How tire size math works
A metric size such as 225/45R17 contains three pieces of information: 225 mm section width, a sidewall height equal to 45% of that width, and a 17-inch wheel diameter. Overall tire diameter is the wheel diameter plus two sidewalls.
Why diameter matters
A taller tire travels farther per revolution, which raises actual road speed at a given indicated speed and raises the vehicle by half the diameter change. A shorter tire does the opposite. Tire diameter also changes effective gearing slightly.
What the calculator cannot guarantee
Two tires with the same printed size can measure differently because of manufacturer tolerances, wheel width, load and inflation. Use the manufacturer’s published mounted diameter when exact clearance matters.
How much tire-size difference is acceptable?
There is no universal fitment limit. Small diameter changes are easier on speedometer calibration and systems that compare wheel speeds, but vehicle-specific requirements matter.