The five numbers a wheel order is built from
Every forged wheel is manufactured to five values. Diameter and width define the size. Offset defines where the wheel's mounting face sits relative to its own centreline. PCD — the bolt pattern — defines the circle the mounting holes sit on and the number of studs or bolts. Centre bore defines the hub hole that centres the wheel on the vehicle.
Two of these are visible to anyone: diameter and width. They are also the two that customers lead with, which is why they get the most attention and cause the least trouble. The other three are effectively invisible on a finished car, and they are where orders fail.
The important thing to understand is that these are not independent. Change the width and you change where both edges of the wheel sit for a given offset. Change the offset and you move the whole wheel in or outboard without changing its width. A specification that quotes a width but not an offset is not a specification — it is half of one.
Why a tape measure alone is not enough
It is tempting to measure the gap between the current wheel and the arch, add that as additional width, and quote the result. That works on the outboard side and tells you nothing about the inboard side, which is usually the real constraint.
The inboard lip has to clear the suspension strut, control arms, brake caliper and any brake cooling ducting. On a car with a large brake package, that clearance can already be tight with the factory wheel. Add width on the outboard side by reducing offset and you have simultaneously moved the inboard lip closer to those components.
This is why we start from the OEM specification for the exact trim rather than from a measurement. The OEM number is a known-good baseline that clears everything as shipped. Adjustments from there are deliberate and can be checked one at a time.
Reading offset off a wheel you have in front of you
Offset is normally stamped or cast on the inside of the wheel, usually as an ET number. Where it is not legible, you can measure it: lay the wheel face-down on a flat surface, measure the distance from the mounting face down to the surface — that is backspacing — then relate it to the wheel's width.
Backspacing and offset describe the same geometry from opposite ends, and you cannot convert between them without knowing the width. That conversion is covered in its own guide, because confusing the two is a common cause of a mis-quoted fitment.
PCD and centre bore: measure, do not guess
Both are easy to measure incorrectly and both matter. PCD is the diameter of the circle passing through the centre of the bolt holes — not the distance between two adjacent holes, which is the mistake people make and which gives a plausible-looking wrong answer. Centre bore is the diameter of the hub hole and must match the vehicle's hub spigot.
We do not recommend spigot rings as a way to bridge a centre-bore mismatch on a custom order. If we are manufacturing the wheel for your car, the correct answer is to build it with the right centre bore in the first place.
What we need from you to confirm a fitment
Send the vehicle make, model, exact trim and model year, the chassis code where you know it, the brake package if there is more than one, any suspension change, and the stance you are targeting. If you have the OEM wheel specification, include it.
We will review that against the clearance envelope and the load rating, propose a specification, and return it to you in writing for approval before anything is cut.
PLACEHOLDER: any specific measurement value quoted to a customer — offset, PCD, centre bore, or a load rating — must come from Fenghuai engineering for the specific vehicle. Nothing on this page should be used as a lookup value.