Wheel width is the nominal bead-seat width. Backspacing uses the overall wheel width, estimated as nominal width + 1 inch unless you enter a measured width. Equal inner and outer flange allowances are assumed. Backspacing refers to the wheel itself; a spacer reduces its effective distance from the vehicle hub.

Metric tyre diameter = wheel diameter × 25.4 + 2 × section width × profile / 100. Inch format is overall diameter × section width – wheel diameter. Converting a format preserves dimensions; the result is not necessarily a tyre size sold by a manufacturer.

For race tyres, the width printed in the size may be tread width rather than section width. Use the manufacturer's section width and overall diameter under Measured dimensions. Tyre width varies with the measuring rim; this tool does not predict that change or tyre stretch.

Ride height is the nominal radius change, not a loaded measurement. The front view shows a schematic tyre silhouette using the specified section width and diameter; it does not predict the exact tread or sidewall contour.

References: WELD wheel technical information · Mickey Thompson tyre conversions