determining pay load capacity

Also note that tires used on a dually axle, must have the tires sidewall rating REDUCED

Have to check the tire OEM’s spec page for your tire. The tires that came with your dually already has the debating by the OEM, but if your are going to re-engineer by changing sizes/class/etc...you need to know this

Tirerack tires debated in a dually app

Snip...

Light truck tires that are intended to be used in dual applications have two "Max Load" ratings branded on the tire's sidewall. This is because the load capacity rating of a tire serving duty in a "single" application is greater than the exact same tire being used in a "dual" application. For example, a LT235/85R16 Load Range E tire is rated to carry 3,042 pounds when inflated to 80 psi and used in a single application, but only 2,778 pounds when used in a dual tire application at the same inflation pressure.

This reduction in rated load capacity results in slightly larger tires being specified for the application that can better withstand the additional stresses experienced when a single tire goes flat and the three properly inflated remaining tires are required to temporarily carry the load at reduced speeds to remove the vehicle from immediate danger. This load reduction is not a concern for vehicles originally equipped with dual rear tires because the vehicle manufacturer factored it in when they specified the tire size for the vehicle.