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Tire size calculator
Enter a size like 205/55R16 to see its real dimensions — add a second size to compare fitment and speedometer effect.
Diameter
24.88 in · 631.9 mm
Sidewall
4.44 in · 112.8 mm
Circumference
78.2 in · 1,985.2 mm
Revs
811/mi · 504/km
A tire's marking encodes its geometry: width in millimeters, aspect ratio (sidewall height as a percent of width), and rim diameter in inches. Overall diameter drives everything else — gearing, speedometer accuracy, and whether the new setup clears the fender. A change under about 3% in diameter is the usual rule of thumb for staying close to stock behavior.