Just a note: no modern tire actually has 8 plies. That's an outdated system of load rating, in which the capacity of the tire is related to the number of reinforcing plies a tire from half a century ago might have to get the same capacity.
Roughly, for small sizes such as those used for trailer tires and some light trucks...
- Load Range A = 2-ply rating (typically 24 psi max inflation pressure, no longer used)
- Load Range B = 4-ply rating (typically 35 psi max inflation pressure, normal for passenger cars)
- Load Range C = 6-ply rating (typically 50 psi max inflation pressure, very common for light trailers)
- Load Range D = 8-ply rating (typically 65 psi max inflation pressure)
- Load Range E = 10-ply rating (typically 80 psi max inflation pressure)
... and so on
In modern tires, the Load Range designation is still used but only in ST (Special Trailer), LT (Light Truck), and commercial truck/trailer types. In other types, and even in some LT tires, the terms Standard Load (SL) and Extra Load (XL) are used. An Extra Load tire on the tug would allow you to use more pressure which makes the tire stiffer, and even with the same pressure it might have stiffer sidewalls.
All tires currently offered by Nissan on the Frontier (at least in the Canadian brochure) are "P"-type (generally for passenger cars). None of these tires would have a "2-ply rating", but they might actually have two sidewall plies. An LT (Light Truck) or commercial tire even in the same size and with the same number of plies would likely be stiffer, without resorting to an extreme load range which would likely ride and handle poorly. Even the stiffest/highest capacity tire to fit the Frontier would not have 8 actual plies, but you could find an "8-ply rating" (or Load Range D) tire.
To really get stiff sidewalls for control, the effective methods are to choose
- short sidewalls (so low-profile tires, such as the P265/60R18 available from Nissan on the Frontier), and/or
- high performance tires
Again, actual ply count is not the issue. The 225/80R22.5 Michelin XRV
tires on my motorhome are Load Range G
, and have only a single-ply sidewall (although the steel cord of that one reinforcing ply is very thick).
For the 5.0 tug, I would look at lower-profile tires, or LT or commercial tires no more than one load range more than needed for the load. I would certainly use more air pressure in them when towing than when unloaded... I do that with my van and regular trailer.