Effective offset
ET+35.0
Offset minus spacerThis describes a mounting-position change, not approval of a spacer installation.
Wheel Spacer Calculator
Enter stamped offset and added spacer thickness to calculate effective ET, outward movement and the equal-both-sides track implication.
Result updated. A 10.0 mm spacer changes ET+45.0 to effective ET+35.0. The same wheel moves outward by 10.0 mm.
Result
A 10.0 mm spacer changes ET+45.0 to effective ET+35.0. The same wheel moves outward by 10.0 mm.
Outward movement
10.0 mm
Toward the fenderInner relative clearance increases by this amount for the same wheel.
Symmetric axle track change
+20.0 mm
Wider centreline trackOnly when identical spacer thickness is added on both sides.
Details
- Inner clearance change
- +10.0 mm
Results use nominal geometry and the stated conventions. They are dimensional answers, not a fitment, safety or legality check.
How does a spacer change offset?
A spacer separates the wheel mounting face from the hub. For an otherwise unchanged wheel, that moves the entire wheel outward by the spacer thickness. Both nominal wheel edges move together, so relative suspension-side space increases by the same amount while the outer edge moves toward the fender.
Effective offset = stamped offset − added spacer thickness. A positive stamped ET can become a smaller positive, zero or negative effective value. Keep the spacer input separate from the stamped offset so you do not subtract it twice.
Single wheel movement versus axle track
The outward movement result applies to one wheel. Axle centreline track increases by twice that movement only if equal spacer thickness is added to both sides of the axle. An asymmetric installation does not meet that assumption.
Zero thickness is a useful baseline: effective offset remains the stamped value, outward movement is zero and axle track is unchanged. The tool describes an added spacer relative to the same wheel with none; it is not a spacer-stack or hardware-design calculator.
When nominal wheel width helps
Open Advanced only if you also want nominal inner and outer bead-seat positions. Width is optional because the change produced by a spacer does not depend on width. It does not supply missing flange, tire or vehicle dimensions.
To compare different wheels as well as spacers, use Poke & Clearance or the complete fitment comparison. Keeping a spacer-only calculation focused avoids confusing a width change with the spacer's movement.
Example: adding a 10 mm spacer to ET45
Inputs: Stamped offset: 45 mm; Added spacer thickness: 10 mm. Metric results below are computed by the same engine as the live tool.
A 10.0 mm spacer changes ET+45.0 to effective ET+35.0. The same wheel moves outward by 10.0 mm.
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| Measure | Calculated value | Meaning |
|---|---|---|
| Effective offset | ET+35.0 | This describes a mounting-position change, not approval of a spacer installation. |
| Outward movement | 10.0 mm | Inner relative clearance increases by this amount for the same wheel. |
| Symmetric axle track change | +20.0 mm | Only when identical spacer thickness is added on both sides. |
Important limitations
Geometry does not approve spacer hardware or installation. Hub engagement, fastener length, torque, ratings, manufacturer instructions, dynamic clearances and applicable rules require separate verification.
See the calculation methodology and testing and accuracy for precision, unit conventions and the distinction between nominal geometry and physical measurement.