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Maintenance and tyres , Buying a used car , Know your car , Safety and breakdowns · Updated 2026-10-18

Reading a tyre label and sidewall markings

A tyre carries a lot of information, and most of it looks like a code. Knowing how to read it helps you buy the right replacement, avoid unsuitable tyres on a used car and compare offers fairly. You do not need to memorise it; you just need to know where to look and what each part tells you.

The size code

The main code on the sidewall looks like a row of numbers and letters, for example three digits, a slash, two digits, a letter, then two more digits. Reading from the left:

• First number: the width of the tyre in millimetres.
• Second number: the height of the sidewall as a percentage of the width, called the aspect ratio.
• Letter: the construction. R stands for radial, which is what nearly all modern car tyres are.
• Last number: the diameter of the wheel rim in inches.

Changing any of these changes the rolling circumference, which affects the speedometer, handling and sometimes clearance in the wheel arch. Use the size the maker approved, which appears in the manual and often on a sticker in the door frame. The tyre size tool shows how different sizes compare.

Load index and speed rating

After the size comes a number and a letter, such as two digits and a letter. The number is the load index: it shows the maximum weight one tyre can carry. The letter is the speed rating: the highest speed the tyre is designed to run at under proper conditions. You should never fit a tyre with a lower load index or speed rating than the maker requires. A higher one is usually fine, but may be stiffer or more expensive. These values mean the tyre was tested for specific limits, not that you should drive near them.

The date code

A small oval or rectangle contains the letters DOT and a series of characters. The last four digits show when the tyre was made: two digits for the week and two for the year. Tyres age even if they are not used, as the rubber hardens and cracks over time. When buying new tyres, check that they are not very old stock. On a used car, look at the date on every tyre, including the spare, and treat very old tyres as due for replacement even if the tread looks deep.

Season markings

• Summer tyres usually carry no special winter symbol and perform best in warm conditions.
• M+S means mud and snow, a basic marking about the tread design.
• A mountain with a snowflake symbol means the tyre has passed a defined snow-grip test. This is the more meaningful winter marking.
• All-season tyres try to work in a range of conditions, with compromises at the extremes.

Winter tyres have a softer compound that stays flexible in the cold. More about choosing and using them is in tyre basics and winter preparation.

The wear indicators

Small bars or ridges in the grooves of the tread show when the tyre has reached its minimum useful depth. Small arrows or letters on the sidewall point to where they are. The minimum legal depth differs by country, so check the local rule. Rather than wait for the limit, most experts suggest replacing tyres earlier, since grip in rain and snow drops as the tread gets shallow.

Other markings you may see

• Rotation arrows: the tyre is directional and must turn in that direction.
• Outside and inside: an asymmetric tyre must be fitted with the marked side facing out.
• XL or Reinforced: the tyre is built for a higher load.
• Run-flat symbols: the tyre can be driven for a limited distance with no pressure. These need a pressure monitoring system and special care.
• Maximum pressure: the highest pressure the tyre allows, not the recommended one. Use the figure from the car's sticker or manual.

The tyre label for comparing

New tyres in many markets come with a standard label that rates fuel efficiency, wet grip and noise. It is a convenient way to compare tyres of the same size. The ratings are measured under controlled conditions, so use them as a guide rather than a guarantee. Better wet grip is usually worth more than a small gain in efficiency, especially if you drive in rain often. Cheaper tyres can cost more in the long run if they wear out sooner, so think about the total cost, as discussed in the real cost of owning a car.

Checking tyres on a used car

When you buy, check that all four tyres match in size, make and type, the date codes are reasonable, and the wear is even. Mismatched or very worn tyres can be a clue to neglect, and you should add the replacement cost to your offer. A tyre bulge or cuts on the sidewall are reasons to walk away or replace the tyre immediately. Add tyres to your buying checklist.

Keeping it organised

Write down the size, load and speed codes and the purchase date of your tyres. In My Garage you can keep that information with your service records, so the next purchase is simple.

What to remember

• The size code gives width, profile, construction and rim diameter.
• Never go below the required load index and speed rating.
• The last four digits of the DOT code are the week and year of manufacture.
• The snowflake-on-mountain symbol is the real winter marking.
• Match tyres on a used car, and check age as well as tread.

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