265/35R18 tyre size
A 265/35R18 tyre is 265 mm (10.4") wide with a sidewall height of 35 % of the width, i.e. 92.8 mm (3.7"), on a 18" (457 mm) rim. Overall diameter is 642.7 mm (25.3"), so the closest inch-style size is 25.3×10.4R18. Static circumference is 2019 mm; the ETRTO rolling circumference is 1960 mm, giving 510 revolutions per km (821 per mile).
Dimensions and rolling diameter
| Section width | 265 mm | 10.43″ |
| Sidewall height | 92.8 mm | 3.65″ |
| Rim diameter | 457.2 mm | 18″ |
| Overall diameter (static, unloaded) | 642.7 mm | 25.30″ |
| Static radius | 321.4 mm | 12.65″ |
| Static circumference (π × D) | 2,019 mm | 79.5″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,960 mm | 77.2″ |
| Effective rolling radius | 312.0 mm | 12.28″ |
| Revs per km (rolling / static) | 510 / 495 | |
| Inch equivalent | 25.3×10.4R18 | |
| Approved rim widths (approx.) | 9″–10.5″ (measuring rim 9.5″) | |
A 265/35R18 tyre is 265 mm (10.4") wide with a sidewall height of 35 % of the width, i.e. 92.8 mm (3.7"), on a 18" (457 mm) rim. Overall diameter is 642.7 mm (25.3"), so the closest inch-style size is 25.3×10.4R18. Static circumference is 2019 mm; the ETRTO rolling circumference is 1960 mm, giving 510 revolutions per km (821 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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