Tire size calculator
Decode a tyre size like 205/55 R16 — width in mm, sidewall height as a percentage, rim in inches — and compare two sizes to see the real diameter difference and what it does to your speedometer.
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Paste or type a full size like 205/55 R16 91V \u2014 it is decoded instantly.
How to read it
Tread width in millimetres, measured sidewall to sidewall.
Sidewall height as a percentage of the width — 55 means the sidewall is 55% of 205 mm.
R for radial construction, 16 for the rim diameter in inches.
Frequently asked
What does 205/55 R16 mean?
205 is the tread width in millimetres, 55 means the sidewall is 55% of that width, R stands for radial construction and 16 is the rim diameter in inches.
Can I fit a different tire size on my car?
Geometrically, stay within about ±3% of the original overall diameter. But also check the load index, speed rating, wheel-arch clearance and what your vehicle documents allow.
How does tire size affect my speedometer?
The speedometer counts wheel revolutions. A larger-diameter tire covers more ground per turn, so the speedo under-reads — this calculator shows exactly by how much.
See also: what 205/55R16 means · fit a different size?
Reading a tire size: the full breakdown
| Part | Meaning |
|---|---|
| 205 | Tire width in millimetres |
| 55 | Aspect ratio — sidewall height as % of width |
| R | Radial construction (standard on virtually all car tires) |
| 16 | Rim diameter in inches |
| 91V | Load index (91 = 615 kg) and speed rating (V = 240 km/h) |