Jack Williams

How to Translate a Vehicle Tire Size

When you need new tires, the first question is often, "What size?". And though you may (or may not!) know the answer to that question, there is a good chance you have no idea what it means.

You know that the tiny print inside the sidewall mean something, but "what" is the question.

According to HowStuffWorks.com, this is what you should know:

Tire Type

The P designates that the tire is a passenger vehicle tire. Some other designations are LT for light truck, and T for temporary, or spare tires.

Tire Width

The 235 is the width of the tire in millimeters (mm), measured from sidewall to sidewall. Since this measure is affected by the width of the rim, the measurement is for the tire when it is on its intended rim size.

Aspect Ratio

This number tells you the height of the tire, from the bead to the top of the tread. This is described as a percentage of the tire width. In our example, the aspect ratio is 75, so the tire's height is 75 percent of its width, or 176.25 mm ( .75 x 235 = 176.25 mm, or 6.94 in). The smaller the aspect ratio, the wider the tire in relation to its height.

Tire Construction

The R designates that the tire was made using radial construction. This is the most common type of tire construction. Older tires were made using diagonal bias (D) or bias belted (B) construction. A separate note indicates how many plies make up the sidewall of the tire and the tread.

Rim Diameter

This number specifies, in inches, the wheel rim diameter for which the tire was designed.

The next time you answer the question, "235/75R15", you'll know exactly what you just said!