Wheel Offset Chart: Backspacing by Width and ET
Last updated on September 25th, 2026
Use this wheel offset chart to find estimated backspacing from a wheel’s nominal width and offset (ET). Choose the width across the top, find the offset down the left, and read the value where they meet. Backspacing is shown in inches; offset is shown in millimeters.
Quick answer: For the same wheel width, a higher positive ET increases backspacing and moves the wheel inward. A lower ET moves it outward. The chart estimates the distance from the wheel’s mounting face to its rear rim lip; it does not identify a guaranteed fit for a vehicle.
Wheel Offset to Backspacing Chart
The chart covers 6.0–12.0-inch nominal wheel widths in half-inch steps and 25 selected offsets from ET−44 to ET+60. Its 325 results use the same stated calculation. These are reference combinations, not a list of wheel models or recommended offsets.
Chart assumption: The wheel’s overall lip-to-lip width is estimated as its nominal width plus 1 inch: approximately 0.5 inch of flange on each side. Actual rim geometry may differ. Use the exact manufacturer backspacing specification when available.
6.0–8.5-Inch Wheels
Estimated backspacing in inches. Column headings are nominal wheel widths.
| Offset (mm) | 6.0 in | 6.5 in | 7.0 in | 7.5 in | 8.0 in | 8.5 in |
|---|---|---|---|---|---|---|
| -44 | 1.77 | 2.02 | 2.27 | 2.52 | 2.77 | 3.02 |
| -38 | 2.00 | 2.25 | 2.50 | 2.75 | 3.00 | 3.25 |
| -30 | 2.32 | 2.57 | 2.82 | 3.07 | 3.32 | 3.57 |
| -25 | 2.52 | 2.77 | 3.02 | 3.27 | 3.52 | 3.77 |
| -24 | 2.56 | 2.81 | 3.06 | 3.31 | 3.56 | 3.81 |
| -20 | 2.71 | 2.96 | 3.21 | 3.46 | 3.71 | 3.96 |
| -18 | 2.79 | 3.04 | 3.29 | 3.54 | 3.79 | 4.04 |
| -12 | 3.03 | 3.28 | 3.53 | 3.78 | 4.03 | 4.28 |
| -6 | 3.26 | 3.51 | 3.76 | 4.01 | 4.26 | 4.51 |
| 0 | 3.50 | 3.75 | 4.00 | 4.25 | 4.50 | 4.75 |
| +6 | 3.74 | 3.99 | 4.24 | 4.49 | 4.74 | 4.99 |
| +10 | 3.89 | 4.14 | 4.39 | 4.64 | 4.89 | 5.14 |
| +12 | 3.97 | 4.22 | 4.47 | 4.72 | 4.97 | 5.22 |
| +15 | 4.09 | 4.34 | 4.59 | 4.84 | 5.09 | 5.34 |
| +18 | 4.21 | 4.46 | 4.71 | 4.96 | 5.21 | 5.46 |
| +20 | 4.29 | 4.54 | 4.79 | 5.04 | 5.29 | 5.54 |
| +25 | 4.48 | 4.73 | 4.98 | 5.23 | 5.48 | 5.73 |
| +30 | 4.68 | 4.93 | 5.18 | 5.43 | 5.68 | 5.93 |
| +35 | 4.88 | 5.13 | 5.38 | 5.63 | 5.88 | 6.13 |
| +38 | 5.00 | 5.25 | 5.50 | 5.75 | 6.00 | 6.25 |
| +40 | 5.07 | 5.32 | 5.57 | 5.82 | 6.07 | 6.32 |
| +45 | 5.27 | 5.52 | 5.77 | 6.02 | 6.27 | 6.52 |
| +50 | 5.47 | 5.72 | 5.97 | 6.22 | 6.47 | 6.72 |
| +55 | 5.67 | 5.92 | 6.17 | 6.42 | 6.67 | 6.92 |
| +60 | 5.86 | 6.11 | 6.36 | 6.61 | 6.86 | 7.11 |
9.0–12.0-Inch Wheels
Estimated backspacing in inches. Column headings are nominal wheel widths.
| Offset (mm) | 9.0 in | 9.5 in | 10.0 in | 10.5 in | 11.0 in | 11.5 in | 12.0 in |
|---|---|---|---|---|---|---|---|
| -44 | 3.27 | 3.52 | 3.77 | 4.02 | 4.27 | 4.52 | 4.77 |
| -38 | 3.50 | 3.75 | 4.00 | 4.25 | 4.50 | 4.75 | 5.00 |
| -30 | 3.82 | 4.07 | 4.32 | 4.57 | 4.82 | 5.07 | 5.32 |
| -25 | 4.02 | 4.27 | 4.52 | 4.77 | 5.02 | 5.27 | 5.52 |
| -24 | 4.06 | 4.31 | 4.56 | 4.81 | 5.06 | 5.31 | 5.56 |
| -20 | 4.21 | 4.46 | 4.71 | 4.96 | 5.21 | 5.46 | 5.71 |
| -18 | 4.29 | 4.54 | 4.79 | 5.04 | 5.29 | 5.54 | 5.79 |
| -12 | 4.53 | 4.78 | 5.03 | 5.28 | 5.53 | 5.78 | 6.03 |
| -6 | 4.76 | 5.01 | 5.26 | 5.51 | 5.76 | 6.01 | 6.26 |
| 0 | 5.00 | 5.25 | 5.50 | 5.75 | 6.00 | 6.25 | 6.50 |
| +6 | 5.24 | 5.49 | 5.74 | 5.99 | 6.24 | 6.49 | 6.74 |
| +10 | 5.39 | 5.64 | 5.89 | 6.14 | 6.39 | 6.64 | 6.89 |
| +12 | 5.47 | 5.72 | 5.97 | 6.22 | 6.47 | 6.72 | 6.97 |
| +15 | 5.59 | 5.84 | 6.09 | 6.34 | 6.59 | 6.84 | 7.09 |
| +18 | 5.71 | 5.96 | 6.21 | 6.46 | 6.71 | 6.96 | 7.21 |
| +20 | 5.79 | 6.04 | 6.29 | 6.54 | 6.79 | 7.04 | 7.29 |
| +25 | 5.98 | 6.23 | 6.48 | 6.73 | 6.98 | 7.23 | 7.48 |
| +30 | 6.18 | 6.43 | 6.68 | 6.93 | 7.18 | 7.43 | 7.68 |
| +35 | 6.38 | 6.63 | 6.88 | 7.13 | 7.38 | 7.63 | 7.88 |
| +38 | 6.50 | 6.75 | 7.00 | 7.25 | 7.50 | 7.75 | 8.00 |
| +40 | 6.57 | 6.82 | 7.07 | 7.32 | 7.57 | 7.82 | 8.07 |
| +45 | 6.77 | 7.02 | 7.27 | 7.52 | 7.77 | 8.02 | 8.27 |
| +50 | 6.97 | 7.22 | 7.47 | 7.72 | 7.97 | 8.22 | 8.47 |
| +55 | 7.17 | 7.42 | 7.67 | 7.92 | 8.17 | 8.42 | 8.67 |
| +60 | 7.36 | 7.61 | 7.86 | 8.11 | 8.36 | 8.61 | 8.86 |
How to Read a Cell
Suppose your wheel is marked 18 × 8.5 ET35. The 18 is its diameter in inches, 8.5 is its nominal width in inches, and ET35 is a positive 35 mm offset. Find the 8.5 in column in the first table and the +35 mm row. Their intersection is 6.13 inches of estimated backspacing.
Choose the marked 8.5-inch width, not the tire width or an estimated 9.5-inch overall wheel width. The chart already includes its 1-inch total flange allowance. Wheel diameter does not enter the backspacing formula.
If your offset or width is missing, use the formula below with the actual number instead of selecting the nearest chart cell.
What Positive, Zero, and Negative Offset Mean
Offset measures the distance from the wheel’s centerline to its hub-mounting face. Positive ET puts the mounting face toward the outside of the wheel; negative ET puts it toward the inside. At ET0, the mounting face and rim centerline align.
For a fuller explanation of offset markings, see our wheel offset guide.
Once mounted against the same vehicle hub, a lower offset moves the wheel outward. Compare ET45 with ET35 on two otherwise equivalent wheels: ET35 sits 10 mm farther outward, even though both offsets are positive. Zero ET does not mean zero backspacing or a wheel that sits flush with a fender.
Wheel Offset Change Chart: How Far Will It Move?
When the two wheels have the same width and rim geometry, calculate their change in position as:
Outward movement (mm) = Original ET − New ET
A positive answer means outward movement; a negative answer means inward movement. With a fixed inner reference surface, moving outward increases inner rim clearance by the same amount and reduces the outer gap by that amount. These are rim-position changes, not final tire or fender clearances.
| Original ET | New ET | Wheel movement | Inner rim clearance change |
|---|---|---|---|
| +45 mm | +35 mm | 10 mm outward | 10 mm more |
| +35 mm | +45 mm | 10 mm inward | 10 mm less |
| +35 mm | +20 mm | 15 mm outward | 15 mm more |
| +20 mm | 0 mm | 20 mm outward | 20 mm more |
| 0 mm | −12 mm | 12 mm outward | 12 mm more |
| 0 mm | +12 mm | 12 mm inward | 12 mm less |
| −12 mm | −24 mm | 12 mm outward | 12 mm more |
| −24 mm | −12 mm | 12 mm inward | 12 mm less |
For an 18 × 8 ET45 wheel changed to 18 × 8 ET35, the calculation is 45 − 35 = 10 mm outward. Both rim edges move 10 mm outward, assuming matching rim shapes. That does not mean the tire will stick out 10 mm past the fender.
Keep the negative signs in the calculation. Moving from ET−12 to ET−24 gives −12 − (−24) = +12 mm, or 12 mm outward.
Wheel Width and Offset Change Chart
When wheel width also changes, ET alone cannot describe either rim edge. For equal flange dimensions, each additional 1 inch of width extends the wheel by 12.7 mm on each side before accounting for the offset change.
The following examples compare the same vehicle mounting plane, with no change in spacers. A positive inner-clearance change means more lateral space at the inner rim edge. Tire sidewall and brake clearance need separate checks.
| Original wheel | New wheel | Outer rim change | Inner rim clearance change |
|---|---|---|---|
| 8 in ET+35 | 9 in ET+35 | 12.7 mm farther out | 12.7 mm less |
| 8 in ET+45 | 9 in ET+35 | 22.7 mm farther out | 2.7 mm less |
| 8 in ET+35 | 9 in ET+45 | 2.7 mm farther out | 22.7 mm less |
| 9 in ET+35 | 8 in ET+35 | 12.7 mm farther in | 12.7 mm more |
| 8.5 in ET+40 | 9.5 in ET+30 | 22.7 mm farther out | 2.7 mm less |
| 9 in ET0 | 10 in ET−12 | 24.7 mm farther out | 0.7 mm less |
Use the two calculations below. Enter wheel widths in inches and ET values in millimeters:
Half-width change (mm) = (New width − Original width) × 25.4 ÷ 2
Outward shift from ET (mm) = Original ET − New ET
Outer rim change (mm) = Half-width change + Outward shift from ET
Inner rim clearance gain (mm) = Outward shift from ET − Half-width change
For example, change from 18 × 8 ET45 to 18 × 9 ET35. An extra inch adds 12.7 mm on each side; lowering ET by 10 moves the centerline 10 mm outward. The outer edge moves 12.7 + 10 = 22.7 mm outward, while inner clearance changes by 10 − 12.7 = −2.7 mm: 2.7 mm less. A lower ET therefore does not necessarily gain inner clearance when the wheel is wider.
At the same ET, changing from 18 × 8 ET35 to 18 × 9 ET35 moves the outer edge 12.7 mm out and leaves 12.7 mm less inner clearance. If the new 9-inch wheel instead has ET45, its outer edge moves 2.7 mm out, but inner clearance falls by 22.7 mm. Looking only at how far the wheel appears to stick out would miss that inner change.
These formulas compare rim edges with matching flange extensions. A mounted tire can be wider than the rim, and its section width can change with approved rim width. Check the dimensions for the exact tire model; Tire Rack explains how rim width affects tire specifications.
Offset to Backspacing Conversion
The wheel’s stamped nominal width measures between the inside flange faces where the tire beads seat. Overall width spans the outside of both rim lips. Backspacing is measured from the rear rim lip to the mounting face; these reference points explain why stamped width alone cannot be halved to obtain backspacing.
Calculate Backspacing From Offset
Using this chart’s estimated 1-inch total flange allowance:
Backspacing (inches) = (Nominal wheel width + 1) ÷ 2 + ET ÷ 25.4
For an 8.5-inch ET35 wheel: (8.5 + 1) ÷ 2 + 35 ÷ 25.4 = 6.12795 inches, which rounds to 6.13 inches in the chart. For negative ET, keep the minus sign when adding the ET term.
Calculate Offset From Backspacing
Offset (mm) = [Backspacing (inches) − (Nominal width + 1) ÷ 2] × 25.4
For an 8-inch wheel with 5.50 inches of backspacing, the estimated offset is [5.50 − (8 + 1) ÷ 2] × 25.4 = +25.4 mm. For a 9-inch wheel with 4.50 inches of backspacing, it is [4.50 − (9 + 1) ÷ 2] × 25.4 = −12.7 mm. These calculated results need not match a rounded ET offered in a catalog.
If you have a reliable measured overall width and the flanges extend equally on both sides, replace “nominal width + 1” with that overall width. Do not add another inch. Where the flange shape is unusual or asymmetric, use the manufacturer’s dimensions rather than assuming half the overall width locates the rim centerline.
A measurement must use the rear rim-lip plane and flat hub-mounting face for backspacing—not the tire sidewall or decorative wheel face. If the wheel’s ET is unknown, identify its part number and manufacturer specification first. Otherwise, measure a bare wheel with a straightedge across the rear lip; subtract straightedge thickness if you measure to its top surface.
Wheel Spacers and Effective Offset
A spacer moves the installed wheel outward without changing the ET stamped on the bare wheel. For a spacer fitted at one wheel:
Effective ET (mm) = Stamped wheel ET − Spacer thickness (mm)
An ET45 wheel with a 15 mm spacer has ET30 effective offset and moves 15 mm outward relative to the same wheel without a spacer. Its bare-wheel backspacing remains the value calculated from ET45, not ET30. If you replace a 5 mm spacer with a 15 mm spacer on that wheel, the additional outward movement is 10 mm.
Effective ET helps compare installed positions; it does not establish whether the spacer, mounting hardware or wheel is suitable for the vehicle. Follow the instructions for the exact spacer system and wheel. H&R distinguishes spacer mounting systems.
Can the Chart Confirm Wheel Fitment?
No. It estimates backspacing and rim position. Before buying, compare the proposed setup with the exact vehicle year, trim and brake package, then check:
- Wheel diameter, width, ET, bolt pattern, center bore, mounting hardware and wheel load rating.
- The exact tire’s approved rim-width range, load capacity, section width and overall diameter.
- Inner and outer clearance for both the wheel and tire, including steering and suspension travel.
- Barrel and spoke clearance around the brakes; matching wheel diameter and ET alone cannot confirm it.
A bare-wheel test fit before mounting the tire can resolve uncertain brake or hub clearance. The completed wheel-and-tire package also needs a vehicle check. RAYS’ wheel installation guidance calls for compatibility and post-installation contact checks. There is no universal “safe ET range” that applies to every vehicle.
Wheel Offset Chart FAQs
Is ET35 or ET45 farther out?
On otherwise equivalent wheels of the same width, ET35 sits 10 mm farther out than ET45. Different widths or spacers require the separate calculations above.
Is zero offset the same as zero backspacing?
No. ET0 puts the mounting face at the rim centerline. An 8.5-inch ET0 wheel has about 4.75 inches of backspacing under this chart’s flange assumption.
Does diameter change a chart value?
No. Diameter is absent from the formula. An 18 × 8 and a 20 × 8 wheel at the same ET have equal estimated backspacing if their flange geometry matches, although their brake and tire fitment can differ.
Why is my measured backspacing different?
The chart assumes 0.5 inch per flange and rounds displayed results to 0.01 inch. Actual flange dimensions, measurement reference points and straightedge thickness can cause differences. Check the manufacturer’s stated dimension when available.
Does negative offset always put the tire past the fender?
No. Negative ET positions the wheel centerline outward of the hub mounting plane, but fender location, wheel width and tire dimensions determine whether anything protrudes.
Chart Formula, Rounding, and Verification
All 325 chart cells were computed as (nominal width + 1) ÷ 2 + ET ÷ 25.4 and displayed to the nearest 0.01 inch. The conversion 1 inch = exactly 25.4 mm comes from NIST. The 1-inch flange allowance is an estimate used in a common conversion method illustrated by Curva Concepts, not a measured property of every wheel.
Every displayed cell was checked against the stated formula. The reverse offset calculation using rounded cells differed from the source ET by at most 0.124 mm across this chart; the theoretical rounding-only bound is 0.127 mm. Rounding does not bound error from real flange dimensions or physical measurement.
These checks establish the chart’s arithmetic, not the existence of every width/ET combination or fitment approval. Use a manufacturer’s wheel specification and a physical fitment check when choosing a wheel-and-tire package.
