Understanding How to Read Tire Sizes

Confusion might arise about tire size. On the sidewall, some of the numbers are listed in millimetres, while others are listed in inches. Additionally, depending on where you drive and how you drive your car, truck, or trailer may need a different size. You can find the size of the original equipment tires in your vehicle’s owner’s manual or on a sticker that is typically found on the driver’s side door jam. This is the size that the car’s manufacturer recommends. It’s simple to comprehend what all the letters and numbers on the sidewall of your tire signify with a little explanation. The numbers serve as benchmarks for tire performance, kind, and size. Well, in this article, you’ll be learning how to read tire size. We’ll also be discussing the different types of tire sizes.

How to read tire size

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Alright, let’s get down to it!


How to Read Tire Size

Understanding how to read tire sizes

When learning to read tire size, these are the major things you must understand:

  • Tire Type
  • Tire Width
  • Aspect Ratio
  • Construction
  • Wheel Diameter

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Tire Type

Tire Type

The “P” at the start of the “Tire Size” designates the tire as a P-Metric tire, which is a type of tire designed for passenger automobiles and manufactured in the United States to certain specifications. A tire is said to be Euro metric if its tire size begins with no letters. The load capabilities of P-Metric and Euro-Metric tires may differ.

The letters “LT,” either at the start or the end of the tire size, denote that the tire is designed for light trucks. Some light vehicles come from the factory with “LT” type tires. In comparison to passenger tires, these tires often need greater inflation pressures. For information on the recommended tire size and inflation pressure for your vehicle, consult your owner’s manual or tire placard.

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Tire Width

Tire Width

The width of the appropriate tires for your vehicle, in millimetres, is the first number to appear in your tire size information. The tire width is indicated by the first three digits of the tire size. For instance, the width of a tire with the size P215/65 R15 is 215 millimetres. The measurement from one sidewall to the other is always used to define tire width. Therefore, a tire marked “P215” is for a passenger car and has a nominal width of 215 millimetres.

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Aspect Ratio

Aspect Ratio

The next two-digit number you see after the slash represents the aspect ratio of the tire, which effectively indicates how tall the profile of your tire is: P215/65 R15. Delivered aspect ratios are expressed as percentages. The aspect ratio is calculated by dividing the tire’s height off the rim by its width by tire makers. When a tire’s aspect ratio is 65, its height is equal to 65% of its width. For instance, the 65 indicates that the height is 65% of the tire’s width in a tire of size P215/65 R15. A tire’s sidewall will be bigger the bigger the aspect ratio.

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A letter that denotes a type of internal construction maintaining the stability of your tire follows the aspect ratio. There are two different construction types that you could notice on a tire’s sidewall:

  • R: Radial
  • D or “B” or “- “– Diagonal or Bias Ply

The letter “R” will typically appear in the tire size designation because radial tires are the most popular tires today. In a tire with radial construction, the internal ply cords are arranged from one bead to the next in a radial pattern that is virtually perpendicular to the direction of rotation. The letters RF and ZR, which stand for run-flat and higher speed rating tires respectively, may also appear on occasion.

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Wheel Diameter

Wheel Diameter

The rim’s diameter code, expressed in inches, is the number that follows, which is where the tire can be placed. A tire with the dimensions P215/65 R15, for instance, would fit a rim with a 15-inch diameter.

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Some other things to know

Load Index: This shows the maximum load that the tire when inflated properly, can support. The tire sidewall will also list the maximum load in pounds and kilograms.

Speed Rating: This shows the maximum speed that a tire is capable of travelling. Frequently, speed ratings are matched to the vehicle’s top speed. For instance, a tire with an H-speed rating can travel at a top speed of 130 mph (210 km/h). it advises not to drive faster than the posted speed limit.

DOT Symbol: The letters “DOT” on the sidewall signify that it meets all relevant US Federal Motor Vehicle Safety Standards.

Tire Identification Number: This is the series of letters that come after the letter “DOT.” The TIN contains up to 12 numbers and letters to specify the factory, the week and year the tire was made, as well as the location of the plant.

UTQG: This stands for Uniform Tire Quality Grading, a classification system established by the U.S. Department of Transportation to inform consumers about tire options based on relative treadwear, traction, and temperature capabilities. The wet traction of a tire is shown by its traction grade in a controlled test. An “AA” rated tire provides exceptional traction in slick weather. Temperature ratings show how well a tire can endure and dissipate harmful heat. Higher temperature grade tires may function at faster speeds.

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Different types of tires sizes

There are many different types of tire sizes, and they can be represented in a variety of ways. Here are some of the most common ways that tire sizes are described:

  • Metric Tire Size
  • Alpha-Numeric Tire Size
  • P-Metric Tire Size
  • LT-Metric Tire Size
  • Numeric Tire Size

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Metric Tire Size

It uses a three-digit number for the tire’s width in millimetres, a two-digit aspect ratio to represent the tire’s height as a percentage of its width, and a letter to denote the kind of construction (R for radial). This is the most popular method for sizing tires.

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Alpha-Numeric Tire Size

In this earlier way of sizing tires, the width, aspect ratio, and rim diameter of the tire are denoted by a combination of letters and numbers.

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P-Metric Tire Size

This way of sizing tires is comparable to the metric system, but it adds a “P” to the beginning of the tire size to denote that it is intended for use on passenger cars.

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LT-Metric Tire Size

The only difference between this and the P-Metric system of tire sizing is the letter “LT” that is added to the beginning of the tire size to indicate that it is intended for use on light trucks.

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Numeric Tire Size

This older method for measuring tire dimensions uses a two-digit number to describe the tire’s width in inches, an additional two-digit number to represent its aspect ratio, and finally a letter to designate the type of construction of the tire.

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Tire size FAQs

What do the numbers on a tire size mean?

The number 215 denotes the tire’s width, which in this case is 215 millimetres from sidewall to sidewall. The ratio of its height to width is indicated by the aspect ratio code 65. This tire’s height is 65% of its width. R stands for radial construction. The wheel size is 15.

What do the 3 numbers mean on tire size?

TIRE WIDTH: The three-digit number that follows the letter indicates the tire’s width in millimetres (measured from side to side while looking at the tire from the front). The section width is another name for this. Aspect Ratio: C The two-digit aspect ratio is separated from the tire width value by a forward slash.

What does p265 70R17 mean?

The numbers 265/70R17 115T are shown by an arrow on the inner sidewall of the tire. The wheel diameter is 17, the aspect ratio is 70, R stands for radial, the breadth is 265 and the load index and speed symbol are 115T.

How wide is a 275 tire?

A tire size of 275/35 R19 indicates that the tire is 275mm (or 10.8 inches) wide.

What does r16 mean on tires?

The percentage of the tire width is used to represent this. The letter “R” stands for the tire’s method of construction, indicating that it is a radial tire. The wheel rim’s inch diameter is represented by the next two numbers (16).

What do 32 tires mean?

Good tire tread depth will be 6/32 or deeper; if it is 4/32 or less, you should start considering replacing your tires and getting new ones; and 2/32 or less indicates that you should change your tires as soon as possible.

What does 225 50 mean?

The tire section width, which is the measurement of the tire from sidewall to sidewall in millimetres, is designated by the number 225. The rim to which it is fitted determines how this measurement changes. (1-inch equals 25.4 millimetres). The two-figure aspect ratio is 50.

Can I put 55 tires instead of 50?

In terms of driving or handling, there aren’t many differences between tires in the 50 and 55 series. Depending on the composition and design of the tires themselves, you might not even notice a change. The new tire will be marginally higher and bigger in circumference.

How do I know my rim size?

You may find that on the inside of the driver’s door frame or on the sidewall of the tires on your original wheels. For further information, see Tire Size Explained (Reading the Sidewall). The fifth set of numbers and characters represents the wheel diameter (in inches or millimetres).

That Is all for this article, where we looked at how to read tire size. We also got to discuss the different types of tire sizes. Hope it was helpful. If so, kindly share it with others. Thanks for reading; see you around!