285/70R17 tyre size
A 285/70R17 tyre is 285 mm (11.2") wide with a sidewall height of 70 % of the width, i.e. 199.5 mm (7.9"), on a 17" (432 mm) rim. Overall diameter is 830.8 mm (32.7"), so the closest inch-style size is 32.7×11.2R17. Static circumference is 2610 mm; the ETRTO rolling circumference is 2534 mm, giving 395 revolutions per km (635 per mile).
Dimensions and rolling diameter
| Section width | 285 mm | 11.22″ |
| Sidewall height | 199.5 mm | 7.85″ |
| Rim diameter | 431.8 mm | 17″ |
| Overall diameter (static, unloaded) | 830.8 mm | 32.71″ |
| Static radius | 415.4 mm | 16.35″ |
| Static circumference (π × D) | 2,610 mm | 102.8″ |
| Rolling circumference (ETRTO 3.05 × D) | 2,534 mm | 99.8″ |
| Effective rolling radius | 403.3 mm | 15.88″ |
| Revs per km (rolling / static) | 395 / 383 | |
| Inch equivalent | 32.7×11.2R17 | |
| Approved rim widths (approx.) | 8″–9.5″ (measuring rim 8.5″) | |
A 285/70R17 tyre is 285 mm (11.2") wide with a sidewall height of 70 % of the width, i.e. 199.5 mm (7.9"), on a 17" (432 mm) rim. Overall diameter is 830.8 mm (32.7"), so the closest inch-style size is 32.7×11.2R17. Static circumference is 2610 mm; the ETRTO rolling circumference is 2534 mm, giving 395 revolutions per km (635 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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