The numbers and letters stamped on the side of your tyre aren’t random. They tell you the exact size, how much weight the tyre can carry, and how fast it’s rated to travel. Learn to read them and you’ll never order the wrong tyre — or get caught out at MOT time.
Let’s decode a typical marking: 205/55 R16 91V.
Key Takeaways
- A marking like 205/55 R16 91V gives you width (mm), profile (%), construction, rim size (inches), load index and speed rating.
- The load index (91 = 615kg per tyre) and speed rating (V = 149mph) must meet or exceed your car’s requirements.
- In the UK the legal minimum tread depth is 1.6mm across the central three-quarters of the tyre (TyreSafe).
What do the numbers in a tyre size mean?
The size is the first block of characters, and it describes the tyre’s dimensions. In 205/55 R16, the 205 is the tyre width in millimetres, the 55 is the profile (sidewall height as a percentage of the width), and the 16 is the wheel rim diameter in inches.
The R between them stands for “radial”, the construction used by virtually all modern car tyres. Getting these three figures right matters: fit the wrong size and your speedometer reading, handling and even your MOT result can be affected. The correct sizes for your car are listed in your handbook and often on a sticker inside the driver’s door.
What is the tyre load index?
The load index is the two-digit number after the size — the 91 in our example — and it tells you the maximum weight each tyre can safely carry. A load index of 91 equals 615kg per tyre (Michelin).
You should always fit tyres with a load index that meets or exceeds your manufacturer’s recommendation. Going lower overloads the tyre and risks failure. Some tyres also carry an XL marking, meaning “Extra Load” — a reinforced casing for heavier vehicles or loads. If you tow or carry heavy loads, the load index is worth checking carefully.
What does the speed rating letter mean?
The final letter is the speed rating — the V in 205/55 R16 91V — and it shows the maximum speed the tyre is designed to sustain at full load. A V rating means up to 149mph (240km/h).
Like the load index, your replacement tyres should match or exceed the manufacturer’s specified speed rating, even though you’ll never legally reach those speeds on UK roads. The rating reflects the tyre’s heat resistance and build quality at speed, not a target. Common ratings include T (118mph), H (130mph), V (149mph) and W (168mph).
Which other tyre markings should you know?
Beyond size, load and speed, your sidewall carries safety and age information worth knowing. The most important for UK drivers is tread depth — the legal minimum is 1.6mm across the central three-quarters of the tyre, and tyres below that are an automatic MOT failure and a fine risk.
You’ll also find a DOT code showing the week and year the tyre was made, plus markings for the EU tyre label (fuel efficiency, wet grip and noise). The M+S symbol or a snowflake indicates winter or all-season capability. If you’re unsure whether your tyres are road-legal, our team can check your tyres in Aylesbury and advise on the right replacements.
Frequently Asked Questions
Can I fit a different tyre size to my car?
You should stick to the sizes recommended by your manufacturer, listed in your handbook or on the door-pillar sticker. Fitting a non-approved size can affect handling, your speedometer and your MOT result. If you want to change size, get expert advice first.
What is the legal tread depth for tyres in the UK?
The legal minimum tread depth is 1.6mm across the central three-quarters of the tyre and around its full circumference. Driving below this is an MOT failure and can mean a fine of up to £2,500 and three penalty points per tyre.
Do all four tyres need the same markings?
The two tyres on the same axle should match in size, load index and speed rating. It’s best practice for all four to match where possible, especially the speed rating, as mismatched tyres can affect handling, braking and stability.
The bottom line
Once you can read 205/55 R16 91V, buying tyres stops being guesswork — you’ll know the exact size, weight rating and speed rating your car needs. Match those to your manufacturer’s spec and keep an eye on that 1.6mm tread limit.
Need new tyres or a quick safety check? Book your tyres with Tyred & Exhausted in Aylesbury and we’ll fit the right ones for your car.