For planning purposes only. Actual costs may vary. Not financial advice.
Calculator tool
How this calculator works
Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.
What tire-size math uses
The calculator derives sidewall height from width and aspect ratio, then adds two sidewalls to the rim diameter:
Because the speedometer is tied to wheel rotations, a tire with larger circumference travels farther per revolution. The tool compares original and new circumference to estimate the speedometer percentage error.
Why a small percentage matters
If the new tire is larger, the vehicle usually travels faster than the speedometer suggests; if it is smaller, the speedometer tends to read faster than true road speed. The calculator flags changes beyond 3% because larger departures are a common practical threshold for closer review.
Use this page to compare fitment options, then check clearance, load rating, wheel width compatibility, and vehicle guidance before installing a new size.
Frequently asked questions
What do the tire numbers mean?
In a size such as 225/45R17, 225 is width in millimeters, 45 is sidewall height as a percent of width, and 17 is rim diameter in inches.
Why does tire diameter affect the speedometer?
A different circumference changes how far the vehicle travels per wheel revolution, while the speedometer calibration still assumes the original tire size.
Does the calculator confirm the tire will fit?
No. It compares dimensions and modeled speedometer effect only. You still need to verify suspension clearance, wheel width, offset, and manufacturer guidance.
Why does the page warn above 3%?
The implemented tool uses 3% as a practical review threshold so larger diameter changes are easier to spot before installation.
