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Fileraz
Tools
Fileraz
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Car & Bike Calculator
Driver-entered figures, reviewed October 2026 — no OBD, live prices, maps, or RTO data. Confirm fitment and costs with charts and vendors.
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Overall diameter is rim × 25.4 + 2 × width × aspect ÷ 100 in millimetres: a 195/65R15 works out to 634.5 mm and the same tyre on a 16-inch rim to 659.9 mm — a +4.00% gap that makes the speedometer read about 4% low. The page shows both diameters beside the percent so the sizes stay concrete, not abstract.
Read width, aspect, and rim off both sidewalls (195/65R15 means 195 mm wide, 65% sidewall, 15-inch rim) and enter all six figures — aspect alone means nothing without its width. Fitment guides generally keep the gap within ~3% so gearing, clearances, and the speedometer stay sane; treat anything larger as a decision needing a fitment chart, not arithmetic.
It does not check width clearance against arches, verify load or speed ratings, or approve the fitment — diameters and percent only, with the vendor's chart as the final word before buying.
Diameters only — clearance and load ratings need fitment charts.
Commonly within about 3% of the original, but follow your vehicle's fitment guidance and check clearances.
Yes. A larger diameter makes the speedometer read low, and a smaller one makes it read high, in proportion to the change.
Because sidewall height is width × aspect ÷ 100 — the aspect percent alone has no millimetres in it. Same aspect on different widths gives different diameters.
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