Free wheel and tyre tools
Wheel and tyre fitment checker
Compare wheel width, offset and tyre size together. Estimate inner clearance, outer poke and arch gap changes with a cross-section drawn to scale.
How it works
We estimate mounted section width from the marked tyre width, adjusting by 0.4 mm for each 1 mm the rim differs from our estimated measuring rim. Half that section width plus offset gives the inner reach; half minus offset gives outer reach. The section envelope is a proxy for the tyre shoulder, not a tread measurement. Positive inner-clearance change means more room; positive outer-poke change means further out. With the wheel centre fixed relative to the arch, half the diameter increase is the loss of vertical arch gap. No absolute clearances are inferred.
References
A worked example
Keeping 225/45 R17 tyres but changing a 7.5 inch ET45 wheel to 8 inch ET35 increases estimated section width from 225 to 230.08 mm. Inner clearance increases by 7.46 mm and outer poke increases by 12.54 mm. Nominal diameter and vertical arch gap are unchanged. Actual tyre shape can give different measurements.
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
- 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 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.
- Rolling vs pulling arches: clearance, paint and rust risksCompare arch rolling and pulling, identify what is actually rubbing, and plan bodywork without assuming a guaranteed clearance gain or crack-free paint.
Questions
Will this tell me whether my tyres rub?
No. It estimates position changes from your current setup. Measure existing gaps at full steering lock and throughout suspension travel, and check the actual tyre and wheel. Camber, alignment, body shape, load and tyre deformation are not modelled.
Why does wheel width change the tyre result?
A wider rim can increase mounted section width. This tool uses a common rule of thumb and an estimated measuring rim. The tyre maker's measured dimensions on your intended rim are better evidence. The shaded drawing is a simplified envelope, not a predicted sidewall contour.
What about spacers, brake clearance and lowering?
Subtract any spacer thickness from that wheel's offset before entering it. The tool does not check spoke-to-caliper clearance, hub engagement or mounting hardware. Lowering and camber changes also need separate measurements; the arch-gap result assumes suspension height and wheel-centre position stay unchanged.
Keep checking
Use these results to plan a setup. Confirm fitment, tyre approval and clearances with a qualified professional before buying or fitting parts.