F 250 Tire load rating.

Load rating has to do more with the sidewall profile and width than it does wheel diameter. With smaller diameter wheels, you can get a higher profile tire in the wheel well - that's all. As a general rule, you will LOOSE load capacity as you increase the wheel diameter because you have to use a lower profile tire to keep the outside diameter the same. Also, different manufacturers may have a slightly different rating for the same size tire in the same load range. Here's a good place to look at different options and then see what tires are available in the size you choose:

Tire size calculator

Note that, as you change wheel sizes and tire profiles, the outside diameter of the tire will change, causing changes in final gear ratios and height of the vehicle - very important when towing.

Rob