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By Tire Agent Staff
December 31, 2021
Tires are dotted with letters and numbers that seem like an alphabet soup of codes. Although they're intended to pass along information to consumers, you need to be a code cracker to understand the DOT number meaning.
In a related post that about DOT numbers on tires, we explained how to find tire sizes, load indexes, speed ratings, and age on a tire's sidewall. In this post, we'll break down the DOT tire identification number and what they mean.
The DOT stands for Department of Transportation, which the U.S. congress established in the 1960s to over see public transportation. The DOT oversees 11 agencies that set guidelines for passenger vehicles, trucking, railroads, airways, maritime and other transportation. It's the National Highway Traffic Safety Administration (NHTSA) that sets standards for tires that are sold to American consumers, both for passenger and commercial vehicles and equipment.
Why do you need to know what your DOT codes mean? The information lets you know if the tires are right for your vehicle, driving style, and road conditions, plus they tell you how old tires are.
Look for the DOT letters on the tire and note the string of letters and numbers that follow the "DOT." These are the numbers you should care most about: plant code and manufacturing date.
By the way, some people erroneously refer to the DOT sidewall number as a tire's serial number. This would imply that each tire has its own unique code. Some manufacturers may choose to serially number their tires, but that is not the DOT number. The DOT number indicates the manufacturing date and location of a tire.
The first 2 or 3 letters or numbers refer to where the tire was made. In the photo above, you can see a 4U, which refers to a Yokohama Tire Company manufacturing plant that's located in the Philippines. How do we know the location?
Although tire makers are required to disclose the plant number, that doesn't make it easy to interpret the code. To find out where a tire was made, use the DOT tire code lookup:
1. Locate the manufacturing plant number on your tire. It's the first two or three digits after the DOT letters.
2. Open the NHTSA vPIC database.
3. Locate the vPIC MID (Manufacturer Information Database) and set Equipment Type to Tires and DOT Code to those first two or three digits from your tire (in this example, it's 4U). Make sure only the "Equipment Plants" box is checked; uncheck Part 565, Part 566 and Part 586 to look up a plant number.
Tap the search button. If you entered the information correctly, the NHTSA database will give you the name of the manufacturer, the city, state/province, postal code, and country of the manufacturer. In this example, it's Yokohama, Clark Field, Pampanga, 2023 Philippines.
The last four numbers of the DOT marking on tires tell you the week (1 through 52) and year the tire was made. So, a tire with the last four digits of 0121 was made the first week of January 2021, 0221 is second week of January of 2021, and so on.
If you'd prefer to skip the figuring, you can use this handy website, CheckTire. Not only will it tell you when the tire was made, it will also tell you how old the tire is and whether it's time to replace them based on their age.
Vehicles typically have a shelf life of 5 to 6 years, but some can last up to 10 years. Tires older than that are subject to dry rot, which is when the sidewalls and treads of tires crack because the rubber dries out. Dry rot is dangerous and could cause your tires to blow.
Older tires are dangerous, and while we know you want to get every mile out of your tires, we also want you to be safe. This guide explains how often you should replace your tires and how to know when it's time to replace them.
To geek out over more DOT tire regulations, visit the NHTSA's tire safety information site for consumers. You can also download the DOT's SaferCar app for iOS and Android to sign up for vehicle safety and recall alerts.