235/45R17 tyre size
A 235/45R17 tyre is 235 mm (9.3") wide with a sidewall height of 45 % of the width, i.e. 105.8 mm (4.2"), on a 17" (432 mm) rim. Overall diameter is 643.3 mm (25.3"), so the closest inch-style size is 25.3×9.3R17. Static circumference is 2021 mm; the ETRTO rolling circumference is 1962 mm, giving 510 revolutions per km (820 per mile).
Dimensions and rolling diameter
| Section width | 235 mm | 9.25″ |
| Sidewall height | 105.8 mm | 4.16″ |
| Rim diameter | 431.8 mm | 17″ |
| Overall diameter (static, unloaded) | 643.3 mm | 25.33″ |
| Static radius | 321.7 mm | 12.66″ |
| Static circumference (π × D) | 2,021 mm | 79.6″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,962 mm | 77.2″ |
| Effective rolling radius | 312.3 mm | 12.29″ |
| Revs per km (rolling / static) | 510 / 495 | |
| Inch equivalent | 25.3×9.3R17 | |
| Approved rim widths (approx.) | 7.5″–9″ (measuring rim 8″) | |
A 235/45R17 tyre is 235 mm (9.3") wide with a sidewall height of 45 % of the width, i.e. 105.8 mm (4.2"), on a 17" (432 mm) rim. Overall diameter is 643.3 mm (25.3"), so the closest inch-style size is 25.3×9.3R17. Static circumference is 2021 mm; the ETRTO rolling circumference is 1962 mm, giving 510 revolutions per km (820 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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