Positive, zero and negative offset
Offset measures the mounting face relative to the wheel centerline. Positive offset places the mounting face toward the outer face of the wheel, which generally pulls the wheel inward. Negative offset pushes it outward.
Why width and offset must be considered together
Adding an inch of wheel width adds roughly half an inch to each side before any offset change is considered. Lowering offset then moves the entire wheel farther outward. That combination can create both more inner clearance and substantially more outer poke.
What backspacing means
Backspacing measures from the hub mounting face to the wheel’s inner edge. It is usually expressed in inches. Because wheel width is normally specified at the bead seats while physical backspacing can reference the outer lip, manufacturer measurements are best when clearances are tight.
Common fitment traps
A wheel can clear the fender while contacting a strut, control arm or brake caliper. A setup that clears while parked can also rub under steering lock, suspension compression or body roll.