How to Read Your Tyre Size and Sidewall Markings
Every tyre carries a code moulded into its sidewall that tells you its exact size and capabilities. Knowing how to read it means you can order the correct replacement in seconds and check that the tyres already on your car are the right ones. Here is what each part of a marking like 205/55 R16 91V actually means.
The main size code, step by step
Take a typical marking of 205/55 R16 91V. Each element has a specific meaning that, together, describes the tyre precisely.
- 205: the width of the tyre in millimetres, measured across the tread
- 55: the aspect ratio, meaning the sidewall height is 55 per cent of the width
- R: radial construction, which almost every modern car tyre uses
- 16: the diameter of the wheel rim the tyre fits, in inches
- 91: the load index, a coded figure for the maximum weight the tyre can carry
- V: the speed rating, the maximum speed the tyre is approved for
Understanding the load index
The load index is a number that corresponds to a maximum weight each tyre can safely support. A load index of 91, for example, means each tyre can carry up to 615kg. Every vehicle has a minimum load index specified by the manufacturer, and you should never fit tyres rated below it, because they may not cope with the weight of your car when fully loaded.
Understanding the speed rating
The letter at the end is the speed rating, the maximum speed the tyre is designed to sustain when correctly inflated and loaded. A V rating is good for up to 149mph, an H rating for up to 130mph, and a Y rating for up to 186mph. You should always fit tyres that meet or exceed the rating your manufacturer specifies, even though UK speed limits are far lower, because the rating also reflects how the tyre handles heat and high-speed stability.
Other markings worth knowing
- XL: Extra Load, a reinforced tyre able to carry more weight than a standard version of the same size
- M+S: Mud and Snow, indicating some winter capability
- The snowflake symbol (3PMSF): certified for severe winter conditions
- DOT code: the last four digits show the week and year of manufacture, so 2523 means the 25th week of 2023
- Runflat markings such as RSC, ROF, or ZP, depending on the manufacturer
Why it matters when ordering tyres
When you call for a replacement, reading these markings to your fitter means you get exactly the right tyre first time, with no wasted journeys. It is also worth checking that all four tyres carry sensible, matching sizes and that none are older than recommended. If you are unsure, a mobile fitter can read the markings for you, confirm the correct specification for your vehicle, and supply and fit the right tyre at your location.
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