Speedometer Error: Summer to Winter Tires
Switching from summer to winter tires that are slightly smaller in diameter (e.g., 25.5 to 24.8 inches) causes a minor speedometer reading change.
How to use this tool
- Use the tire diameter calculator to find your original and new tire diameters.
- Enter both diameters and your speedometer reading.
- The result shows your true speed and the percentage speedometer error.
Winter tire sizes often differ slightly from summer fitments — calculate any speedometer discrepancy when swapping seasonal tires.
Frequently asked questions
- Does changing tire size affect the speedometer?
- Yes. A larger-diameter tire covers more ground per revolution, so the speedometer reads low — you're actually going faster than it shows. A smaller tire makes it read high.
- How much tire size difference is acceptable?
- Most states allow up to 3% speedometer error. Keep tire diameter within 3% of stock to avoid odometer, ABS, and traction control issues.