And the 15 is the size of the wheel it's designed for. So, in this case you've got a 31-inch tall tire for a 15-inch wheel. You know the wheel radius is 7.5-inches, and the tire radius is 15.5 inches.

— The Tire Industry Association (TIA) has published OTR tire and wheel weight charts covering more than 150 earthmover and industrial/forklift tires and tire/wheel assemblies. These comprehensive ...

If you look at the side of your vehicle's tires, you'll notice a line of numbers. One of these number sets is the tire load index. Here's what that means.