Speedometer Error from Worn vs New Tires
As tires wear down from 26 to 25.2 inches in diameter, your speedometer will read slightly higher than your actual speed.
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.
Worn tires have a smaller rolling diameter than new tires, which can make your speedometer read a little high — calculate the real speed difference here.
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.