Positive vs Negative Wheel Offset
Positive offset puts the hub face toward the street side of the wheel; negative puts it toward the brakes. See what each does to backspacing and poke.
Enter your numbers and press Calculate.
The difference
Les Schwab sums it up: with positive offset the hub mounting surface is in front of the centerline, toward the street side; with negative offset it is behind the centerline. Positive offset is the norm on front-wheel-drive cars and newer rear-drive vehicles, and deep-dish wheels are typically negative.
| Positive (+) | Zero (0) | Negative (−) | |
|---|---|---|---|
| Hub face | Street side of center | On the centerline | Brake side of center |
| Backspacing on a 9 in wheel | 5.98 in at +25 | 5.00 in | 4.02 in at −25 |
| Wheel sits | Farther in | Centered on the hub face | Farther out |
Going from positive to negative
On the same width, the outer lip moves out by the difference between the two offsets. A 9 in wheel going from +18 to −12 moves 30 mm (1.18 in) out at the lip, and the inner lip moves 30 mm away from the suspension.
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.
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
Does negative offset stick out?
It sits farther out than a positive-offset wheel of the same width. Whether it clears the fender depends on the vehicle and tire.
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.lesschwab.com/article/what-is-wheel-offset.html
- https://www.tirerack.com/wheels/tech/techpage.jsp?techid=101
- https://mickeythompsontires.com/tech-bulletins/backspacing-and-offset