3 Inch Backspacing: What Offset Is It?
It depends on the wheel width. 3 inches of backspacing works out to −50.8 mm on a 9-inch wheel and −63.5 mm on a 10-inch wheel.
Enter your numbers and press Calculate.
3 in backspacing by wheel width
| Width | Offset | Rounded |
|---|---|---|
| 7 in | −25.4 mm | −25 mm |
| 7.5 in | −31.8 mm | −32 mm |
| 8 in | −38.1 mm | −38 mm |
| 8.5 in | −44.4 mm | −44 mm |
| 9 in | −50.8 mm | −51 mm |
| 9.5 in | −57.1 mm | −57 mm |
| 10 in | −63.5 mm | −64 mm |
| 11 in | −76.2 mm | −76 mm |
| 12 in | −88.9 mm | −89 mm |
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.
Working it out
Offset = (3 − (width + 1) ÷ 2) × 25.4
For a 9-inch wheel: (9 + 1) ÷ 2 = 5; 3 − 5 = -2.00 in; × 25.4 = −50.8 mm.
Front spacing with 3 in of backspacing
Front spacing is how far the outer lip reaches past the hub face: overall width minus backspacing. With backspacing fixed at 3 inches, every extra inch of width goes entirely to the outside.
| Stated width | Overall width | Front spacing | Offset |
|---|---|---|---|
| 6 in | 7.0 in | 4.00 in | −12.7 mm |
| 7 in | 8.0 in | 5.00 in | −25.4 mm |
| 7.5 in | 8.5 in | 5.50 in | −31.8 mm |
| 8 in | 9.0 in | 6.00 in | −38.1 mm |
| 8.5 in | 9.5 in | 6.50 in | −44.4 mm |
| 9 in | 10.0 in | 7.00 in | −50.8 mm |
| 9.5 in | 10.5 in | 7.50 in | −57.1 mm |
| 10 in | 11.0 in | 8.00 in | −63.5 mm |
| 11 in | 12.0 in | 9.00 in | −76.2 mm |
| 12 in | 13.0 in | 10.00 in | −88.9 mm |
Next to 3 inches
Each half inch of backspacing is 12.7 mm of offset on the same width.
| Backspacing | Offset change vs 3 in |
|---|---|
| 2 in | −25.4 mm |
| 2.5 in | −12.7 mm |
| 3.5 in | +12.7 mm |
| 4 in | +25.4 mm |
Measuring backspacing yourself
- Lay the wheel face down on a flat floor.
- Rest a straightedge across the inner lip.
- Measure straight down to the hub mounting pad.
That reading is the backspacing. Measure in two or three places around the pad and use the average if the readings differ.
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 3 backspacing positive or negative offset?
On widths narrower than 5 inches it is positive; wider than that it is negative.
How much front spacing does a 9 inch wheel with 3 backspacing have?
7.00 inches (10 in overall − 3 in).
What width wheel is zero offset at 3 in backspacing?
5 inches, because zero offset means backspacing equals half the overall width.
Related calculators
Sources
- https://mickeythompsontires.com/tech-bulletins/backspacing-and-offset
- https://speedwaymotors.com/the-toolbox/wheel-offset-vs-backspacing-explained/30059