Compare an original tire size against a new one to see exactly how the swap changes your car. Enter both sizes using width, aspect ratio, and wheel diameter, and this calculator shows the overall diameter of each tire, the percentage difference, and how far off your speedometer will read once the new size is fitted. A larger diameter makes the speedometer read slower than you are actually going, while a smaller one reads faster, and even a small change can push you outside the safe one to three percent window that manufacturers target. This is the tool to use before fitting a plus size wheel, going to a taller off road tire, or switching to winter rubber. It also flags whether the change is within a generally acceptable range. All figures are computed locally in your browser.
It reports the difference in overall diameter and sidewall height and how the new size changes your speedometer reading.
A larger diameter makes the true speed higher than the speedometer shows, while a smaller diameter makes it lower.
Yes. It helps check that a plus size wheel and tire keep a similar overall diameter to avoid clearance and accuracy issues.
Compare an original tire size against a new one to see exactly how the swap changes your car. Enter both sizes using width, aspect ratio, and wheel diameter, and this calculator shows the overall diameter of each tire, the percentage difference, and how far off your speedometer will read once the new size is fitted.
Yes. Tire Size Comparison Calculator is completely free, with no sign-up and no usage limits.
Yes. Tire Size Comparison Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Tire Size Comparison Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.