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Which Tire Size Do I Need to Buy?

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Sometimes, you know immediately when it's time to get new tires. One could blow out while you're driving, or you might begin to feel an immense vibration every time you get behind the wheel. Other times, the wear and tear happens over a long period. Your once-new tires become threadbare, underinflated or cracked the more you use them, and you begin to think it's time to shop around for a new set. Understanding exactly which tire size to buy is a critical first step in ensuring you stay safe on the road. Here's a quick guide to get you started in understanding tire sizes.

Locating Your Tire's Sidewall

Take a look at the side of your tire. Do you see that code of numbers and letters? It's usually located beneath the the name of the tire manufacturer. Chances are, you've looked at it quite often but never knew what it meant. A car tire size chart can tell you similar information, but before you go digging for your owner's manual, start here first. That string of characters is actually full of information about your tire type, size, construction and more. Jot it down completely before moving forward.

Knowing Your Tire Type

Does the code on your tire sidewall begin with "P?" Most do. This tells you that you have passenger-type tires that conform to specific standards, known as P-Metrics, mandated across the United States. If your code begins with the letters "LT," that simply means that those tires are made for light truck use. Though some trucks are equipped with P-Metric tires, certain manufacturers equip their vehicles with LT tires instead. They'll operate the same way but may require more inflation under higher pressure than their P-Metric counterparts. If your code doesn't have a "P" at the beginning, it conforms to Euro metrics instead. While they may look and operate similarly, it's important to understand that P-Metric and E-Metric tires have different load limits. You'll need this information when you're looking for the ideal tire size for your vehicle. You can use it to compare your tires on a tire wheel size chart moving forward.

Determining Your Tire Width

To measure the width of your tires, simply look at the number after the first letter of your code. This is the measurement from one sidewall of your tire to the next. This is a three-digit number measured in millimeters. So, if yours says 215, that means that the tire is 215 millimeters in width.

Finding the Aspect Ratio

The next dimension you'll need is the aspect ratio. After your tire's width, you'll see a slash in the code. The next two digits that follow describe this ratio. The aspect ratio is comprised of the height of your tire from its cross-section measured against its width. So, if your sidewall code says 215/65, that means the height measures 65 percent of its width of 215 millimeters. An alternative is to search a tire height chart by size to find your measurement.

Understanding Tire Construction

Next, take a look at the letter that follows the aspect ratio dimension. If yours says "R," that means you have radial tires. This simply means the layers in the tire are arranged radially across it. The most common alternative is bias ply, which is a tire construction that's more common for older vehicles.

Calculating Tire Diameter

Finally, you'll need to know the size of the wheel that your specific tires should fit. You can find this by measuring the tire's diameter. While you could look yours up on a tire diameter size chart, you can also find your answer by searching the tire sidewall. Following the letter that indicates your tire construction, you'll find the diameter listed in inches as the next two digits. For instance, your code might read 215/65 R12, meaning the diameter is 12 inches. With this information in hand, you can visit your local tire supply store armed with the knowledge you need to find the exact tires that are designed to fit your vehicle, look great and give you peace of mind on the road.

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