How to Read a Tire Sidewall

One neat element of tires is that they each have specific identification details etched into the sidewall that read when, where, and how the tire was made.

In 1971, the US Department of Transportation (DOT) passed a requirement that all tire manufacturers include a Tire Identification Number (TIN) on each product. They established the TIN as a guaranteed method for notifying consumers of tire recalls. Each tire has a TIN imprinted on one of its sidewalls where retailers and consumers can easily locate important information.

Learning how to read a tire sidewall is a useful skill to have whether you are purchasing new tires, considering replacing your current tires, or deciding if you should use an old set of tires.

Once you gain this skill, you will be able to track your tires’ origin down to the week they were produced. Plus, you will know the specifications and capabilities of the tire itself.

Tire Identification Number (TIN)

The tire identification number tells you exactly who manufactured your tires and when/where they did so. Here is an example of a TIN:

DOT 4B08 4DHR 2910

The TIN always begins with “DOT” and is followed by the manufacturer code and tire size. In this case, “4B” refers to a specific tire plant, while “08” is the manufacturer’s tire size.

Each manufacturer puts model-specific information in the third grouping of characters. This information is not readily available to consumers.

The last four numbers in the TIN are the most important—at least as far as consumers are concerned.

DOT 4B08 4DHR 2910

In this case, the tire was manufactured in the 29th week of 2010. This is valuable information when you are considering a replacement of your tires. If the tires are more than six years old, you should change them regardless of the tread depth.

Tire Size

The first number in the tire code designates the section width, or the distance (in millimeters) from sidewall to sidewall. It includes three digits. Consider this example:

180/55ZR17

From this information we now know that the tires have a width of 180mm. Next to the tire width you will see the aspect ratio, which in this case is 55.

180/55ZR17

The aspect ratio compares the height of the sidewall to the overall tire width. In other words, an aspect ratio of 55 simply means that the sidewall height is 55% of the total width (180mm).

Following the aspect ratio, you will find information on the tire’s construction:

180/55ZR15

R: Radial construction – Body plies are laid parallel to one another and perpendicularly to the bead

B: Bias-belted construction – Body plies are overlapped diagonally and sit at an angle to the bead

The very last piece of information in the sidewall code tells you the wheel’s diameter.

180/55R17

In this case, the tire will fit a 17-inch wheel. Understanding how to read this information is important when purchasing tires. When you contact different tire vendors for quotes, you will need to provide them with the tire specifications.

Speed Rating and Load Index

The tire size information is proceeded by its speed rating and load index classification:

180/55ZR17 (73W)

The number 73 refers to the tire’s load index classification, meaning that the tire can hold up to 805 pounds. The higher the load index, the more weight the tire can withstand. You can find the corresponding weight and load indices on a standardized chart.

In the above example, the letter “W” is the tire’s speed rating. These ratings range from A to Z, and they represent the maximum speed a tire can handle based on its tolerable load capacity.

A tire with a speed rating of W can withstand a speed of up to 168 miles per hour. This information gives you a guideline for using your vehicle to haul large loads. If you exceed the load capacity or speed rating recommendations, you could risk damaging your vehicle beyond repair.

Using Tire Sidewall Information

Given each tire’s unique set of sidewall inscriptions, you can learn a great deal about its origins and capabilities. Sometimes tires also have special markings such as snowflakes and mountains to illustrate their ability to work through inclement weather.

Understanding your tire’s load capacity constraints, speed ratings, and age will help you to take better care of your entire vehicle. As a powerful foundation for all the driving you do, tires are an important purchase to make. With the information in this guide, you will know when to replace them and how much weight and speed they can handle.

If the info you read on your tire sidewall indicates your tires are from more than five years ago, it is wise to replace them as soon as possible. Contact Dunlop Motorcycle Tires today to get started on an order.