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What Do The Numbers On A Car Tire Mean

They’re probably the most thought about car part: Tires. Without them you can’t get down the road and, although there are many sizes, nowadays there is one most popular kind. Here’s a guide to what you need to know if you need new treads or are just trying to stay inflated on your drive. 

What Do The Numbers On A Car Tire Mean?

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Tire Size Numbers Auto Repair

Pressure, load rating, diameter, width; all these things can be identified with just a glance at your car’s tires. So how can you achieve this auto-savvy skill? It’s simple, here’s a breakdown of where to find all this information on the sidewall of your tire.

Maximum Tire Inflation Pressure

This number is probably the most mistaken. Unless you have a flat or are in the market for new tires, you’ll probably only check the side of your tires to find out how much air to put in them. Ironically, this is one of the biggest mistakes! This is the absolute maximum amount of air that the tire can hold and it is best not to fill them this far. To find the ideal running pressure check inside your car's door jamb. Each car manufacturer has calculated a specific pressure based on the individual vehicle model. Be sure to keep in mind the pressure is specified for a cold tire. 

Car Tire Size Numbers

If you’re looking to purchase new tires to fit your car, you’ll be interested in the string of numbers and letters that indicate the size of your tire.

The beginning of the string is the tire Type. Most commonly you will find ‘P’ for a P-metric passenger car tire. Also, your tire may indicate "LT" for a Light Truck Tire or no letters for a Euro Metric tire.

Next is a three-digit number of the tire’s Width. For instance, in the pictured tire size 225/70 R15, the width is 225 Millimeters.

The width is followed by a slash and a ratio for the Aspect Ratio of the tire. In our example of 225/70 R15 the aspect ratio shows that the height of the sidewall is 70% of the tire width. The higher this number is the larger the sidewall will be. 

After the size and width is the Construction of the tire. The letter ‘R’ means ‘Radial’. This tells that the rubber of the tire is patterned radially or at an angle to the center of the tire. Radials are the most common kind of tire available today.

The next number is the Diameter of the tire. This is a measure in inches of the wheel that the tire sits on. Our example of 225/70 R15 is a tire for a 15" wheel diameter. 

What Is The Load Rating Of A Tire?

Following the size will be a two to three-digit number showing the tire Load Index. The tire load index is a representation of the amount of weight that an inflated tire can support. It is important to choose a tire with the proper load index for your application. See a full tire load index chart on our Tire Services page.

What Is A Tire's Speed Rating?

The final piece of the puzzle is a letter indicating the Speed Rating of your tire. This is the maximum speed that a tire is designed to handle. Again, very important to match your tire to the proper application. A speed rating chart is also located on our Tire Services page.

Need help with your tires? Call Frank’s at (215) 355-8877!

Tire Maximum Inflation

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