How to read a tyre size

Every passenger car tyre has a code such as 205/55 R16 91V on its sidewall. It looks confusing at first, but each part has one clear meaning. Once you know how to read it, you can buy the right tyre and also check for yourself whether an alternative suggested by the tyre shop actually suits your car.

The parts of the code

Let's break down 205/55 R16 91V piece by piece.

205: Section width (mm)

The first number is the width of the tyre at its widest point, from sidewall to sidewall, in millimetres. 205 means a tyre 205 mm wide. On passenger cars this value usually ranges from 155 to 315. A wider tyre gives more grip, but fuel consumption and rolling noise also rise slightly.

55: Aspect (profile) ratio (%)

The number after the slash is the sidewall height as a percentage of the section width. Here the sidewall height is 55% of 205 mm, or about 113 mm. The smaller the ratio, the lower the sidewall: values such as 40 and 35 are found on sporty, firm-riding tyres. Values such as 65 and 70 are found on more comfortable tyres that cope better with potholes.

R: Construction type

R shows that the tyre has a radial construction. Almost all passenger car tyres sold today are radial. On old or special tyres you may see D (diagonal/cross-ply) or B (bias-belted). Some high-speed tyres also have a Z in front of the R (ZR), which indicates a speed rating above 240 km/h.

16: Rim diameter (inches)

The number after the R is the diameter of the wheel the tyre fits, in inches. If it says 16, the tyre can only be fitted to a 16-inch wheel. This value must match the wheel exactly; a close value will not do.

91: Load index

This number is a code for the maximum weight the tyre can carry at the recommended pressure. 91 means 615 kg per tyre. Four tyres together carry about 2,460 kg. The load index of a new tyre should not be lower than that of the car's original tyre. You can find the load index table in our separate guide.

V: Speed rating

The final letter shows the maximum speed the tyre can safely reach. V means 240 km/h. Other common ones: T (190), H (210), W (270), Y (300). Winter tyres may have a lower speed rating than the original tyre, but in that case you may be asked to place a notice inside the car showing the speed limit.

Other markings on the sidewall

• XL or Reinforced: A reinforced tyre. It has a higher load index than the standard version of the same size.
• M+S: A tread pattern designed for mud and snow. On its own it is not a guarantee of a winter tyre.
• 3PMSF (mountain and snowflake symbol): The mark of a true winter tyre that has passed a snow performance test.
• DOT code: The last four digits are the week and year of manufacture. For example, 2324 means week 23 of 2024.
• TWI: Shows where the tread wear indicator is located.
• Run Flat (such as RSC, ROF, ZP): A tyre that can travel a limited distance after a puncture.

Where to find the correct size for your car

The most reliable source is the tyre label on the edge of the driver's door. This label shows the sizes and pressures approved by the manufacturer. The owner's manual and the vehicle registration document also help. On Cars-Size you can select your make and model to see the factory sizes together with links to official sources.

Don't rely only on the size printed on the tyres currently fitted. A previous owner may have fitted a different size.

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