245/40R17 tyre size
A 245/40R17 tyre is 245 mm (9.6") wide with a sidewall height of 40 % of the width, i.e. 98.0 mm (3.9"), on a 17" (432 mm) rim. Overall diameter is 627.8 mm (24.7"), so the closest inch-style size is 24.7×9.6R17. Static circumference is 1972 mm; the ETRTO rolling circumference is 1915 mm, giving 522 revolutions per km (840 per mile).
Dimensions and rolling diameter
| Section width | 245 mm | 9.65″ |
| Sidewall height | 98.0 mm | 3.86″ |
| Rim diameter | 431.8 mm | 17″ |
| Overall diameter (static, unloaded) | 627.8 mm | 24.72″ |
| Static radius | 313.9 mm | 12.36″ |
| Static circumference (π × D) | 1,972 mm | 77.6″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,915 mm | 75.4″ |
| Effective rolling radius | 304.7 mm | 12.00″ |
| Revs per km (rolling / static) | 522 / 507 | |
| Inch equivalent | 24.7×9.6R17 | |
| Approved rim widths (approx.) | 8″–9.5″ (measuring rim 8.5″) | |
A 245/40R17 tyre is 245 mm (9.6") wide with a sidewall height of 40 % of the width, i.e. 98.0 mm (3.9"), on a 17" (432 mm) rim. Overall diameter is 627.8 mm (24.7"), so the closest inch-style size is 24.7×9.6R17. Static circumference is 1972 mm; the ETRTO rolling circumference is 1915 mm, giving 522 revolutions per km (840 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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