Your tyre size is printed on the sidewall, something like 205/55 R16 91V. Each part tells you a specific dimension or rating, and getting them right matters for safety, handling and the law. Once you can read it, ordering the correct tyre, or checking a fitter has quoted the right one, takes seconds. Here's how to decode it.
Breaking down 205/55 R16 91V
Read left to right, each character is a separate piece of information about the tyre's size and limits:
- 205 – tread width in millimetres.
- 55 – the profile or aspect ratio: sidewall height as a percentage of width (here 55% of 205mm).
- R – radial construction, used on almost all modern car tyres.
- 16 – wheel rim diameter in inches.
- 91 – the load index (maximum weight per tyre).
- V – the speed rating (the maximum speed the tyre is rated for).
So a 205/55 R16 91V is 205mm wide, with a sidewall 55% of that, on a 16-inch radial wheel, rated to carry 615kg per tyre at up to 149mph. Change any of those numbers and you change how the tyre fits and behaves.
Where to find the right size
Read it off the existing tyre sidewall, or check the placard in the driver's door shut, inside the fuel filler flap, or in the handbook. The car's recommended size is the safe reference, which matters especially if a previous owner fitted the wrong tyres. If the sidewall and the placard disagree, trust the placard, because that's the manufacturer's specification for your car.
The extra markings to know
Beyond the core size, the sidewall carries a few other markings worth recognising:
- XL or Reinforced – an extra-load tyre with a higher weight capacity, common on SUVs, vans and EVs.
- The DOT date code – the four digits showing the week and year of manufacture, key for checking tyre age.
- M+S or the 3PMSF snowflake – mud and snow or certified winter grip, relevant for winter and all-season tyres.
- A directional arrow – meaning the tyre must rotate one way, which affects how it can be rotated.
Why you shouldn't mix sizes
Fitting a different width, profile or rim size changes the rolling diameter, which can upset the speedometer, ABS and stability systems, and may fail the MOT. UK law also restricts mixing tyres of different construction on the same axle, and the rules on tyre safety (GOV.UK) set out the basics. Stick to the manufacturer's specification unless you've taken expert advice, because even a small change can have knock-on effects you won't notice until an emergency stop.
Not sure? We'll match it for you
Tell us your registration or read us the sidewall and we'll source the correct tyre, no guesswork. Our mobile fitting service brings the right size to your door across the UK. Book a fit.
