Metric Tire Codes
Tires & Wheels · 7 specs
Direct Answer
The ISO Metric Tire Code (standardized under ISO 4000-1 and ETRTO conventions, e.g. P225/45R17 91V) is the universal automotive tire sizing nomenclature. Decoding section width in millimeters, aspect ratio sidewall height percentage, internal radial carcass construction, wheel rim diameter in inches, load index, and maximum speed symbol.
Source: ISO 4000-1:2021 (Passenger car tyres and rims — Part 1: Tyres) / ETRTO Standards Manual / US DOT 49 CFR 571.109 · Last reviewed Aug 28, 2026
Specs
| Standardization | ISO 4000-1 / ETRTO (European Tyre and Rim Technical Organisation) / US Tire & Rim Association (TRA) |
| Prefix Designation | P: Passenger Car | LT: Light Truck (heavier plies) | ST: Special Trailer | T: Temporary Spare |
| Section Width (e.g. '225') | Nominal cross-sectional tire width in millimeters from sidewall to sidewall (225 mm) |
| Aspect Ratio / Profile (e.g. '45') | Sidewall section height expressed as a percentage of width (Height = 225 × 0.45 = 101.25 mm) |
| Internal Construction (e.g. 'R') | R: Radial ply cord orientation (90° to travel) | D / B: Bias ply / belted bias (historic) |
| Rim Diameter (e.g. '17') | Wheel rim bead seat diameter in whole inches (17.0 inches = 431.8 mm) |
| DOT Date Code | 4-digit oval stamp (e.g. '2422' = manufactured during the 24th week of 2022) |
Calculating Overall Tire Diameter
To calculate the total rolling diameter of a 225/45R17 tire:
- Sidewall Height: 225 mm × 0.45 = 101.25 mm
- Two Sidewalls: 101.25 mm × 2 = 202.5 mm
- Wheel Rim in mm: 17 inches × 25.4 mm/in = 431.8 mm
- Total Tire Diameter: 202.5 mm + 431.8 mm = 634.3 mm (24.97 in).