The internal construction of a tire is indicated by a single letter following the tire's aspect ratio. This letter reflects the construction of the tire body plies. ('Plies', or 'ply cords' are the layers of fabric that make up the body of the tire). There are three generally types of construction:

R - Radial (the most common type in passenger cars built after 1980)
D – Diagonal
B – Bias

In the example below, the "R" indicates the tire is of radial construction.

Example Tire Size: P 215/60/R16 94V

To determine the right tire size and specications for your vehicle, the best resource is your vehicle owner's manual or the sidewall of your existing tire. The sidewall will provide the exact sizing information from the tire manufacturer.