What do the numbers on a tyre sidewall mean?
A code such as 205/55 R16 91V describes the tyre's dimensions, construction and limits. Each part means something specific, and matching them matters more than most drivers realise.
205 is the section width in millimetres — the distance across the tread from sidewall to sidewall.
55 is the aspect ratio: the sidewall height as a percentage of the width. Here the sidewall is 55% of 205mm, so about 113mm tall. A lower number means a shorter, stiffer sidewall, which sharpens handling and worsens ride comfort.
R means radial construction, which is what almost every modern car tyre uses.
16 is the wheel diameter in inches. This one is not a suggestion — the tyre must match the wheel exactly.
91 is the load index, a coded figure rather than a weight. 91 corresponds to 615kg per tyre. Fitting a lower index than the manufacturer specifies can overload the tyre.
V is the speed rating, again coded: V means 149mph. It is not permission to drive that fast; it describes the speed the tyre can sustain without structural failure, and insurers and testing regimes expect the rating to meet the vehicle's specification.
Two further markings matter. M+S means mud and snow, which is a manufacturer's self-declaration with no test behind it. The three-peak mountain snowflake symbol is different: it certifies the tyre passed a standardised snow traction test, and in countries with winter tyre laws it is usually that symbol, not M+S, that satisfies the requirement.
Elsewhere on the sidewall you will find a four-digit DOT date code — "3223" means the 32nd week of 2023. Rubber hardens with age regardless of tread depth, and many manufacturers advise replacement after six years and against using tyres over ten years old, however new they look.