How to read tyre sizes: a plain-English UK guide

Every car tyre sold in the UK has its size printed on the sidewall in a standard format. Once you've decoded it, picking the right replacement is straightforward.

A worked example: 205/55 R16 91V

• 205 — the tyre width in millimetres, sidewall to sidewall.
• 55 — the aspect ratio: sidewall height as a percentage of the width. Here 55% of 205mm.
• R — radial construction. Almost every car tyre sold today is radial.
• 16 — the rim diameter the tyre fits, in inches.
• 91 — the load index. 91 = 615 kg per tyre maximum load.
• V — the speed rating. V = up to 149 mph / 240 km/h.

Where to find the right size for your car

The manufacturer's recommended size is printed on a sticker inside the driver's door frame, inside the fuel filler flap, or in the handbook. The current tyre on the car is the next best source — but only if you know the previous owner didn't fit the wrong size.

Can I fit a different size?

You can fit any size listed in the vehicle handbook. Going up or down beyond that changes the rolling diameter, throws the speedo out, and can affect your insurance. If you want wider rubber or a plus-size alloy, check the manufacturer's approved list first.

What about XL, RF, or run-flats?

• XL or RF (reinforced): a stronger sidewall, often required on heavier cars and most EVs.
• RFT, ZP, SSR (run-flat): can be driven on at limited speed and distance after a puncture. Usually can't be repaired safely.
• M+S or 3PMSF: rated for mud and snow, or for severe winter conditions respectively.

When in doubt, send us a photo of the sidewall on WhatsApp with your registration. We'll confirm the correct fitment and quote on the spot.