The individual parts
- 225 – nominal width in millimetres. The real width depends on the rim width.
- 45 – aspect ratio: the sidewall is 45 % as tall as the tyre is wide.
- R – radial construction, the standard for passenger car tyres.
- 17 – rim diameter in inches. Tyre and rim must match exactly.
- 91 – load index: 615 kg capacity per tyre.
- W – speed rating: approved up to 270 km/h.
Calculating the overall diameter
The three dimensions give the diameter of the unloaded tyre:
Sidewall = 225 × 45 / 100 = 101.3 mm Diameter = 17 × 25.4 + 2 × 101.3 = 634.3 mm
Other markings
- XL / Reinforced – reinforced tyre with a higher load index.
- M+S and the alpine symbol (3PMSF) – winter or all-season capability.
- DOT code – the last four digits show production week and year (e.g. 2324 = week 23/2024).
- ZR – historic marking for above 240 km/h, today usually shown in addition to the speed rating.
Try it: enter your values in the calculator and see what changes live.
Open calculatorGeneral information without warranty – no legal advice. Vehicle documents, certificates and the inspector are authoritative.