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The Hood Magazine

How to Read Tire Sizes on a Tire Sidewall

02/28/2019 03:41PM ● By Digital Media Director

By: Discount Tire

Here are some tips for reading your tire sidewall from your neighborhood experts at Discount Tire:

P-Metric Sidewall Code (Tire Class)

The first letter represents the tire class. If a tire has a “P” at the beginning of the sidewall code it tells us the tire is P-Metric, which refers to tires made to certain standards within the United States. An “LT” at the beginning means that it is a Light Truck tire, and a tire with no letters indicates a Euro-metric tire.

Section Width

The three digits that immediately follow the tire class letter represent the section width in millimeters. This measurement refers to the distance between the furthest points on the tire’s two sidewalls. The larger the measurement, the wider the tire is.

Aspect Ratio

After the section width, you’ll find a forward slash and a two-digit number. That number is the aspect ratio, which expresses the tire sidewall height as a percentage of the width. For example, a tire with an aspect ratio of 65 has a sidewall height of 65-percent of the width.

Tire Construction

The letter following the aspect ratio indicates the tire construction type. The letter may be either “R” for radial tire or “D” for diagonal bias tire. Radial tires are the most common tire type on the market today.

Wheel Diameter

The final number represents the wheel diameter. This refers to the wheel size that the tire is engineered to fit. If the wheel diameter on a tire is 16, it can only be mounted on a 16-inch wheel.

You can find the recommended tire size on your vehicle’s tire placard (usually located on the driver’s door jamb) or in your owner’s manual.