215/50R17 tyre size
A 215/50R17 tyre is 215 mm (8.5") wide with a sidewall height of 50 % of the width, i.e. 107.5 mm (4.2"), on a 17" (432 mm) rim. Overall diameter is 646.8 mm (25.5"), so the closest inch-style size is 25.5×8.5R17. Static circumference is 2032 mm; the ETRTO rolling circumference is 1973 mm, giving 507 revolutions per km (816 per mile).
Dimensions and rolling diameter
| Section width | 215 mm | 8.46″ |
| Sidewall height | 107.5 mm | 4.23″ |
| Rim diameter | 431.8 mm | 17″ |
| Overall diameter (static, unloaded) | 646.8 mm | 25.46″ |
| Static radius | 323.4 mm | 12.73″ |
| Static circumference (π × D) | 2,032 mm | 80.0″ |
| Rolling circumference (ETRTO 3.05 × D) | 1,973 mm | 77.7″ |
| Effective rolling radius | 314.0 mm | 12.36″ |
| Revs per km (rolling / static) | 507 / 492 | |
| Inch equivalent | 25.5×8.5R17 | |
| Approved rim widths (approx.) | 6″–8″ (measuring rim 7″) | |
A 215/50R17 tyre is 215 mm (8.5") wide with a sidewall height of 50 % of the width, i.e. 107.5 mm (4.2"), on a 17" (432 mm) rim. Overall diameter is 646.8 mm (25.5"), so the closest inch-style size is 25.5×8.5R17. Static circumference is 2032 mm; the ETRTO rolling circumference is 1973 mm, giving 507 revolutions per km (816 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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