What do these numbers mean?

In the UK, the numbers on a tyre’s sidewall follow exactly the same international standard used
in many countries, including Europe and the US. These numbers provide information about the
tyre’s size, type, and performance characteristics.
Here’s what the numbers mean:

  1. Tyre Width (e.g., “205”)
     Example: In “205/55R16,” the “205” refers to the tyre’s width in millimetres.
     Meaning: This is the width of the tyre from sidewall to sidewall, measured in
    millimetres.
  2. Aspect Ratio (e.g., “55”)
     Example: In “205/55R16,” the “55” refers to the aspect ratio.
     Meaning: This number is a percentage that represents the height of the tyre’s sidewall as
    a percentage of the tyre’s width. In this case, the sidewall height is 55% of 205 mm.
  3. Tyre Construction (e.g., “R”)
     Example: In “205/55R16,” the “R” stands for radial construction.
     Meaning: This letter indicates the construction of the tyre. “R” means radial, which is the
    most common type of tyre construction. Other types include “D” for diagonal or bias-ply
    and “B” for belted bias.
  4. Rim Diameter (e.g., “16”)
     Example: In “205/55R16,” the “16” refers to the diameter of the wheel rim in inches.
     Meaning: This number tells you the diameter of the wheel that the tyre is designed to fit.
  5. Load Index (e.g., “91”)
     Example: In “205/55R16 91V,” the “91” is the load index.
     Meaning: The load index is a numerical code that indicates the maximum load the tyre
    can carry at the maximum speed. Higher numbers mean a greater load-carrying capacity.
  6. Speed Rating (e.g., “V”)
     Example: In “205/55R16 91V,” the “V” is the speed rating.
     Meaning: This letter indicates the maximum speed at which the tyre can carry the load
    indicated by the load index. For example, “V” corresponds to 149 mph (240 km/h).

Example:
In a tyre marked “205/55R16 91V”:
 205 = Tyre width in millimetres.
 55 = Aspect ratio (sidewall height is 55% of the tyre’s width).
 R = Radial construction.
 16 = Rim diameter in inches.
 91 = Load index (indicating the load capacity).
 V = Speed rating (maximum speed rating of 149 mph or 240 km/h).
The format and meaning of these numbers are standardized, so they apply universally, including
in the UK.

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