View Here : Deciphering Tire Sizes
For example, size 7.50R16LT/D refers to a radial light truck (LT) tire with a cross section width of 7.5 inches and a load range of D. Tires identified as "ST" are "special trailer" tires, designed to only be used on trailers such as boat, car or utility trailers. They should never be used on passenger cars, vans, light trucks or SUVs.
This tutorial will help give you a better understanding of how to read the numbers, and how they will affect your ride. 1.) The first MUST with understanding how tire sizes/specs work is a breakdown of the individual numbers within the size set. (Will be using metric measurements for this tutorial) Lets use 225/45R17 as an example.