Tyre Size Calculator

Compare two tyre sizes side by side. See overall diameter, sidewall, circumference, revs/km, speedo error in km/h and ride-height change. Built to AU ADR 18/03 tolerances. Then have an AutoCraze fitment expert match the right tyres to your car.

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Original tyre

Width (mm)

Profile (%)

Rim (in)

New tyre

Width (mm)

Profile (%)

Rim (in)

Measurement

Original

New

Difference

Overall diameter

Sidewall height

Section width

Circumference

Revolutions per km

Speedo reads 100 km/h, actual

100.0 km/h

Ride-height change

0 mm

Calculating... Set values above and press Calculate.

Get a free fitment quote on these tyres

An AutoCraze expert will match the right tyres to your car, confirm fitment, and put together pricing — including a finance plan if you want one. No obligation. We usually reply within an hour during showroom hours.

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How tyre sizes work

235 = section width (mm). 45 = aspect ratio (sidewall as % of width). R18 = radial construction on an 18" rim.

Overall diameter = rim diameter + (2 × sidewall height). In Australia, your speedo must read at or above true speed (ADR 18/03). Stay within ±3% of stock to be safe.

Tyre Size Calculator — Compare Sizes, Diameter & Speedo Impact