225/45R17 tyre size
A 225/45R17 tyre is 225 mm (8.9") wide with a sidewall height of 45 % of the width, i.e. 101.3 mm (4.0"), on a 17" (432 mm) rim. Overall diameter is 634.3 mm (25.0"), so the closest inch-style size is 25×8.9R17. Static circumference is 1993 mm; the ETRTO rolling circumference is 1935 mm, giving 517 revolutions per km (832 per mile).
Dimensions and rolling diameter
| Section width | 225 mm | 8.86″ |
| Sidewall height | 101.3 mm | 3.99″ |
| Rim diameter | 431.8 mm | 17″ |
| Overall diameter (static, unloaded) | 634.3 mm | 24.97″ |
| Static radius | 317.2 mm | 12.49″ |
| Static circumference (π × D) | 1,993 mm | 78.5″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,935 mm | 76.2″ |
| Effective rolling radius | 307.9 mm | 12.12″ |
| Revs per km (rolling / static) | 517 / 502 | |
| Inch equivalent | 25×8.9R17 | |
| Approved rim widths (approx.) | 7″–8.5″ (measuring rim 7.5″) | |
A 225/45R17 tyre is 225 mm (8.9") wide with a sidewall height of 45 % of the width, i.e. 101.3 mm (4.0"), on a 17" (432 mm) rim. Overall diameter is 634.3 mm (25.0"), so the closest inch-style size is 25×8.9R17. Static circumference is 1993 mm; the ETRTO rolling circumference is 1935 mm, giving 517 revolutions per km (832 per mile).
Why two circumferences? The static figure is simple geometry (π × diameter). Under load a radial tyre flattens and rolls about 3 % less per revolution; ETRTO defines the rolling circumference as 3.05 × the nominal diameter, which is what manufacturers quote and what speedo and gearing calculations should use.
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