235/40R19 tyre size
A 235/40R19 tyre is 235 mm (9.3") wide with a sidewall height of 40 % of the width, i.e. 94.0 mm (3.7"), on a 19" (483 mm) rim. Overall diameter is 670.6 mm (26.4"), so the closest inch-style size is 26.4×9.3R19. Static circumference is 2107 mm; the ETRTO rolling circumference is 2045 mm, giving 489 revolutions per km (787 per mile).
Dimensions and rolling diameter
| Section width | 235 mm | 9.25″ |
| Sidewall height | 94.0 mm | 3.70″ |
| Rim diameter | 482.6 mm | 19″ |
| Overall diameter (static, unloaded) | 670.6 mm | 26.40″ |
| Static radius | 335.3 mm | 13.20″ |
| Static circumference (π × D) | 2,107 mm | 82.9″ |
| Rolling circumference (ETRTO 3.05 × D) | 2,045 mm | 80.5″ |
| Effective rolling radius | 325.5 mm | 12.82″ |
| Revs per km (rolling / static) | 489 / 475 | |
| Inch equivalent | 26.4×9.3R19 | |
| Approved rim widths (approx.) | 8″–9.5″ (measuring rim 8.5″) | |
A 235/40R19 tyre is 235 mm (9.3") wide with a sidewall height of 40 % of the width, i.e. 94.0 mm (3.7"), on a 19" (483 mm) rim. Overall diameter is 670.6 mm (26.4"), so the closest inch-style size is 26.4×9.3R19. Static circumference is 2107 mm; the ETRTO rolling circumference is 2045 mm, giving 489 revolutions per km (787 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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