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How to Read Tire Size

How to Read Tire SizeIf you need to replace a tire near Harrisburg, Mechanicsburg, or Trevose, it’s crucial to get one that matches the others. You can do this by matching the size, which is found on the tire sidewall.

We’ll tell you exactly how to read tire size, and what the various letters and numbers mean. That way, you can understand why a specific tire is being outfitted on your automobile.

Read through the information below, and contact Faulkner Auto Group if you have any questions.

Deciphering a Tire Sidewall

Tire Measurement When you look on the side of a tire, you’ll find a variety of letters and numbers. These indicate things like tire size and type. Plus, you’ll find markings that indicate the tire meets safety requirements determined by the U.S. Department of Transportation (DOT).

To explain what the letters and numbers on a tire sidewall mean, we’ll use the example “P225/45R17 91V.”

Tire Type

The first letter, P, refers to tire type. This tells you that the tire is intended for passenger vehicles. In some instances, you may see LT, which indicates that the tire is used for light trucks.

Tire Width

Right after P is 225, which represents the tire width. It’s measured in millimeters and is the width of the tire from sidewall to sidewall. So, in this case, the tire would be 225 millimeters in width.

Aspect Ratio

How to Read Tire SizeThe number after the slash, 45, represents the aspect ratio. This is the ratio of the sidewall’s height to its width, represented as a percentage. In this example, the height would be 45% of the 225-millimeter width, which would equal 101.25.


After 45, you’ll see the letter R, which stands for Radial. This means that layers of fabric run radially across a tire, and it has additional layers around the circumference. Almost all tires sold today are radial.

However, you may find some tires with the letter D on them, which stands for Diagonal Bias construction. This is mainly on truck tires, and it means that the internal body layers of a tire run crisscross in a diagonal pattern.

Wheel Diameter

After R comes 17, which is the Wheel Diameter. This is the size of the wheel measured from one end to another. Essentially, it tells you the size of the wheel that a tire is intended to fit. In this instance, the tire is made for a wheel with a 17-inch diameter.

Load Index

Next comes the Load Index, which in the above example is represented by 91. This indicates the maximum load carrying capacity of a tire. Different numbers represent different weights, based on what model you have.

In this case, 91 means that it can support 1,356 pounds at maximum air pressure. Multiply that by four tires, and your vehicle’s maximum load carrying capacity is 5,424 pounds.

Speed Rating

The last digit on the tire (in this case, V) represents the Speed Rating. Speed ratings are represented in letters ranging from A to Z and designate the maximum speed that properly inflated tires can be driven on. For this tire, the maximum speed rating is 149 MPH.

Learn More at Our Tire Center

If you need more information about tire size, then contact Faulkner Auto Group. We can also perform any tire repairs or replacements needed near Harrisburg, Mechanicsburg, or Trevose.

Don’t wait. Contact us today!