Tire Size Speedometer Calibrator
Calculate the speedometer error introduced when changing tire sizes. Enter stock tire size, new tire size, and a reference speed to see actual vs indicated speed.
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Applications
Compare stock and replacement tire sizes to determine how speedometer readings change with plus-size tire upgrades. Essential for automotive enthusiasts upgrading wheels, off-roaders fitting larger tires, and anyone ensuring their speedometer stays accurate after changing tire diameter.
Speedometer Calibration Formula
Tire diameter = rim_diameter_mm + 2 × (width × aspect_ratio / 100). Actual speed = reference_speed × (new_diameter / stock_diameter). Percentage error = ((new_diameter - stock_diameter) / stock_diameter) × 100. A difference exceeding 3% is generally not recommended as it affects speedometer accuracy, gearing, and ABS performance.
Fun Fact: Most factory speedometers are deliberately calibrated to read 2-5% higher than actual speed, so when your new tires increase your true speed, you might actually fix this intentional error instead of creating one!
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