How to Read a Tyre Size
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In short
A tyre size like 205/55 R16 91V reads: width in mm / sidewall as % of width, R for radial, rim inches, then load index and speed rating.
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The size code, part by part
Take 205/55 R16 91V — the most common size on UK compact hatchbacks:
| Part | Meaning |
|---|---|
| 205 | Section width in millimetres |
| 55 | Aspect ratio — the sidewall is 55% of 205 mm (113 mm) |
| R | Radial construction |
| 16 | Rim diameter in inches |
| 91 | Load index — 615 kg per tyre |
| V | Speed rating — 149 mph maximum |
Every size in our reference has its own page with computed diameter, circumference and ±3% alternative sizes — try 205/55 R16 or browse all sizes. To confirm what your car left the factory with, look up your car's full specs, including OE tyre sizes, at 247VehicleCheck.
Tyre Owner Essentials
Other sidewall markings
XL means extra load (a higher load index for the same size). RF/ROF/RSC variants mean run-flat. M+S is a mud-and-snow marking; the 3PMSF snowflake symbol is the proper winter certification. A brand-specific code like MO or * means the tyre was homologated for a particular manufacturer.
While you're at the sidewall, check the DOT date code — tyre age matters as much as tread.
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What do the numbers on a tyre mean?
In 205/55 R16 91V: 205 is width in mm, 55 is sidewall height as a percentage of width, R is radial, 16 is rim diameter in inches, 91 is the load index (615 kg) and V is the speed rating (149 mph).
Where do I find my tyre size?
On the tyre sidewall, on the placard inside the driver's door, and in the vehicle handbook. The placard is the authority for what your car should run.
Related pages on this site
Last updated:
Data: computed reference values (ETRTO tyre-size arithmetic), build date 5 September 2026. Reference only — always follow your vehicle manufacturer's placard or handbook.