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How to read tyre specs and understand markings on the sidewall 

A tyre’s sidewall is pretty much what it sounds like – the outer and inner “walls” on the sides of a tyre. This area of a tyre isn’t just printed with random characters and  markings. They are a gold mine of information that can help you make informed decisions when buying new tyres or maintaining them.

Why tyre markings matter

Knowing how to read tyre markings will help you with:

  • Ensuring your tyre can handle your vehicle's weight. 
  • Keeping track of your tyre’s age. 
  • Knowing your tyre’s speed capabilities. 
  • Comparing tyres across different brands when buying new tyres. 
  • Understanding your tyre's longevity, especially if you drive frequently. 
  • Staying safe on the road.
     

Don’t worry! You don’t have to be a tyre specialist to know how to read tyre specs from the markings. We'll break it down into four easy-to-digest sections: 

1. Tyre specs

Think of this section as your tyre's ID card. It tells you the fundamental characteristics of your tyre. Let's use example tyre codes: P 255/55 R 18 97T

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Tyre type

The letter at the beginning of a tyre size indicates the type of vehicle the tyre is designed for. For example, P is for passenger cars. LT is for light trucks, vans, and pickup trucks, T is for temporary spare tyres, and ST for special trailers. If your tyre has no preceding letter here, that means it’s a euro “metric” size.

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Tyre width

Also called “section width”, these tyre codes (255 here) refer to the nominal width of the tyre (or thickness) in millimetres. This measurement is taken from a tyre’s widest point of its outer sidewall to the widest point of its inner sidewall. Tyre width is measured in millimetres because it originated in Europe, which uses the metric system. Some off road tyres could use imperial units (31 x 10.50 R15). In this case, 31 is the overall diameter of the tyre. 10.5 is the width of the tyre.

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Aspect ratio

The tyre code after the slash is the tyre’s aspect ratio. This shows the height of the tyre's sidewall compared to its width. In this example, the sidewall height of the tyre is 55% of its width. The lower the ratio, the smaller the sidewall height, which means better cornering, but a rougher ride.

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Construction

The R in this example means “radial.” Almost every tyre on the road has radial construction, which means the cords of the carcass plies inside the tyre “radiate” directly across from one side of the tyre to the other. Other letters used are D, for diagonal construction, and B, for belted.

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Wheel diameter

This number (in inches) indicates that the tyre is designed to fit on a wheel with an 18-inch diameter.

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Load index

This indicates how much weight the tyre is certified to carry at maximum safe inflation. For example, a load index of 97 does not mean 97 pounds, but corresponds to a load capacity of 1,609 pounds.

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Speed rating

This indicates the maximum safe speed at which a tyre is certified to carry a load under specified conditions. Tyre speed ratings range from A (lowest) to Y (highest), with one exception: H falls between U and V. Therefore, you should not exceed the speed limit indicated in that chart for your safety.

2. DOT code

This assures that your tyre complies with all Department of Transportation (DOT) safety standards, which is required for US market requirements. After the DOT code is your tyre’s identification number, which begins with the tyre’s manufacturer and plant code where the tyre was manufactured (two numbers or letters). The ninth and tenth characters tell the week the tyre was manufactured. The last two numbers tell the year the tyre was manufactured. So, you will know how old your tyre is by reading the DOT code.

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DOT

Department of Transportation safety code

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B9

Tyre's manufacturer and plant code

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YR

Denotes tyre size

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UJNX

Optional characters that identify the brand and other significant characteristics of the tyre

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50

Denotes the week the tyre was produced. Number 5008 means it was manufactured in the 50th week of the year 2008

3. UTQG code

The Uniform Tire Quality Grading (UTQG) was established by the National Highway Traffic Safety Administration (NHTSA) in the US to evaluate tyres using standardised government tests and then grade each tyre on three main factors:

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  • Treadwear: This is the treadwear rating of the tyre, comparable only to other tyres within the same brand. A grade of 100 is the baseline. Higher number indicates longer tread life. Therefore a tyre with 200 treadwear rating should last twice as long compared to a tyre with a rating of 100. 
  • Traction: Traction grades are AA, A, B and C (with AA being the highest grade). They show how well a tyre stops on wet roads as measured on a specified government track. Any tyre rated under C is not safe for road travel. 
  • Temperature: The tyre's ability to dissipate heat is graded A, B, and C, from highest to lowest, under controlled indoor test conditions. Any tyre rated below C is considered unacceptable. 

4. Special symbols

Some tyres have unique benefits, as showcased with special symbols. For example, a Three-Peak Mountain Snowflake (3PMSF) symbol tells you that the tyre is certified to drive in extreme condition. This symbol is required for winter tyres and it’s also featured on some all-season and all-terrain tyres.

Additional markings

Here are a few examples of additional markings you can find on the tyre sidewall:

  • Tubeless: This indicates that the tyre has no tubes. A tubeless tyre is lighter, more fuel efficient, and more reliable in case of damage. 
  • Max Inflation or Max Press: It indicates the maximum amount of tyre inflation allowed. However, it’s not recommended to inflate your tyre to the limit because it will be too stiff and prone to damage from potholes, kerbs, or debris. 
  • SSR: It means the tyre is a “Self-Supporting Run-flat tyre” which can continue to be used after pressure loss thanks to its reinforced wall structure. 
  • Rotation: This marking is presented with an arrow pointing to the correct mounting direction. You can find this marking on directional tyres where their tread blocks, grooves, and sipes are designed to roll in only one direction. 
  • M+S: This symbol stands for “mud and snow ", meaning the tyre with this marking can be used on muddy and snowy roads. However, this doesn’t necessarily provide proof of passing an objective test.

 

Prepare for the road ahead

Understanding tyre specifications is important for maintaining your vehicle's safety and performance. By familiarising yourself with tyre markings and knowing how to read tyre specs, you can drive more safely and maximise your tyres’ potential. If you want to know which tyres are compatible with your vehicle or are confused about specific tyre details, always check your vehicle's manual or consult a professional.

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