DOT – three letters found on every tire, yet often remain a mystery. What’s hidden behind this cryptic combination of letters and numbers? Simply put: DOT stands for “Department of Transportation” – the U.S. Department of Transportation. But that’s just the tip of the iceberg. The DOT marking is part of a complex code that reveals important information about the tire, from its manufacturing date to its performance characteristics.
Let’s say you’re standing in front of a stack of tires in your workshop. A customer needs new summer tires and trusts your expertise. Wouldn’t it be embarrassing if you couldn’t tell them when a specific tire was produced, right? This is exactly where the DOT marking comes into play.
Decoding the DOT Number
The DOT number is a sequence of letters and numbers that tells you when and where a tire was manufactured. You’ll find it on the tire sidewall, usually near the ‘DOT’ inscription. The first two letters indicate the plant where the tire was produced. The next two represent the tire type and size.
The last four digits are particularly important: They indicate the manufacturing week and year. Let’s take the digit sequence “1223” as an example. The first two digits (“12”) indicate the twelfth week of the year, and the last two (“23”) indicate the year 2023. So, a tire with this DOT number was manufactured in the twelfth week of 2023.
Why is the DOT Date So Important?
The ‘why’ is simple: A tire’s quality decreases over time, even if it’s not used. Similar to food, tires also have an “expiration date.” According to experts, tires – even unused ones – should be replaced after about six years. Because over time, the rubber can become porous, negatively impacting driving characteristics.
“An old tire might look good at first glance,” says Dr.-Ing. Markus Schmidt, a tire expert at the Technical University of Munich. “But the internal structures change over time. This can lead to an increased risk of tire blowouts and accidents.”
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DOT Marking: More Than Just the Manufacturing Date
However, the DOT marking also includes other information that can be relevant to you as an automotive professional:
- ECE Mark: This mark confirms that the tire complies with European safety standards. It consists of a circle with the letter combination “ECE” and a number indicating the approval country.
- Load Index: This number indicates the maximum weight the tire can carry. You’ll find it next to the tire size.
- Speed Rating: This letter indicates the maximum speed for which the tire is designed.
Common Questions About the DOT Marking
What do the letters after the DOT number mean? These letters indicate the tire type and size.
How old can a tire be at most? Experts recommend replacing tires after no more than six years, even if they haven’t been used.
Where can I find the DOT number on the tire? The DOT number is located on the tire sidewall, usually near the ‘DOT’ inscription.
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The DOT Marking: Your Key to Tire Safety
The DOT marking might seem confusing at first glance, but it provides valuable information about a tire’s safety and performance. With this knowledge, you can best advise your customers and ensure they travel safely and comfortably.
Image comparing a healthy new tire to a degraded old tire
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