[TireFitLab](https://tirefitlab.com/) › [Tire & wheel reference guides](https://tirefitlab.com/learn/) › How to read a tire size # 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; RF = run-flat (optional suffixes). ## 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. Tire size ### 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 RF (optional) | `P205/55R16 91V XL` | XL (Extra Load) or reinforced — higher maximum inflation pressure and load capacity. RF or RFT = run-flat — can be driven 80 km at 80 km/h after puncture. | ## Detailed reference pages Choose a common value or size to open its calculated data and explanation. - [91V](https://tirefitlab.com/learn/service-description/91v/) - [94V](https://tirefitlab.com/learn/service-description/94v/) - [95W](https://tirefitlab.com/learn/service-description/95w/) - [98W](https://tirefitlab.com/learn/service-description/98w/) - [100Y](https://tirefitlab.com/learn/service-description/100y/) - [102H](https://tirefitlab.com/learn/service-description/102h/) - [103V](https://tirefitlab.com/learn/service-description/103v/) - [105W](https://tirefitlab.com/learn/service-description/105w/) [Tire size calculator](https://tirefitlab.com/tire-size-calculator/) · [Tire type guide — P, LT, metric, radial & flotation](https://tirefitlab.com/learn/tire-types/) · [Tire load index chart](https://tirefitlab.com/learn/load-index/) · [Tire speed rating chart](https://tirefitlab.com/learn/speed-rating/) · [Tire & wheel reference guides](https://tirefitlab.com/learn/) Seasonal check ## Planning a long summer drive? Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter. [Estimate tire budget](https://tirefitlab.com/tire-budget-calculator/) ## More in this topic: Size validation Decode markings, compare sizes, and understand diameter, load and speed changes. - [**Tire type guide — P, LT, metric, radial & flotation** What do the letters in a tire size mean? P, LT, metric, radial (R) and flotation tire types explained.](https://tirefitlab.com/learn/tire-types/) - [**Tire sidewall markings decoder** Complete guide to every marking on a tire sidewall: size string, construction code, load index, speed rating, DOT date, M+S, 3PMSF snowflake, UTQG, max pressure, country of manufacture, and brand-specific symbols.](https://tirefitlab.com/learn/tyre-sidewall-markings/) - [**Tire load index chart** Use the tire load index chart to convert ratings 60–130 into kg and lb, then verify the vehicle placard and axle-load requirements.](https://tirefitlab.com/learn/load-index/) - [**Tire speed rating chart** Use the tire speed rating chart to convert symbols from L to Y/ZR into km/h and mph for replacement tire checks.](https://tirefitlab.com/learn/speed-rating/) ### Useful tools [Tire size converter (mm ↔ inches)](https://tirefitlab.com/tire-size-converter/)[Tire size calculator](https://tirefitlab.com/tire-size-calculator/) ### Content updated 2026-06-28 What changed - Checked generated routes, metadata, sitemap inclusion and localized page rendering. [Methodology](https://tirefitlab.com/methodology/)