---
title: Why is my speedometer off after changing tire size?
description: If you changed to a significantly different tire diameter than your factory size, your speedometer may read inaccurately.
---
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# Why is my speedometer off after changing tire size?
## A speedometer that reads inaccurately after a tire size change is caused by the difference in circumference between your new and factory tires. The bigger the size difference, the more noticeable the inaccuracy. A tuner, programmer, or shop recalibration can quickly correct the issue.
If you changed to a significantly different tire diameter than your factory size, your speedometer may read inaccurately. Here is why:
Your speedometer calculates speed based on rotations per unit of distance. A larger tire covers more ground per rotation, so the speedometer reads slightly low. A smaller tire does the opposite. Minor size changes stay very close to accurate; larger changes -- such as going from 235/55R18 to 265/70R18 -- create a more noticeable discrepancy.
**How to fix it:** Most modern vehicles can be recalibrated with an OBD-II device, programmer, or through a dealer. Some vehicles allow recalibration through the instrument cluster settings. Check your owner's manual for the correct process.
If you are concerned about the impact of a size change before purchasing, call our tire experts at **920-560-2430** -- they can help you understand the implications for your specific vehicle.
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