Formula Used
The calculator treats offset as the distance from wheel centerline to hub mounting face. Positive offset moves the wheel inward. A spacer lowers the effective offset.
wheel_width_mm = wheel_width_in × 25.4
effective_new_offset = new_offset - spacer
inner_lip = (wheel_width_mm ÷ 2) + offset
outer_lip = (wheel_width_mm ÷ 2) - offset
inner_change = new_inner_lip - current_inner_lip
outer_change = new_outer_lip - current_outer_lip
track_center_change = 2 × (current_offset - effective_new_offset)
backspace_in = (wheel_width_in ÷ 2) + (offset_mm ÷ 25.4)
Positive inner change means the new setup moves closer to suspension. Positive outer change means the new setup pokes farther outward.
Wheel Offset Planning by Car
Wheel offset affects how a wheel sits on a car. It changes stance, steering feel, bearing load, and body clearance. A small number can make a large visual change. That is why a car based offset check matters before buying wheels. This calculator compares your current setup with a new setup. It uses wheel width, offset, spacer thickness, and tire section width. It then shows inner clearance change and outer poke change.
Why Offset Matters
Offset is measured in millimeters. A higher positive offset pulls the wheel inward. A lower offset pushes it outward. Wider wheels also change both sides of the wheel. Half of the added width moves inward. The other half moves outward, unless offset changes too. This is why width and offset must be checked together.
Clearance and Poke
Inner clearance protects the strut, control arm, brake lines, and liner. Outer clearance protects the fender and bumper edge. Tire width can matter more than wheel width. A square tire may sit wide. A stretched tire may sit narrower. Real tire shape also depends on brand, rim width, pressure, and load.
Advanced Fitment Checks
The tool also estimates centerline shift. This helps you see track change. Large shifts can affect scrub radius. They may also increase steering kickback. Spacers reduce effective offset. They can help clear brakes, but they need proper hub support and fastener engagement. Always check lug seat type and center bore.
Best Practice
Use factory wheel data as your baseline. Measure actual clearance on the car. Check both front and rear axles. Lowered cars need extra care. Camber, ride height, fender shape, and suspension travel all change real clearance. Use this result as a planning guide. Then test fit before driving.
FAQs
What is wheel offset?
Wheel offset is the distance from the wheel centerline to the mounting face. Positive offset places the mounting face outward, which pulls the wheel inward.
What does lower offset do?
Lower offset usually pushes the wheel outward. It can improve stance, but it may reduce fender clearance and change steering feel.
Does wheel width affect poke?
Yes. A wider wheel adds width to both sides. Offset decides how much of that extra width moves inward or outward.
Should I include tire width?
Yes, when possible. Tire section width helps estimate sidewall clearance. It is useful because tires may extend beyond the wheel lip.
How does a spacer affect offset?
A spacer reduces effective offset. For example, a 5 mm spacer changes ET40 into effective ET35.
Is positive outer change bad?
Not always. Positive outer change means more poke. It is only a problem when it exceeds fender clearance or legal limits.
What is backspacing?
Backspacing is the distance from the mounting face to the inner wheel lip. More backspacing usually means the wheel sits closer to suspension parts.
Can this guarantee fitment?
No. It gives a strong estimate. Real fitment also depends on brakes, hub bore, tire shape, camber, ride height, and suspension travel.