To begin, locate the abbreviation "DOT" on the tire’s sidewall. Nearby, you will find the DOT code, which typically spans 10 to 13 characters. These characters, a mix of letters and digits, each hold specific meanings. Note that while the digits range from 1 to 0, certain letters—G, I, O, Q, S, and Z—are omitted to avoid confusion due to their resemblance to numbers.

DOT Code Example

If you encounter a DOT code shorter than 10 digits, it may be that you are viewing only a part of it, excluding the date code. This is usually the case on one side of the tire—the side that is not intended to be outward-facing. Therefore, inspect the opposite side to find the complete DOT code, including the date code. 

Navigating Manufacturer Codes in DOT Numbers

The initial two or three digits of a DOT code represent the manufacturing plant. Historically, up until April 2015, all plant codes consisted of two digits. Post-April 2015, the inclusion of a third digit became permissible, and by April 2025, three-digit codes will be mandatory. During this transition period, both two-digit and three-digit plant codes will coexist.

To facilitate this change, the National Highway Traffic Safety Administration (NHTSA) has introduced a series of three-digit codes. These new codes begin with the number "1," followed by the original two-digit codes. While adopting this new coding system isn't mandatory, it is anticipated that most manufacturers will implement it.

Thus, from April 2015 to April 2025, you may encounter plant codes that begin with "1" but otherwise remain consistent with the historical coding system.

For example, if you encounter a plant code like "0C" within a DOT number, this identifies a specific manufacturer and location, which, according to previous records, corresponds to Michelin in Chonburi, Thailand.

Manufacturer Code

For more accurate and updated information on plant codes, the following resources can be consulted:

• Archived Records: Past records of plant codes can be accessed via the Wayback Machine, which archives web pages.
• Legal Resources: Some law firms, like the Wetherington Law Firm, provide information on DOT codes. However, their focus on litigation against tire manufacturers may influence the content, so caution is advised.
• Dedicated Lookup Services: Websites such as NYSTire offer a lookup service for DOT codes, which can be more current than static listings.

Always verify the information from multiple sources when decoding DOT numbers to ensure accuracy and reliability.

Deciphering Tire Size Codes in DOT Numbers

Following the manufacturer's plant code, the next two digits within a DOT number signify the tire size. However, the interpretation of these size codes isn't standardized by the National Highway Traffic Safety Administration (NHTSA). Each tire manufacturer is allowed the flexibility to assign these codes as they see fit, provided they maintain a consistent and explainable system within their coding.

To aid in standardization, the Rubber Manufacturers Association (RMA), an industry group representing U.S. rubber manufacturers—including major tire producers—has issued a suggested list of size codes. This list is detailed in the RMA Size Code Manual. It's important to recognize, however, that updates to this manual occur periodically, and not all information may be current. Additionally, adherence to the RMA's coding system isn't universal. Many European tire manufacturers, for instance, opt for different coding systems.

The DOT size codes are applicable to various types of tires, and the RMA provides separate lists for each category, including passenger, truck, and motorcycle tires.

For instance, consider a DOT code where the plant code is "OC," which identifies the Michelin factory in Chonburi, Thailand. Following this, the size code "WC" might correspond to the tire size 205/55 R16 —although, due to the non-prescriptive nature of these codes, "WC" could potentially represent a different size based on the manufacturer’s internal system.

Tire Size Code

For the most accurate interpretation of tire size codes, it may be necessary to consult the manufacturer’s own resources or the RMA Size Code Manual, keeping in mind that updates may have occurred since the last publication.

Understanding Tire Type Codes in DOT Numbers

After the size code, the next sequence in a DOT number consists of three or four digits that designate the tire type. This coding, though optional, is widely used by tire manufacturers for internal tracking purposes, such as managing returns and quality control. The decision on how exactly to code the tire type lies with each manufacturer, leading to a variety of coding systems across the industry.

Although the coding system is not standardized, it's unusual to find a manufacturer that doesn't utilize it, given its utility in logistics and inventory management.

Tire Type Code

For example, the type code "03XX" helps to specifically identify the tire model. While "X" is commonly seen in Michelin tire codes, it's important to note that Michelin is not the only manufacturer that might use "X" in their type codes.

The presence of "X" in a Michelin type code does not exclusively belong to Michelin, as other manufacturers may also use an "X" in their system for different purposes or tire characteristics. This exemplifies the diversity in coding practices among tire manufacturers and underscores the importance of referencing specific manufacturer guidelines or databases to accurately interpret these codes.

Decoding the Date Code on Tires

The date code is the final component of the DOT number, important for identifying when the tire was manufactured. This code always consists of numbers and follows a specific format to represent the manufacturing date: week/week/year/year or week/week/year. Since the year 2000, a four-digit system has been standard. However, during the transition years of 1999 and 2000, both three-digit and four-digit codes were used. For example, 032 signifies that the tire was manufactured in the third week of a year ending in "2" – this could be 1992, 1982, or 1972, but not 2002 due to the three-digit format.

Date Code

Regulatory Notes and Manufacturing Challenges

It's important to note that the date code is only required on one side of the tire. While the rest of the DOT code may appear on both sides, the date code often appears solely on the side intended to face outward. Since 2008, regulations have stipulated that the full DOT code, including the date code, should be on the side intended to be outward. For tires featuring a white sidewall or white letters, this would typically be the white side.

However, this requirement has posed challenges for manufacturers, particularly because the date code part of the mold is usually on the top half. Changing this plate weekly necessitates someone working in the hot, lower half of the mold—a risky and dirty task that has led some manufacturers to petition the National Highway Traffic Safety Administration (NHTSA) for a change in this requirement. The outcome of this petition remains uncertain.

FAQs

Most frequently asked questions about tire DOT Codes:

• Q: How Can the DOT Code Help in Identifying Recalled Tires?
  A: In case of a tire recall, manufacturers and safety authorities use the DOT code to identify affected tires. The DOT code allows consumers to check if their tires are part of a recall by matching the code with the recall notice. This helps ensure that potentially dangerous tires are removed from service promptly.
• Q: Can I Use the DOT Code to Verify the Authenticity of My Tires?
  A: Yes, the DOT code can help verify the authenticity of your tires. Counterfeit or substandard tires often lack a proper DOT code or have a fake one. Checking the code against official records can help ensure you’re using genuine, compliant tires.
• Q: What Should I Do If My Tires Don't Have a Visible DOT Code?
  A: If your tires lack a visible DOT code, it could indicate they are not compliant with U.S. regulations, which is a red flag for safety. Such tires might be gray market imports or illegal copies. It’s advisable to replace them with DOT-compliant tires to ensure your safety and legal compliance.
• Q: Can the DOT Code Influence Your Tire Warranty?
  A: Yes, the DOT code can affect your tire’s warranty. The manufacturing date within the DOT code is often used to determine the start of the warranty period. Knowing how to read this code ensures you’re aware of how long your tire is covered and can help you make warranty claims more effectively.
• Q: What Hidden Information Can Be Discovered by Analyzing the Plant Code in the DOT Code?
  A: The plant code within the DOT code can uncover hidden details about where and how your tire was made. Some plants are known for their state-of-the-art technology and high standards, while others might have had historical issues. Understanding this can give you insights into the potential quality and reliability of your tire.