Free wheel and tyre tools
Wheel offset calculator
Compare wheel width and offset to calculate inner clearance and outer poke in millimetres. Preview a spacer and see a cross-section at scale.
How it works
ET is the distance from the wheel centreline to its mounting face, in millimetres. A higher ET moves the wheel inwards. Each extra inch of width adds 12.7 mm on both sides before offset changes. Inner position is half the width in mm + ET; outer position is half the width in mm − ET. A spacer moves both edges outwards by its thickness.
A worked example
Moving from an 8 inch ET45 wheel to a 9 inch ET35 wheel uses 2.7 mm more inner clearance and adds 22.7 mm of outer poke. A theoretical 2.7 mm spacer would restore the original inner edge position but increase outer poke to 25.4 mm. It is a calculation, not a recommended spacer size.
Quick reference
Moving from an 8 inch ET45 wheel
| New wheel | Inner edge | Outer edge |
|---|---|---|
| 8 inch ET35 | 10 mm more room | 10 mm further out |
| 8.5 inch ET45 | 6.3 mm closer to the suspension | 6.3 mm further out |
| 8.5 inch ET35 | 3.7 mm more room | 16.3 mm further out |
| 9 inch ET45 | 12.7 mm closer to the suspension | 12.7 mm further out |
| 9 inch ET35 | 2.7 mm closer to the suspension | 22.7 mm further out |
| 7.5 inch ET45 | 6.3 mm more room | 6.3 mm further in |
| 7.5 inch ET38 | 13.3 mm more room | 0.7 mm further out |
Bead-seat positions only. Tyre shape, brakes, camber and suspension travel are not included.
Explained in our guides
- Wheel offset explained: choosing ET without guessingUnderstand positive and negative wheel offset, calculate inner clearance and outer position, and choose an ET using measurements from your own car.
- Flush, poke and tucked fitment: measure the whole tyreUnderstand flush, poked and tucked wheels, calculate how width and offset change the look, and check clearance beyond a parked side-on photograph.
- Wheel spacers: safety checks and how to choose a sizeCalculate spacer effects on offset and track width, distinguish slip-on and bolt-on systems, and check hub engagement, fasteners and moving clearance.
Questions
What does positive inner change mean?
The new inner wheel edge sits closer to the suspension, using up clearance. A negative inner change gives more room. Outer change is positive when the wheel sticks out further towards the arch.
Can a spacer fix my clearance problem?
A spacer can move the wheel away from the suspension, but it also moves it towards the arch. The suggested thickness only restores the old inner edge position. A professional must check hub engagement, fastener length, load, alignment and available outer clearance before specifying one.
Does this tell me whether the tyre will rub?
No. This compares nominal wheel bead-seat edges. Tyre shoulders, rim flanges, brake spoke clearance, alignment and suspension movement are not represented. Measure the car and check the exact wheel and tyre combination.
Keep checking
Use these results to plan a setup. Confirm fitment, tyre approval and clearances with a qualified professional before buying or fitting parts.