Speedometer Error & Tire Size Calculator
See how your real speed and odometer change when you change tire size.
Stock tire (e.g. 215/60R16)
New tire
Stock diameter
26.16 in
New diameter
26.74 in
Speedo error
+2.24%
Actual speed at 60 mph indicated
61.35 mph
Odometer drift
+2.24% (reads MORE miles than actual)
Minor offset, within typical OEM tolerance for production cars.
Diameter = 2 × sidewall (mm / 25.4) + wheel diameter. Negative % means new tire is smaller — actual speed is lower than indicated.
About this tool
Enter stock and new tire sizes (width, aspect ratio, wheel diameter). Get the speedometer error %, the actual speed at 60 mph indicated, and the odometer discrepancy over a year. Targets the r/cars, r/Truck, r/4x4, and r/Subaru recurring 'will my speedometer be off' question when changing tire size.
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