Why does tire size matter for a wheel swap?

Changing overall diameter by more than about 3% can throw off your speedometer, odometer, and gearing, since revolutions per mile change.

What units does this use?

Section width is entered in millimeters (standard on tire sidewalls) and wheel diameter in inches; all outputs are in inches for a typical U.S. audience.

Tire Size Calculator

Calculate overall tire diameter, sidewall height, and revolutions per mile from a tire size.

Format: Width / Aspect ratio R Wheel diameter (e.g. 225/45R17)

Section width (mm)

Aspect ratio (%)

Wheel diameter (in)

Overall diameter Enter your tire size above

Great for comparing two tire sizes before a wheel/tire swap to keep speedometer accuracy close to stock.

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How tire size numbers work

A tire size like 225/45R17 means: 225mm section width, a 45% aspect ratio (sidewall height as a percent of width), radial construction, and a 17-inch wheel diameter. This calculator converts that into overall tire diameter, sidewall height, circumference, and revolutions per mile.

Frequently asked questions

Why does tire size matter for a wheel swap?: Changing overall diameter by more than about 3% can throw off your speedometer, odometer, and gearing, since revolutions per mile change.
What units does this use?: Section width is entered in millimeters (standard on tire sidewalls) and wheel diameter in inches; all outputs are in inches for a typical U.S. audience.