What Is Wheel Offset?
Wheel offset is the distance in millimeters from the wheel's hub mounting surface to its centerline. Here is what positive, zero and negative offset mean, and how offset moves the wheel in or out.
Enter your numbers and press Calculate.
The definition
Tire Rack defines offset as the distance from a wheel's hub mounting surface to the centerline of the wheel, measured in millimeters. It comes in three kinds:
- Zero offset: the hub mounting surface is even with the centerline.
- Positive offset: the hub mounting surface sits toward the street side of the centerline. Les Schwab notes that most wheels on front-wheel-drive cars and newer rear-drive vehicles are positive.
- Negative offset: the hub mounting surface sits toward the brake side. Les Schwab says deep-dish wheels are typically negative.
SimpleTire notes the number is often stamped on the wheel as ET followed by the value, so ET35 is +35 mm.
What changing offset does
The hub face is bolted to the car, so it never moves. Changing offset moves the rest of the wheel around it. On the same width wheel, every millimeter less offset pushes both lips one millimeter farther out; every millimeter more pulls them in. A wider wheel adds half its extra width on each side.
Backspacing (in) = (width + 1) ÷ 2 + offset ÷ 25.4
Overall wheel width is the stated width plus about 1 inch, because each bead flange adds about half an inch. Mickey Thompson, Speedway Motors and Discount Tire all use that convention, and so does every calculator on this site.
Backspacing by width and offset
| Width | −44 mm | −24 mm | −12 mm | 0 mm | +15 mm | +25 mm | +35 mm | +45 mm |
|---|---|---|---|---|---|---|---|---|
| 6 in | 1.77 | 2.56 | 3.03 | 3.50 | 4.09 | 4.48 | 4.88 | 5.27 |
| 6.5 in | 2.02 | 2.81 | 3.28 | 3.75 | 4.34 | 4.73 | 5.13 | 5.52 |
| 7 in | 2.27 | 3.06 | 3.53 | 4.00 | 4.59 | 4.98 | 5.38 | 5.77 |
| 7.5 in | 2.52 | 3.31 | 3.78 | 4.25 | 4.84 | 5.23 | 5.63 | 6.02 |
| 8 in | 2.77 | 3.56 | 4.03 | 4.50 | 5.09 | 5.48 | 5.88 | 6.27 |
| 8.5 in | 3.02 | 3.81 | 4.28 | 4.75 | 5.34 | 5.73 | 6.13 | 6.52 |
| 9 in | 3.27 | 4.06 | 4.53 | 5.00 | 5.59 | 5.98 | 6.38 | 6.77 |
| 9.5 in | 3.52 | 4.31 | 4.78 | 5.25 | 5.84 | 6.23 | 6.63 | 7.02 |
| 10 in | 3.77 | 4.56 | 5.03 | 5.50 | 6.09 | 6.48 | 6.88 | 7.27 |
| 11 in | 4.27 | 5.06 | 5.53 | 6.00 | 6.59 | 6.98 | 7.38 | 7.77 |
| 12 in | 4.77 | 5.56 | 6.03 | 6.50 | 7.09 | 7.48 | 7.88 | 8.27 |
Backspacing in inches = (width + 1) ÷ 2 + offset ÷ 25.4.
Common wheel specs, worked out
| Wheel | Backspacing | Front spacing |
|---|---|---|
| 7.5 × +45 | 6.02 in | 2.48 in |
| 8 × +35 | 5.88 in | 3.12 in |
| 8.5 × +35 | 6.13 in | 3.37 in |
| 9 × +18 | 5.71 in | 4.29 in |
| 9 × 0 | 5.00 in | 5.00 in |
| 10 × −24 | 4.56 in | 6.44 in |
| 12 × −44 | 4.77 in | 8.23 in |
Overall width = stated width + 1 in.
Common mistakes
- Using the stated width as the overall width. A 9-inch wheel measures about 10 inches lip to lip because each bead flange adds roughly half an inch. Skip that inch and every backspacing figure is half an inch off.
- Dropping the minus sign. −12 and +12 are 24 mm apart. A wheel stamped ET-12 or −12 is negative.
- Comparing offsets across different widths. A wider wheel adds half its extra width on each side, so a 10-inch wheel at +25 can still stick out further than a 9-inch wheel at +18.
- Forgetting the tire. A wider tire grows half its extra width on each side of the wheel, and sidewall bulge varies between brands of the same size.
Check clearance before you buy
Offset and width tell you where the wheel's lips end up; they do not tell you what is in the way. Before ordering, measure your current setup:
- Inner clearance. With the wheels straight, measure from the inner lip of the current wheel to the nearest suspension part: strut body, spring perch, upper control arm or sway bar link. If the new wheel's inner lip moves in by more than that gap, it will hit.
- Brake clearance. Big calipers sit inside the barrel. The spoke face, not just the lip, has to clear them, which is why a wheel's spoke design matters as much as its offset.
- Outer clearance. Hang a plumb line or hold a level against the fender lip and measure in to the tire's sidewall. A new wheel that moves out more than that gap will stick past the fender.
- Steering and suspension travel. Turn to full lock and check the fender liner, then remember the suspension compresses over bumps. Static clearance is the best case.
Enter both wheels in the calculator above: the outer-lip number is the extra space you need at the fender, and the inner-lip number is the extra space you need at the suspension.
Common questions
Is a higher offset better?
No. The right offset is the one that clears the brakes and suspension on the inside and the fender on the outside. Higher offset tucks the wheel in; lower offset pushes it out.
What does +35 offset mean?
The hub mounting surface is 35 mm (1.38 in) toward the street side of the wheel's centerline.
Does offset change with tire size?
No. Offset belongs to the wheel. A different tire changes how wide the assembly is, not where the hub face sits.
What is front spacing?
The distance from the hub face to the outer lip: overall width minus backspacing.
Sources
- https://www.tirerack.com/wheels/tech/techpage.jsp?techid=101
- https://www.lesschwab.com/article/what-is-wheel-offset.html
- https://simpletire.com/learn/tire-maintenance-safety/wheel-offsets
- https://mickeythompsontires.com/tech-bulletins/backspacing-and-offset
- https://speedwaymotors.com/the-toolbox/wheel-offset-vs-backspacing-explained/30059