Wheel Fitment Guide: PCD, Offset and Center Bore

What is wheel fitment?

Wheel fitment is the set of dimensions that decides whether a wheel bolts to your hub and clears your brakes, suspension and bodywork: bolt pattern (PCD), offset (ET), hub center bore (CB), diameter and width. A wheel with the right diameter but the wrong offset will still rub. With off-the-shelf wheels you hunt for the closest match. With forged-to-order wheels you specify the numbers, and the wheel is cut to them — key dimensions held to ±0.05 mm.

Everything below is the same checklist our engineers work from when they price an order. Fill it in and you have a quotable spec sheet.

Staggered setups: list front and rear as two separate lines. A 19×9.5 ET35 front and 19×11 ET25 rear is one order, not two — mixed sizes in a single order are accepted at the 4 pcs MOQ.

How do you measure bolt pattern (PCD)?

PCD, or pitch circle diameter, is the diameter of the imaginary circle drawn through the center of every stud, written as number of studs × diameter in mm. So 5×114.3 means five studs on a 114.3 mm circle. Even-lug patterns are easy — measure straight across. Five-lug patterns have no stud directly opposite, which is where most measuring errors come from.

The general form, for any stud count n, is:

Patterns that look close are not interchangeable: 5×112 and 5×114.3 differ by 2.3 mm, enough to load the studs in shear and crack a wheel. If your hub PCD and your wheel PCD genuinely differ, the fix is a machined wheel adapter, not force. FLEXIFORGED drills your PCD directly into the wheel, so an adapter is rarely needed on a custom order.

What does ET (offset) mean, and how do you choose it?

Offset, marked ET, is the distance in millimetres from the wheel's mounting face to the centerline of the rim. Positive ET puts the mounting face outboard of the centerline and pulls the wheel in toward the suspension. Negative ET pushes it out toward the fender. Zero ET means the mounting face sits exactly on the centerline. Every 1 mm of ET change moves the wheel 1 mm sideways — the single most useful number in this guide.

Converting offset to backspacing

North American shops often work in backspacing — the distance from the mounting face to the inner rim flange. The two describe the same thing:

A 9.5" wide wheel at ET35: (9.5 + 1) ÷ 2 + 1.38 = 6.63" of backspacing. The +1" allows for the two rim flanges outside the quoted bead-seat width. Send us either figure — state which one you used and we convert it.

Because a 2-piece forged wheel assembles a machined center to a barrel, offset can be dialled in during assembly; a monoblock has its offset cut into the billet. Both are made to your ET — the difference is how the number is reached.

Coilovers, big brakes, wide-body? Stock ET is no longer your ET. Tell us what is fitted and what you measured, not what the factory wheel says. We do not publish a fixed ET range, because offset is engineered to your car rather than picked off a shelf: send the measurements and the modifications, and we assess a workable ET and put it on your drawing for approval.

What is center bore, and do you need spigot rings?

The center bore is the machined hole in the back of the wheel that sits over the raised spigot on your hub. When the bore matches the hub, the hub carries the vehicle's weight and the bolts only clamp — that is a hub-centric fit. When the bore is oversized, the bolts carry the load and the wheel is centered by whatever the fitter can manage, which is how steering-wheel vibration at 100 km/h starts.

Mass-produced wheels ship with a large universal bore plus plastic spigot rings to fill the gap. FLEXIFORGED does not work that way: every wheel is CNC-machined to order, so the bore is cut to your hub diameter, held to ±0.05 mm on key dimensions and 100% runout tested to under 0.01". No rings, no shims, no filler.

Measure the outside diameter of the hub spigot with a caliper, in millimetres, to one decimal place. If you cannot reach it, give us the vehicle and the wheel you are running now and note the bore of that wheel.

How do you choose diameter, width and tire size?

Diameter and width set the tire, and the tire sets the clearance. Quote width in inches at the bead seat — the "J" in 9.5J is the flange profile, not the width. Then tell us three things that override every catalog table:

Not every diameter and width pairs with every design — the combination is confirmed on your drawing before anything is cut. If your target sits at the edge of the envelope, send it anyway and we will tell you straight whether it is buildable.

How do you send fitment specs to FLEXIFORGED?

Five steps, about 30 minutes with a caliper. You do not need a CAD file or a wheel designer — you need numbers.

1. Measure the bolt pattern

   Count the studs and apply the formula above. Write it as 5×114.3, not "five lug".

2. Measure the hub center bore

   Outside diameter of the hub spigot, in mm, to one decimal. We machine the wheel bore to match.

3. Decide the offset per axle

   Give ET in mm (or backspacing in inches, stated as such), separately for front and rear.

4. Set diameter, width, tire and finish

   Inches per axle, planned tire size, and the finish: powder coat, brushed, polished, anodized, chrome or custom two-tone.

5. Send it with your quantity and destination port

   Use the quote form or WhatsApp. We reply with pricing and a drawing showing size, offset, center bore and load rating. Nothing is cut until you approve that drawing. Every produced wheel is then engraved with its size, offset, center bore, load rating and serial number, backed by a QC record with photos or video on request. Samples take 10–15 working days; production 20–30 working days.

What are the most common fitment mistakes?

These six account for nearly every "the wheels don't fit" message we receive. All are avoidable before the order is placed.

Which of these are you?

Fitment questions arrive from three directions. Tell us which one you are and we route you to the right engineer.

Wheel fitment FAQ