225/55R16 tyre size
A 225/55R16 tyre is 225 mm (8.9") wide with a sidewall height of 55 % of the width, i.e. 123.8 mm (4.9"), on a 16" (406 mm) rim. Overall diameter is 653.9 mm (25.7"), so the closest inch-style size is 25.7×8.9R16. Static circumference is 2054 mm; the ETRTO rolling circumference is 1994 mm, giving 501 revolutions per km (807 per mile).
Dimensions and rolling diameter
| Section width | 225 mm | 8.86″ |
| Sidewall height | 123.8 mm | 4.87″ |
| Rim diameter | 406.4 mm | 16″ |
| Overall diameter (static, unloaded) | 653.9 mm | 25.74″ |
| Static radius | 327.0 mm | 12.87″ |
| Static circumference (π × D) | 2,054 mm | 80.9″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,994 mm | 78.5″ |
| Effective rolling radius | 317.4 mm | 12.50″ |
| Revs per km (rolling / static) | 501 / 487 | |
| Inch equivalent | 25.7×8.9R16 | |
| Approved rim widths (approx.) | 6″–8″ (measuring rim 7″) | |
A 225/55R16 tyre is 225 mm (8.9") wide with a sidewall height of 55 % of the width, i.e. 123.8 mm (4.9"), on a 16" (406 mm) rim. Overall diameter is 653.9 mm (25.7"), so the closest inch-style size is 25.7×8.9R16. Static circumference is 2054 mm; the ETRTO rolling circumference is 1994 mm, giving 501 revolutions per km (807 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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