Calculator
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The tool works out each tyre's overall diameter from its width, aspect ratio, and rim size, then reports the percentage difference. A large gap changes your effective gearing and speedometer reading.
Fitment guides generally keep the overall diameter within a few percent of stock so the speedometer stays accurate and clearances are safe. This compares diameters only — it does not check width clearance or load rating.
That is the promise behind every tool here. Files are read in your browser tab, processed there, and discarded when you close it — never uploaded to our servers.
