Wheel Size & Offset Calculator
Will they fit? Compare a new wheel and tire against your factory setup — poke, inset toward the strut, rolling diameter, ride height and speedometer error — with the same to-scale side-view diagram our shop uses.
Start from your vehicle
Optional — pick your car and we fill in the factory size. Or type the sizes below.
Front
| OEM | New | Change | |
|---|---|---|---|
| Wheel | – | – | |
| Tire | – | – | |
| Overall diameter | – | – | |
| Circumference | – | – | |
| Poke (outer face) | – | – | |
| Inset (inner face) | – | – | |
| Speedometer at a true 100 km/h | – | – | |
| Ride height | – | – | |
| Fender gap | – | – |
Orange = factory, blue = new. Drawn to scale from the numbers above; the strut is a generic MacPherson layout, not your car's.
Rear
| OEM | New | Change | |
|---|---|---|---|
| Wheel | – | – | |
| Tire | – | – | |
| Overall diameter | – | – | |
| Circumference | – | – | |
| Poke (outer face) | – | – | |
| Inset (inner face) | – | – | |
| Speedometer at a true 100 km/h | – | – | |
| Ride height | – | – | |
| Fender gap | – | – |
Orange = factory, blue = new. Drawn to scale from the numbers above; the strut is a generic MacPherson layout, not your car's.
Estimates from tire geometry. Brakes, fender liners, suspension travel and the tire's actual make are not modelled — we confirm every fitment on the car before we quote it.
Only changing tires? Use the tire size calculator →
How to use it
- Pick your vehicle (optional) — the factory rim size, offset and tire size fill the first group, with the bolt pattern and centre bore shown underneath. Not listed? Type them from the wheel's stamping and the door-jamb placard.
- Change only what differs in the second group. "Start from OEM" copies the first group across; change the rim diameter and the aspect ratio switches to the one that keeps the factory rolling diameter, until you type one yourself.
- Read the diagram and the summary. The orange outline is the factory wheel, the blue fill the new one, with the strut faded behind. An Inset row marked "closer to strut" is the direction that needs checking most.
Reading the numbers
Poke is where the outer face sits relative to the hub, inset where the inner face sits — half the rim width minus or plus the offset. Overall diameter uses the same model as willtheyfit.com: a tire on a rim wider or narrower than itself tilts its sidewall, so the upright height is √(sidewall² − stretch²), which is why the same size reads a few millimetres different on different rim widths. The speedometer row is what the gauge shows at a true 100 km/h; ride height and fender gap each move by half the diameter change.
Looking for OE-fitment wheels? The OEP catalogue is searchable by bolt pattern and size, and our winter tire & wheel packages come with the fitment already checked.
Common questions
What is wheel offset (ET)?
The distance, in millimetres, from the wheel's mounting face to its centreline. A higher (more positive) offset tucks the wheel further into the fender; a lower offset pushes it out. It is stamped on the back of every wheel as ET followed by the number — ET40, ET35 and so on.
What are poke and inset?
Poke is how far the outer face of the wheel sits from the hub — more poke means the wheel stands out closer to the fender lip. Inset is the same measurement on the inner face, toward the strut and brake. A wider wheel or a lower offset adds poke; a wider wheel or a higher offset adds inset. The calculator reports both as a change from your factory wheel, in millimetres.
Does the calculator check bolt pattern and centre bore?
It shows your car's factory bolt pattern and centre bore when you pick the vehicle, but it does not judge a wheel against them — those two simply have to match (a larger bore can be adapted with a hub-centric ring; a different bolt pattern cannot). We check both on every wheel before it goes on a car.
How much poke or inset change is safe?
On most cars a few millimetres either way is invisible; around 10 mm more poke starts to matter on cars with little fender room, and any move toward the strut needs checking against the actual strut and brake caliper. Keep the overall diameter within about 3% so the speedometer and ABS stay honest. These are estimates from geometry — we confirm on the car before we quote.
Where do the numbers and the diagram come from?
The geometry is a port of willtheyfit.com's model, validated against it, and it is the same one our shop uses in its own fitment tool. Factory specs come from an OEM fitment database; if your car is not listed, type its wheel size, offset and tire size from the placard and the wheel's stamping.
Want us to check it on your car?
Send us the sizes you compared and your vehicle — we confirm the fitment and email an all-in installed price.