When you change tire sizes (diameter), your speedometer may become inaccurate. This tool calculates your actual speed compared to the speedometer reading when going from a stock tire size to a new tire size.
Speedometer Calibration Calculator
Enter your stock and new tire sizes to see your actual speed.
How It Works
Formula used: Actual Speed = (New Tire Diameter / Stock Tire Diameter) × Indicated Speed
If the new tire is taller, your speedometer will underreport. If it's shorter, it will overreport.
Why You Need It
Your speedometer is calibrated to the stock tire diameter. If you install larger or smaller tires, it can misreport your actual speed. This affects:
- Driving accuracy
- Radar trap risk
- Fuel economy readings
- Gear shifting (automatic vehicles)
How to Use
- Enter your stock tire diameter in inches
- Enter your new tire diameter in inches
- Type your current speedometer reading
- Instantly get your actual speed
Example
If your stock tires are 28" in diameter and your new tires are 30", at a speedometer reading of 60 mph, your actual speed is 64.29 mph.
Works With
- Passenger cars
- SUVs
- Trucks
- Off-road and lifted builds