How much difference is safe?

Stay within roughly ±3 % of the original overall diameter — beyond that, ABS, traction control and gearing notice it.

Does rim width matter here?

No, this calculator only models the overall diameter; rim width changes how the tyre sidewall is supported.

Tyre & wheel calculators

Enter width, sidewall ratio and rim size to get the total wheel diameter and the difference from stock.

diameter = rim × 25.4 + 2 × (width × ratio/100)

A difference of up to about 3 % is usually accepted by inspection bodies and keeps the speedometer error negligible.
A larger diameter raises the ride height and effective gearing; a smaller one does the opposite and can make the speedometer read high.

Tyre width(mm)

Sidewall ratio(%)

Rim diameter(in)

Reference diameter(mm)

634.3 mm

Δ -7.5 %

Formula: diameter = rim × 25.4 + 2 × (width × ratio/100)
Example: Width: 225 mm Ratio: 45 % Rim: 17 in Reference: 686 mm Diameter: 634.3 mm Difference: -7.6 %

Example

Width: 225 mm
Ratio: 45 %
Rim: 17 in
Reference: 686 mm
Diameter: 634.3 mm
Difference: -7.6 %

How much difference is safe?: Stay within roughly ±3 % of the original overall diameter — beyond that, ABS, traction control and gearing notice it.
Does rim width matter here?: No, this calculator only models the overall diameter; rim width changes how the tyre sidewall is supported.

Copies: 5,640 · Views: 14,020 · Updated: Sep 18, 2026

P0300

The ECU detected misfires on several cylinders without a single identifiable source.

errors