225/50R16 tyre size
A 225/50R16 tyre is 225 mm (8.9") wide with a sidewall height of 50 % of the width, i.e. 112.5 mm (4.4"), on a 16" (406 mm) rim. Overall diameter is 631.4 mm (24.9"), so the closest inch-style size is 24.9×8.9R16. Static circumference is 1984 mm; the ETRTO rolling circumference is 1926 mm, giving 519 revolutions per km (836 per mile).
Dimensions and rolling diameter
| Section width | 225 mm | 8.86″ |
| Sidewall height | 112.5 mm | 4.43″ |
| Rim diameter | 406.4 mm | 16″ |
| Overall diameter (static, unloaded) | 631.4 mm | 24.86″ |
| Static radius | 315.7 mm | 12.43″ |
| Static circumference (π × D) | 1,984 mm | 78.1″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,926 mm | 75.8″ |
| Effective rolling radius | 306.5 mm | 12.07″ |
| Revs per km (rolling / static) | 519 / 504 | |
| Inch equivalent | 24.9×8.9R16 | |
| Approved rim widths (approx.) | 6″–8″ (measuring rim 7″) | |
A 225/50R16 tyre is 225 mm (8.9") wide with a sidewall height of 50 % of the width, i.e. 112.5 mm (4.4"), on a 16" (406 mm) rim. Overall diameter is 631.4 mm (24.9"), so the closest inch-style size is 24.9×8.9R16. Static circumference is 1984 mm; the ETRTO rolling circumference is 1926 mm, giving 519 revolutions per km (836 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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