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Despite being the only point of contact between a car and the road, tires are a bit of a mystery for some drivers when it comes to understanding the different numbers, letters, and symbols on their side. If you find yourself among this company of motorists, you're far from a small group. Many drivers are happy to have a tire shop replace the tires when the tread gets low, either asking for the same tire that is already installed on the vehicle or taking the recommendation of the tire service staff for a different tire if that particular model isn't available. 

If you're looking to improve your automotive and tire knowledge, however, you're at the right place!

At Bobby & Steve's Auto World, we love when customers are interested in learning more about their vehicles and the many parts that keep it moving, such as the tires! Those of us in the tire and automotive service business have an appreciation for everything that goes into the design and performance of a vehicle, so we understand your drive for knowledge.

So with that said, let's take a closer look at your tires.

Understanding the Tire Sidewall

The markings on a tire's sidewall tell you the following:

Tire Type: The first letter indicates the type of tire. For example, "P" stands for passenger vehicle tire, while "LT" means light truck tire. Others you may see include "T" for temporary spare (think donut tires), AT for all-terrain tires, MT for mud-terrain tires, and "Z" for high performance tires. There are others letters for reinforced tires, run-flat tires, and specific designations of performance tires.

Tire Width: The three-digit number after the tire type indicates the tire's width in millimeters from sidewall to sidewall. For example, "225" means the tire is 225 millimeters wide.

Aspect Ratio: Following the slash after the tire width, the two-digit number represents the aspect ratio, which is the height of the tire's sidewall expressed as a percentage of the tire's width. For example, "55" indicates that the tire's height is 55% of its width.

Construction: Another letter follows the aspect ratio, indicating the tire's construction. "R" stands for radial, which means the layers run radially across the tire. "D" would indicate diagonal or bias ply construction.

Wheel Diameter: The next number is the size of the wheel that the tire is intended to fit, measured in inches. For example, "16" means the tire is designed to fit a 16-inch wheel.

Load Index: This number corresponds to the maximum weight the tire can support when properly inflated. You'll need a load index chart to translate this number into actual weight.

Speed Rating: The letter at the end, often after the load index, indicates the maximum speed at which the tire can safely carry a load corresponding to its load index. Common speed ratings include "T" (118 mph), "H" (130 mph), and "V" (149 mph).

DOT Compliance: Tires sold in the USA will have the letters "DOT," which means the tire complies with all applicable safety standards established by the U.S. Department of Transportation.

Manufacturing Date: The last four digits of the DOT code represent the week and year the tire was made. For example, "1219" would indicate the tire was manufactured in the 12th week of 2019.

Other Markings: Tires may also have additional symbols indicating special features or approvals, such as "M+S" for mud and snow, or a snowflake symbol indicating the tire is suitable for severe snow conditions.

As you can see, a tire's sidewall provides quite a bit of information. While it's easy to get by in today's world without learning to to read your tires, it's still a neat to know how to do it. At Bobby & Steve's Auto World locations in Minnesota, we are happy to assist you with your tire buying journey, from start to finish. Our website also lets you shop for tires online by vehicle make and model, tire size, or VIN. We encourage you to give the tire size option a try with your new knowledge.

And don't forget—tire sidewall knowledge makes for great trivia night questions, as well!