The markings on a tyre sidewall contain everything you need to buy the right replacement and to know how old the current one is.
The main sequence
Something like 205/55 R16 91V.
205 is the width in millimetres.
55 is the aspect ratio – the sidewall height as a percentage of the width. Lower numbers mean a shorter sidewall, which typically means sharper handling and a firmer ride.
R indicates radial construction, which is essentially all modern tyres.
16 is the wheel diameter in inches, which is the one imperial holdout in an otherwise metric string.
Load and speed
91 is the load index, corresponding to a maximum weight per tyre from a standard table.
V is the speed rating, also from a table. Fitting a lower rating than the vehicle specifies can invalidate insurance.
Neither should be reduced below what the manufacturer specifies.
The date code
A four-digit number in an oval, usually preceded by other characters. The first two digits are the week, the last two the year. So 2224 means the twenty-second week of 2024.
Rubber degrades with age regardless of tread depth. Many manufacturers suggest replacement after several years even if the tread is legal, and a tyre near ten years old should be replaced.
Check this when buying tyres – stock sitting in a warehouse for years is sold as new.
What to match
The vehicle manufacturer’s specification, which is on a plate in the door frame or fuel flap.