How to Understand Numbers on Tires

The numbers on the side of a tire reveal important information.

Tires have several numbers stamped on the sidewall of the tire. Two of these are of primary importance to the consumer. These include the tire size and date of manufacturing. Tire size gives you the dimensions of your tire. Date of manufacturing tells you when the tire was made, which is important in determining how old a tire is and when it may no longer be reliable.

Instructions

Size

1. Locate the big, bold letters that looks something like 245/40R16 92V. These are the tire size, load rating and speed rating numbers, and they are usually located in the center of the sidewall, bigger than all the other print.

2. Look at the first number, 245 in the example. This number represents the width of the tire in millimeters.

3. Locate the second number, 40 in the example. This represents the aspect ratio, or the ratio of height to width, expressed as a percentage. In the example, the sidewall height would be 40 percent of the width of the tire. In this example, 40 percent of 245 millimeters equals 98 millimeters.

4. Look at the third number, 16 in the example. This represents the rim diameter in inches.

5. Find the final number and letter combination, 92 V in the example. The 92 represents the load rating. The example's 92 means the tire can support a maximum of 1,389 pounds. The "V" is the speed rating, which is 149 mph in this example. This represents the maximum speed the tire is rated to be able to sustain.

Date of Manufacture

1. Look for a label that starts with "DOT" followed by 10 to12 characters. This is usually located on the inner edge of the tire in medium-size print.

2. Locate the three- or four-number code at the end of that series. As an example, it might say 1007.

3. Read the first two digits of this code. This corresponds to the week of the year in which the tire was produced. The tire from the example was thus produced in the 10th week of the year, or the middle of March.

4. Look at the last digit(s). If there were only three digits in the code, then the tire was produced before 2000, and the single digit left is the year of some decade; no further information is presented to tell you which decade, though. If there were four digits in the code, then the last two digits represents the year. In the example, the tire was produced in 2007. It is generally recommended to replace any tire older than 10 years.

References

• Hemmings: Sidewall Markings
• Tire Rack: DOT Tire Identification Number
• Tire Rack: How to Read Speed Rating, Load Index & Service Descriptions