Offset in millimeters, backspacing in inches, and the question that actually matters: compared to what you run now, where does the new wheel sit?
Offset is where the mounting face sits against the wheel's centerline. Zero offset centers it. Positive offset moves the face outward, tucking the wheel in. Negative offset moves the face inward, pushing the wheel out, which is where the deep-dish truck look comes from.
Two wheels with the same offset but different widths put their inner lips in different places. Backspacing is the number that tells you whether the inner lip and tire will clear the control arm, tie rod, and inner fender, so serious fitment checks run on backspacing, not offset alone.
Pushing wheels far out changes the steering geometry and loads wheel bearings harder. A little poke is a look; a lot is a maintenance plan. If you go well beyond the factory position, budget for it.
About 4.53 inches. The math: half the overall width (9 + 1, divided by 2 = 5 inches), plus the offset in inches (-12 mm = -0.47 in), equals 4.53 inches of backspacing and 5.47 inches of front space.
Out. Negative offset moves the mounting face toward the inside of the wheel, so the whole wheel and tire sit further outboard. Positive offset does the opposite and tucks the wheel toward the suspension.
A quality hub-centric spacer effectively subtracts its thickness from the offset: a 1.5 inch spacer on a +25 wheel behaves like roughly -13 mm of added outward position. Cheap lug-centric spacers and over-stacking are where the horror stories come from. Whatever you run, the compare panel above shows the resulting position.
Pistons & Ink is a digital product studio based in Ocala, Florida, building web and mobile products for the automotive enthusiast community. We come from the custom car and truck world — lowriders, minitrucks, C10s, restomods — and we build tools we'd use ourselves.
This wheel offset calculator is one of 11 free tools in the Pistons & Ink Digital Toolbox, built for the aftermarket auto industry. If it helped you, the rest of the toolbox is right here.
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