Wheel Spacer Calculator
Calculate how an added spacer changes effective offset, wheel position and axle centerline track.
The wheel itself stays the same. This compares adding the same spacer on each side of an axle.
Compare a complete setup ↗This does not verify spacer suitability, fastening length, hub engagement, or vehicle clearance.
How a spacer changes wheel offset
Enter the wheel’s stamped ET and the spacer thickness in millimeters. Effective offset equals wheel offset minus spacer thickness. A spacer moves the same wheel and tire outward without changing their width or diameter.
Worked example: ET45 with a 10 mm spacer
45 − 10 = ET35. Relative to that wheel with no spacer, its outer edge moves 10 mm outward and its inner edge moves 10 mm away from the suspension. Using a 10 mm spacer on each side increases wheel-centerline track across the axle by 20 mm.
Does the calculator recommend a spacer thickness?
No. It describes the position change for the thickness you enter. Measure clearance and verify the spacer, hub, wheel and fastening hardware with their manufacturers. It does not evaluate hub engagement, thread engagement, centering or structural suitability.
What if I am replacing an existing spacer?
Compare the new thickness with the old one. Replacing a 5 mm spacer with a 10 mm spacer adds 5 mm of outward movement per wheel, not 10 mm. Calculate both effective offsets or enter them in the wheel offset comparison.
Can I calculate a target effective offset?
Required spacer thickness = stamped ET − target ET. For ET45 to become ET35, the geometric difference is 10 mm. A negative result means adding a spacer cannot reach that target on the same wheel.
Offset definitions: Discount Tire’s offset and backspacing guide. Use the full wheel comparison when changing wheel width or tires at the same time.