How to read a tire size
What does P205/55R16 91V mean?
P = passenger vehicle (optional). 205 = section width in mm. 55 = aspect ratio (sidewall = 55% of width). R = radial construction. 16 = rim diameter in inches. 91 = load index (615 kg per tire). V = speed rating (up to 240 km/h). XL = extra load.
How-to steps
- Find the size string Read the full sidewall marking from left to right, including service prefix, width, aspect ratio, construction, rim diameter, load index, and speed symbol.
- Decode the metric fields Convert width, aspect ratio, and rim diameter into sidewall height and overall diameter before comparing it with another size.
- Check service description Confirm load index and speed symbol meet or exceed the vehicle requirement before fitting.
Decode a tire size
Type the main sidewall size string to see the width, profile and sidewall math.
- Section width
- 225 mm
- Aspect ratio
- 45%
- Sidewall height
- 101.3 mm
- Overall diameter
- 634.3 mm
Reference-table value only. Always match your vehicle placard and tire sidewall markings.
Worked examples
Metric and flotation markings look different, but the table is calculated from the same nominal diameter, width and rim-size rules.
| Size | Overall diameter | Section width | Sidewall | Circumference |
|---|---|---|---|---|
| 225/45R17 | 24.97 in / 634 mm | 8.86 in / 225 mm | 3.99 in / 101.3 mm | 78.45 in / 1993 mm |
| 285/75R16 | 32.83 in / 834 mm | 11.22 in / 285 mm | 8.42 in / 213.8 mm | 103.14 in / 2620 mm |
| 33x12.50R15 | 33.00 in / 838 mm | 12.50 in / 318 mm | 9.00 in / 228.6 mm | 103.67 in / 2633 mm |
What to do with it: Round marketing sizes can hide several millimetres of difference.
P205/55R16 91V — field by field
| Field | Example | Spec |
|---|---|---|
| P | P205/55R16 91V | Vehicle type prefix. P = passenger. LT = light truck. No prefix = Euro-metric. Optional — most EU tires omit it. |
| 205 | P205/55R16 91V | Section width in millimetres. The widest point of the tire when properly inflated and mounted on the specified rim. |
| 55 | P205/55R16 91V | Aspect ratio — sidewall height as a percentage of the section width. A 205mm wide tire with a 55 ratio has a 112.75mm tall sidewall (205 × 0.55). |
| R | P205/55R16 91V | Construction type. R = radial (standard on all modern passenger tires). D = diagonal/bias-ply (rare; trailers, some off-road). B = bias-belted. |
| 16 | P205/55R16 91V | Rim (wheel) diameter in inches. The tire must match the rim diameter exactly. |
| 91 | P205/55R16 91V | Load index — the maximum load capacity per tire. 91 = 615 kg. Used in pairs: for a 1,500 kg axle load you need 2 × 750 kg, so LI ≥ 97. |
| V | P205/55R16 91V | Speed rating — the maximum sustained speed. V = 240 km/h. Common ratings: T=190, H=210, V=240, W=270, Y=300 km/h. |
| XL or RFT (optional) | P205/55R16 91V XL | A reinforced or extra-load tire variant. Use the complete load index, approved tire data and vehicle instructions; the letters alone do not set a universal inflation pressure. Run-flat codes depend on the exact product. Follow the tire and vehicle makers for drive-on limits and repairability. UN R117 — XL / Reinforced · Bridgestone — Run-flat FAQ |
As a manufacturer-specific example, Bridgestone describes a low-pressure speed limit of 50 mph (80 km/h). The sidewall distance limit controls; if none is marked, consult the vehicle manual. The FAQ says not to exceed 50 miles (80 km) when in doubt. Test maximums can differ in real use and are not guaranteed remaining range.
Source: Bridgestone — Run-flat: identification, TPMS, speed/distance, application
Detailed reference pages
Choose a common value or size to open its calculated data and explanation.
Tire size calculator · Tire type guide — P, LT, metric, radial & flotation · Tire load index chart · Tire speed rating chart · Tire & wheel reference guides
Sources checked for the cited claims: 2026-09-30
Seasonal check
Winter tire rules coming up?
Check tread depth, markings and local winter requirements before the first cold spell instead of waiting for the appointment rush.