In short. By eye, often not. No regulation asks a wheel to carry the word "FORGED", and a cast wheel can have a fully machined face. To tell whether a wheel is forged, put four clues together, from the most reliable to the least: the documents (an OE part number, the maker's specification, the E-mark file that names the method of production), the markings, the marks left by manufacture on the back and in the windows (machining everywhere, or as-cast skin, flash and vent marks), and the weight, but only against a wheel of the same size whose weight comes from the same source. Price proves nothing, though a low one should make you ask questions. Tapping the wheel or holding a magnet to it proves nothing at all.
This guide starts from a wheel or an advert. For the processes themselves, read our guide to forged, cast and flow-formed wheels and how forged wheels are made.
1. Markings: what a wheel must say, and what it need not
Three texts set what a wheel carries.
| Text | Markings required | The process? |
|---|---|---|
| UN Regulation No. 124, replacement wheels (§ 4.4 and 5.1) | maker's name or trade mark, rim designation, inset (offset), date of manufacture (at least month and year), part number, and the E-mark: an E in a circle followed by the number of the country that granted it, then "124R-" and the approval number | no |
| Japanese JWL standard (MLIT, § 4.1) | the JWL mark, size and offset, the name of the wheel or vehicle maker, and for a wheel meant for certain vehicles a symbol for them; cast in or stamped | no |
| German permit No. 48207, an aftermarket alloy wheel (KBA, § IV.2) | permit number outside; inside, among others, type, trade mark, a "foundry mark", size, version, bolt pattern, offset and date | no |
None of the three asks for the process. "FORGED" on a wheel is therefore the maker's own claim, which no rule governs, and raised lettering can be copied. The process does appear in the paperwork: Regulation No. 124 lists the "method of production (welded, forged, cast,…)" among the characteristics that define a wheel type (§ 2.2.7), and the communication form issued by the authority that grants the E-mark has a line for "Method of production" (Annex 1, item 2.3). That document, not the wheel, is where the process is written down.
Two limits. First, the regulation "does not apply" to original equipment (OE) wheels, to the car maker's own replacement wheels, or to special wheels of another width or diameter, which stay under national rules (§ 1 and 2.5): an OE wheel, like many aftermarket wheels, carries no E124R mark, and its absence means nothing. Second, JWL and VIA refer to fatigue and impact trials, not to how the wheel was shaped: the trials are the same for cast and forged wheels, apart from one optional factor (see how to read wheel markings).
One clue works the other way: a mark that the wheel's permit or specification calls a foundry mark ("Gießereizeichen" in the German permit) means the wheel was cast. To trace an OE wheel from its numbers, see how to identify OE wheels.
2. "Forged" covers more than one process
NAPAC, the Japanese automotive parts and accessories aftermarket association, which includes the JAWA wheel division, lists three forging processes, not one:
| Family | Process | Starting point |
|---|---|---|
| Casting | gravity, low-pressure, die, squeeze | molten alloy poured or injected into a mould (squeeze: pressed at 700 to 1,000 kg/cm² while it solidifies) |
| Forging | hot forging | a solid aluminium billet, heated to about 400 to 500 °C and pressed several times |
| Forging | molten-metal forging | molten alloy fed into the die, pressed at 300 to 1,500 kg/cm² while it solidifies |
| Forging | semi-solid forging | a billet of electromagnetically stirred A357 alloy, heated to a semi-molten state, then injected into the die |
The JWL standard itself mentions "cast-forged" alloys, for which it allows an optional factor in the bending trial (§ 2.1.1). A wheel sold as forged can therefore start from molten metal. The useful question, to put to the maker in writing, is: "a solid billet or a molten alloy?" A flow-formed wheel keeps a cast centre; only its barrel has been spun.
3. Marks of manufacture: where to look
A cast wheel comes out of a mould in several parts. According to a US patent on low-pressure casting of wheels, the lower die forms the design face, a pair of side dies forms the outside of the barrel, the upper die forms the back, and the alloy enters through the centre, at the hub, where the sprue is removed by finish machining (US 6,837,549 B2). The same text describes a design face left substantially as-cast, and also considers a face machined all over. The mould must also let the air out, through thin flash at the parting lines or through vents in the die (Open University).
A forged wheel starts as a billet pressed in a closed die. The metal squeezed out of the die, the flash, is removed after forging, and dies for aluminium usually have a draft of at least 3 degrees (Wikipedia, Forging). Pressing gives less intricate shapes than casting (French Wikipedia's article on forging makes the point), so most of the design is cut by machining.
Take a torch, clean the back of the wheel and look at a low angle:
| Where to look | Points to cast | Points to forged |
|---|---|---|
| Walls of the windows, between the spokes | mould surface, no tool marks | regular cutter marks, machined edges |
| Back of the spokes and of the centre | as-cast skin, sometimes the imprint of a vent | machined; where the cutter did not go, the smooth surface of the die |
| Joins | a fine line or a dressed-off flash where two parts of the mould met, unless machining removed it | the line where the flash was trimmed, usually machined away |
| Design face | machined or as-cast: settles nothing | usually machined |
| Centre | machined: the sprue was there | machined |
Three traps. A machined face proves nothing: the patent considers a cast wheel with its face machined all over. Draft, the slight angle of the walls that lets the part out of the tool, exists on both: the patent discusses it on as-cast faces, and forging dies have it too. And thick paint hides the marks: look where it is thinnest, deep in the windows and inside the barrel.
4. Weight: only at the same size, and only from one source
Weight only compares two bare wheels of the same diameter, width and close offset, and only if one source gives both weights, which is rare. In the press material of two car makers, the only figure we found is BMW's: on 27 August 2015 it described 21-inch forged wheels as "around two kilos lighter than comparable standard aluminium cast wheels". Even there, the maker gives a difference, not the two weights.
Three reasons not to decide on the scales:
- Density works against the forged wheel. On typical values, cast A356-T6 is 2.6 g/cm³ and forged 6061-T6 2.7 g/cm³ (MakeItFrom): at equal volume, an 11 kg wheel in 6061-T6 (4.07 litres) would weigh 10.6 kg in A356-T6. A forged wheel is lighter only if it holds less metal.
- The casting process matters too. According to NAPAC, a squeeze-cast wheel can be 10 to 15 per cent lighter than a one-piece low-pressure wheel of the same size.
- The design matters more than the process. A well-designed cast wheel can weigh less than a heavy forged one. What weight changes on the car: our guide to unsprung weight.
5. Documents: the most reliable clue
OE wheel. Have the part number cast or stamped inside looked up in the car maker's parts catalogue. A maker's data often name the process: BMW's published technical data for the M3 CS (25 January 2023) read "9.5J x 19 forged light alloy" at the front. If the part number leads to a wheel described as cast, that settles it.
Aftermarket wheel. Ask the maker in writing, not only the seller: the part number, the alloy and its grade (6061-T6, A356, or "aluminium" with no grade), and the process for the centre and for the barrel. For a wheel marked E124R, the number that follows leads to the authority's file, whose form names the method of production.
Used wheels from an advert. Ask for sharp photos of the markings, the back of the spokes and the walls of the windows, the original invoice if there is one, and the weight of one bare wheel with its size. The other checks before you pay (buckles, cracks, PCD, load) are in our guide to buying used alloy wheels.
The only formal proof destroys the part: a polished and etched section shows whether the solidification structure of the metal has been replaced by the fibrous structure of forging (French Wikipedia). Nobody does it on a wheel they want to keep.
In Great Britain, the MOT does not ask how a wheel was made: it looks for fractures, welding defects and distortion (MOT inspection manual, section 5.2).
6. Price: a warning, not a proof
Our guide to what forged wheels cost sets out published prices; in its table, a flow-formed wheel costs about a third of a made-to-order forged one. A "forged" set priced like a cast or flow-formed one is not necessarily misdescribed, but it is a reason to ask for the documents in section 5. A high price, on its own, proves nothing.
7. Tapping and magnets: two tests that fail
Magnet. Aluminium is paramagnetic, "essentially unaffected by static magnetic fields" (Wikipedia, Aluminium). A magnet will not hold on a cast wheel or on a forged one: it tells steel from alloy, not one process from another.
Tapping. The sound a wheel makes when struck depends on its shape, its wall thickness, how it is held and whether a tyre is fitted. None of the texts we read uses sound to identify a process; the JWL trials even look for cracks with dye penetrant, not by ear.
Fake forged wheels: what the phrase covers
"Fake" covers two cases: a cast or flow-formed wheel described as forged, for which the checks above apply, starting with the documents; and a copy sold under another brand's name, for which you buy through that brand's own channels and check the part number with it. In both cases the lettering alone settles nothing.
If the wheel is one of ours
Our monoblock wheels are forged 6061-T6 aluminium, 5-axis CNC machined from a single piece (see, for example, the OX-G6 Vector), and all Onyx Forged wheels are designed to JWL/VIA standards. The measurements of each set are submitted to you in writing before machining, and customer service answers any question about one of our wheels. See our monoblock wheels and the catalogue.
Frequently asked questions
How can you tell if wheels are forged?
By putting the clues together: a document from the wheel maker or the car maker that names the process, the part number, machining marks in the windows and on the back, and the weight against a wheel of the same size. No visual clue settles it alone; the only formal proof is a section through the metal, which destroys the wheel.
Does "FORGED" on a wheel prove it is forged?
No. Neither UN Regulation No. 124, nor the JWL standard, nor the German permit we read asks for the process to be marked: the word is the maker's claim, and it can be copied.
What are forged rims?
Usually wheels pressed from a solid aluminium billet, then machined, rather than poured into a mould; some processes sold as forging start from molten alloy (section 2). In Britain they are also called forged alloys.
Are forged wheels good?
They can use less metal for the same strength, because the forged alloy has a higher yield strength on typical data. A well-designed cast wheel is a sound road wheel, and a poorly designed forged one is not a good wheel; the forged vs cast guide gives the figures.
Are forged wheels always lighter?
No. The usual forged alloy is slightly denser (2.7 against 2.6 g/cm³); a well-designed cast wheel can weigh less than a heavy forged one.
Is a flow-formed wheel forged?
No. Its centre is cast; only the barrel has been spun on a mandrel.
Can a magnet tell a forged wheel?
No. Aluminium does not attract a magnet, whether it was cast or forged.
Sources
- UN Regulation No. 124: § 1, 2.2.7, 2.5, 4.4, 5.1, Annex 1 (item 2.3) and Annex 3.
- Japanese transport ministry, technical standard for light-alloy disc wheels (7 July 2008), § 2.1.1 and 4.1, in Japanese.
- NAPAC, quality criteria for aluminium wheels (JAWA division) and manufacturing processes for light-alloy wheels, in Japanese.
- Kraftfahrt-Bundesamt, permit No. 48207 and test report (permit of 5 November 2010, report of 18 October 2010), § IV.2, in German.
- US patent 6,837,549 B2, low-pressure casting of a light-alloy wheel.
- The Open University, Low pressure die casting (2 November 2017).
- Wikipedia, Forging and Aluminium; French Wikipedia, article on forging.
- MakeItFrom, A356.0-T6 and 6061-T6: typical densities.
- BMW Group PressClub, original BMW accessories, autumn 2015 (27 August 2015) and BMW M3 CS (25 January 2023).
- GOV.UK, MOT inspection manual, section 5.
All pages were read on 21 October 2026.
The Onyx Forged design office.
