rating of 3,580lbs, when properly inflated. Yes, there is a difference in the amount of tire PLYS, however, the weight rating is something else entirely. Using the current tires, we are well within the 14,000 axles rating. GVWR or gross vehicle weight rating includes axles weight rating and hitch pin weight. TECHNICALLY, if you add up the twin 7,000 lbs axles AND the hitch weight, you will see that we are usually in the 16,000 + range. We underate our GVWRs to 15,500, due to the pin box weight ratings.
Goodyear LT235/85R16 ‘G’…..14 Ply
Towmax ST235/80R16 ‘E’…....10 Ply
Ply Rating and Load Range
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Ply ratings identify the load carrying capabilities of a tire in terms of plies. Ply rating originally referred to the number of cotton layers used to strengthen a tire’s casing. Today, when tires are labeled 10-ply, they are not actually constructed of 10 individual layers of cotton but offer the equivalent strength. Passenger tires are currently constructed from one or two body plies, while light truck tires consist of two to three, or one steel ply. Over time, steel ply and radial construction replaced cotton leading to a new distinction, load range.
Load range identifies the maximum amount of weight that can be placed on a tire horizontally, which varies depending on tire size and inflation limits.