255/70R16 tyre size
A 255/70R16 tyre is 255 mm (10.0") wide with a sidewall height of 70 % of the width, i.e. 178.5 mm (7.0"), on a 16" (406 mm) rim. Overall diameter is 763.4 mm (30.1"), so the closest inch-style size is 30.1x10R16. Static circumference is 2398 mm; the ETRTO rolling circumference is 2328 mm, giving 429 revolutions per km (691 per mile).
Dimensions and rolling diameter
| Section width | 255 mm | 10.04″ |
| Sidewall height | 178.5 mm | 7.03″ |
| Rim diameter | 406.4 mm | 16″ |
| Overall diameter (static, unloaded) | 763.4 mm | 30.06″ |
| Static radius | 381.7 mm | 15.03″ |
| Static circumference (π × D) | 2,398 mm | 94.4″ |
| Rolling circumference (ETRTO 3.05 × D) | 2,328 mm | 91.7″ |
| Effective rolling radius | 370.6 mm | 14.59″ |
| Revs per km (rolling / static) | 429 / 417 | |
| Inch equivalent | 30.1x10R16 | |
| Approved rim widths (approx.) | 7″–8.5″ (measuring rim 7.5″) | |
A 255/70R16 tyre is 255 mm (10.0") wide with a sidewall height of 70 % of the width, i.e. 178.5 mm (7.0"), on a 16" (406 mm) rim. Overall diameter is 763.4 mm (30.1"), so the closest inch-style size is 30.1x10R16. Static circumference is 2398 mm; the ETRTO rolling circumference is 2328 mm, giving 429 revolutions per km (691 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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