Manual

Tire Size Calculator Manual

Compare nominal dimensions of two supported metric radial passenger-tire sizes. Do not treat this calculation as fitment approval.

1. Enter your current size

Type the code from the sidewall such as 205/55R16. The number before the slash is section width in millimeters. The number after it is aspect ratio; the number following R is rim diameter in inches.

2. Enter a new tire size

Use a second supported metric radial size, such as 225/45R17. This is a comparison example, not a recommendation for a vehicle. Unsupported sizes are rejected.

3. Choose a speed comparison

Enter the indicated speed and select mph or km/h. The result estimates the effective speed under a simplified original-diameter calibration assumption. It is not a measured road speed.

4. Review the comparison

Select Compare sizes. Review nominal section width, sidewall height, diameter, circumference, estimated revolutions per mile and signed diameter percentage difference. Editing any input clears the old result and disables export until you compare again.

5. Copy, download or print

Copy summary saves text to your clipboard if the browser permits it. Download CSV saves a spreadsheet-ready report. Print / Save PDF opens the browser print dialog. The same nominal calculation drives every output.

Limits and safety

Real tire dimensions and rolling circumference vary. You must verify wheel and vehicle compatibility, clearance, load index and speed rating with manufacturer specifications and an appropriate professional before installation. A percentage difference threshold does not certify safety or fitment.