Compare tire sizes, calculate diameter, width, and speedometer error when changing tire dimensions.
A tire marked 225/45R17 means: 225mm width, 45% aspect ratio (sidewall height = 45% of width), R = Radial, 17" rim diameter.
Yes. Larger tires cover more ground per revolution, so your speedometer reads slower than actual speed. A 3% increase in diameter means at an indicated 60 mph, you are actually going 61.8 mph.
No. Check your owner manual or door jamb sticker for approved sizes. Extreme size changes can rub fenders, overload bearings, or void warranties.
Enter your current and proposed tire sizes (width/aspect ratio/rim diameter format). The calculator compares diameters, circumferences, speedometer error, and ground clearance.
Tire Diameter = Rim + 2 Γ Sidewall. Sidewall = Width (mm) Γ Aspect Ratio / 25.4. Speedometer error = (New Diameter / Old Diameter β 1) Γ 100%.
Upgrading from 225/65R17 to 245/65R17: Diameter increases 0.55" (+1.9%). Speedometer at 60 mph reads 58.9 mph actual. Ground clearance increases 0.28".
Keep speedometer error under 3% to avoid legal issues and maintain accurate speed readings. Larger tires reduce acceleration and fuel economy but improve ground clearance and ride comfort. Check for clearance issues before upsizing.