245/40R19 tyre size
A 245/40R19 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 19" (483 mm) rim. Overall diameter is 678.6 mm (26.7"), so the closest inch-style size is 26.7×9.6R19. Static circumference is 2132 mm; the ETRTO rolling circumference is 2070 mm, giving 483 revolutions per km (778 per mile).
Dimensions and rolling diameter
| Section width | 245 mm | 9.65″ |
| Sidewall height | 98.0 mm | 3.86″ |
| Rim diameter | 482.6 mm | 19″ |
| Overall diameter (static, unloaded) | 678.6 mm | 26.72″ |
| Static radius | 339.3 mm | 13.36″ |
| Static circumference (π × D) | 2,132 mm | 83.9″ |
| Rolling circumference (ETRTO 3.05 × D) | 2,070 mm | 81.5″ |
| Effective rolling radius | 329.4 mm | 12.97″ |
| Revs per km (rolling / static) | 483 / 469 | |
| Inch equivalent | 26.7×9.6R19 | |
| Approved rim widths (approx.) | 8″–9.5″ (measuring rim 8.5″) | |
A 245/40R19 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 19" (483 mm) rim. Overall diameter is 678.6 mm (26.7"), so the closest inch-style size is 26.7×9.6R19. Static circumference is 2132 mm; the ETRTO rolling circumference is 2070 mm, giving 483 revolutions per km (778 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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