What are some good resources that explain how to read a tire size chart?

Although they do not provide tire charts per se, Goodyear and Tire Rack both provide instructional material on finding tire size. Most of the information is found by reading size information located on a tire's sidewall. Here one can find tire width, type, aspect ratio and wheel diameter.

A tire sidewall often identifies tire type, with P standing for "passenger" and LT representing "light truck." Tire width is the measurement between the edges of both side walls, whereas the aspect ratio measures the relationship of the tire's width to the height of its cross-section. Wheel diameter helps to determine proper tire size.