Tire size and rating: What do letters and numbers mean?

Your tires can’t talk, but they have a lot to say. Not all tires are made equally, and most of the details that make the difference between Bridgestone Blizzak and Pirelli P Zero are summarized in the sidewall. The meaning of the letters and numbers on your tires is here.

The most basic information you will find on the sidewall of a tire is related to its size. It is usually spelled 185 / 65R15, for example, although you will sometimes see “P” (for passenger cars) or “LT” (for light trucks) before this sequence. The first number corresponds to the width of the tire in millimeters; In this case, the tire is 185 mm wide. The second number indicates the ratio of the shape of the tire; It is expressed as a percentage. Using the same example, the height of this tire corresponds to 65% of its width. The ratio of the shape of high-profile tires is higher and vice versa: 2022 Jeep Wrangler Sahara 255 / 70R18 after tires while the front tires of Lamborghini Hurac├ín EVO 245 / 30ZR20 unit.

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It is followed by the letter R, which appears on almost every tire, regardless of the type of vehicle installed. It stands for “radial” and indicates that the radial layers make up the tire. The alternative is bias-ply, a type of construction that is becoming increasingly obsolete. Bias-ply tires are commonly found in older cars and their sizes are usually different from those of radial tires. Finally, the last number matches the size of the wheel that the tire can be mounted on. Again using the example shown above, this tire was made for 15 inch wheels.

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These are the basics, but there is a lot of other useful information written on the sidewall of standard tires. Each tire produced since 1979 must have a Uniform Tire Quality Grading (UTQG) mark that provides tradeware, traction and temperature ratings. Treadwear matches how long a tire lasts under normal driving conditions. The tradeware rating in our example is 400, which means it should last twice as long as a tire with a 200 rating, although how many miles you get out of it depends largely on how you drive.

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Traction rating indicates how a tire works on a wet surface; AA is the highest level, followed by A, B, and C. Lastly, the temperature rating tells you that the tire is able to compare with the heat it produces and corrodes. A rating corresponds to speeds above 115 mph; A tire with a B rating is good for 100 to 115 miles per hour; A C rating means the tire can handle speeds between 85 and 100 mph.

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Speaking of speed, there is another sign that tells you how fast your tires were designed to go. It is sometimes listed after size or dimension, although it may be somewhere else on the sidewall. Our example rating is 88T; T means the tire is safe up to 118 mph. At the bottom end of the chart, an R-rated tire is certified for 106 miles per hour. At the top end, a tire with a Z rating is safe even at speeds of up to 150 miles per hour. For numbers, in this case 88, it is the load rating; This indicates how many pounds each tire can carry. It is also scale-based: 70-rated tires can carry 739 pounds, while 126-rated tires are good for 3,748 pounds. In our case, 88 means 1,235 pounds.

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One of the things a tire can give you is its age. Instead of asking for its ID, look for a four-digit code that is often (but not always) located in an oval shape. In the image above it is “4117”; This means that our tires were made in the 41st week of 2017 This information is effective because there are two main reasons to replace a tire: when it is worn and when it is old. Tires have an expiration date, this is usually about six years and need to be replaced when they arrive even though they have zero miles.

Some of the other symbols are miscellaneous code. You may see a batch number that means little to the average driver, unless the manufacturer issues a revocation, for example. And, instructions are often written on the sidewall to tell mechanics which way the tire should be mounted, or which way the tire should be facing and which way it should be facing. Weight and air pressure ratings are also usually on the sidewall.

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