Free Wheel Offset calculator with clear step-by-step results.
Offset is measured from the mounting face to the wheel's centreline, so changing both width and offset moves the inner and outer edges independently. The inner figure is what determines strut and suspension clearance; the outer figure determines arch clearance and whether the tyre protrudes.
Inner edge position
Inner = wheel width / 2 + offset
Outer edge position
Outer = wheel width / 2 - offset
Wheel and tyre fitment affects steering geometry, bearing loads and tyre containment within the bodywork. Non-compliant fitment can breach construction and use regulations and invalidate insurance.
For the same width, yes - reducing offset by 10 mm moves the wheel 10 mm outward. But widening the wheel moves both edges outward by half the width increase as well.
At least 5 mm static to the strut and more at full lock and full suspension travel. Inner clearance is where most fitment failures actually occur.