In short. Wheel designs fall into about seven families: spoke (five to seven broad arms), split-spoke (each arm divides in a V or a Y), multi-spoke (ten to twenty thin arms), mesh (fine crossing bars), honeycomb (closed diamond or hexagonal cells), turbine (curved or twisted arms, like fan blades) and closed or "aero" faces. No law or standard fixes these names. Beyond looks, the design changes one thing that has been measured well: how much of the face is closed. In a wind tunnel, going from rims 40 % covered to 90 % covered cut a car's drag coefficient by 0.012 (Chalmers and Volvo Cars, 2019); the more open the wheel, the more air reaches the brakes.
The seven families, and how to recognise them
The table below is our own classification, built on what you can see and on what the studies we read measured. "Open area" is an order of magnitude, not a measurement: it depends on the width of the arms and varies a lot within one family. "Air to the brakes" is our reading of the simulations cited below, not a measurement for each style. "Windows" is the number of openings you clean, counted by us on a typical example.
| Style | How to recognise it | Open area | Drag (studies read) | Air to the brakes | Windows to clean | Mounting side |
|---|---|---|---|---|---|---|
| Spoke (5, 6 or 7 arms) | Broad arms running from the centre to the rim | Medium to large | Mostly depends on how much of the face is closed | Good | 5 to 7 | Either side if the arms are straight |
| Split-spoke (double spoke, Y-spoke) | Each arm divides in two, in a V or a Y | Large | As above | Good | 10 to 14 | Either side if the arms are straight |
| Multi-spoke | 10 to 20 thin arms, sometimes grouped | Large | As above; rounded spoke edges cut the drag of a rotating wheel (Bolzon, 2019) | Very good | 10 to 20 | Either side if the arms are straight |
| Mesh (cross-spoke) | Fine bars crossing each other, often on two levels; you see the brake through it | Large | Not measured in the studies we read | Good | Several dozen, with corners where bars cross | Either side |
| Honeycomb | Closed cells, diamond or hexagonal, across the whole face | Medium | Not measured in the studies we read; by coverage, the more closed, the lower | Medium | Several dozen, each with four or six walls | Either side |
| Turbine (directional) | Curved or twisted arms, like fan blades | Medium to large | The fan-spoke rim was the worst shape tried on a model (Bolzon, 2019) | The twist angle matters (Kang, 2013) | 5 to 20 | Respect it when the wheel comes in left and right versions |
| Closed or aero (with inserts) | An almost solid face, or inserts between the arms | Small | The lowest: the more closed the face, the lower the drag (Brandt, 2019) | Low | Few, but little access to the barrel | Either side, unless the design is orientated |
A true wire wheel is made of tensioned metal wires, as on a classic car; an alloy wheel has arms, which galleries call spokes too. "Deep dish" or "concave" is not a style of face but a profile any family can take: our guide to deep dish and concave wheels explains how the lip and the face depth are made, and the guide to the parts of a wheel names the barrel, lip, face and centre bore.
Is there an official list of rim style names?
No. The closest thing is the US Patent and Trademark Office's design classification. In class D12, subclass 204 is "Wheel or wheel cover (includes hub or rim)", and the subclasses beneath sort wheels by shape, not by marketing names: 205 "Wire-type spoke", 206 "With air diverter, e.g., vane or scoop", 207 hub, 208 rim, 209 "Aperture or simulated aperture", then apertures with a circular motif, apertures with two straight sides, concentric circles, and element or attachment (subclasses 210 to 213). The names "split-spoke", "mesh" or "turbine" are trade terms, and the same word may cover different shapes from one catalogue to the next: trust the photo, not the label.
What the design changes to drag
This is the best measured effect. The wheels weigh heavily in a car's air resistance: "approximately 25 % of a passenger vehicle's aerodynamic drag comes directly or indirectly from its wheels", according to Brandt, Berg, Bolzon and their co-authors (SAE Technical Paper 2019-01-0662, April 2019). They worked in the Volvo wind tunnel on a saloon and an estate with 245/45 R18 tyres and modular rims.
Their main finding fits in one sentence: "the most important parameter was the coverage area, and it was found to have a linear effect on the aerodynamic drag". Table 5 of the paper gives the figures:
| Front rims | Rear rims | Change in drag coefficient, cooling inlets open | Cooling inlets closed |
|---|---|---|---|
| 40 % covered | 40 % covered | reference | reference |
| 40 % covered | 90 % covered | −0.008 | −0.008 |
| 90 % covered | 40 % covered | −0.004 | −0.005 |
| 90 % covered | 90 % covered | −0.012 | −0.013 |
Closing the rear rims gained more than closing the fronts, and the two gains add up. The outer radial region of the wheel and the depth of the centre also counted, less than coverage.
A second study from the same group (Bolzon, Sebben and Broniewicz, International Journal of Automotive Technology, 2019), on a one-fifth scale model, found the same direction: "Reducing the rim coverage area increased the drag coefficient." It adds two results that bear directly on styles: "The fan spoke rim performed the worst, regardless of rotation", and "Rounding the spoke edges reduced the drag coefficient of a rotating wheel."
Car makers draw wheels for the air as a result. BMW presented "Aerodynamic Wheels" for the electric iX3 on 5 February 2020: a cast aluminium base wheel with inserts whose aerodynamic and weight benefits together, the release says, lower power consumption by another 2 % in the European WLTP cycle, or 0.4 kWh per 100 km and about 10 km of range.
Our calculation: what 0.012 of drag coefficient is worth on the road
Drag force is F = ½ × ρ × ΔCD × A × v². Our assumptions: air density ρ = 1.2 kg/m³, frontal area A = 2.3 m² (the order of magnitude of a saloon, not the figure of any particular car), ΔCD = 0.012, the wind-tunnel gap between rims 40 % and 90 % covered.
| Speed | Extra drag force | Power absorbed | Energy at the wheels per 100 miles | Per 100 km |
|---|---|---|---|---|
| 30 mph (48 km/h) | 3.0 N | 40 W | 0.13 kWh | 0.08 kWh |
| 50 mph (80 km/h) | 8.3 N | 185 W | 0.37 kWh | 0.23 kWh |
| 70 mph (113 km/h) | 16.2 N | 507 W | 0.72 kWh | 0.45 kWh |
| 80 mph (129 km/h) | 21.2 N | 757 W | 0.95 kWh | 0.59 kWh |
Energy is the force multiplied by the distance (160,934 m for 100 miles), converted to kilowatt-hours. It grows with the square of the speed: the choice shows on the motorway or interstate, hardly in town. The result is of the same order as BMW's 0.4 kWh per 100 km on the mixed WLTP cycle, and counts the air only, not weight or motor efficiency.
What the design changes to the brakes
Here openness works the other way. Kang, Zheng and Liu (Proceedings of the IMechE, Part D, 2013) simulated airflow around a brake disc behind several wheel designs. They conclude that the spoke type has a significant influence on the flow and on the disc's convective cooling; with no twist, "the convective cooling performance of the disc of a five-spoke wheel is better than that of the baseline", and on a six-spoke wheel, cooling improved as the twist angle of the spokes increased. Bhardwaj (SAE Technical Paper 2017-01-1537, 28 March 2017) simulated a different wheel-centre shape: the axial airflow through the wheel rose from 0.04 to 0.47 m³ per minute, and the brake disc's heat transfer coefficient was about 33 % to 50 % higher.
These are simulations without disc temperatures in real use. What we take from them: a closed wheel leaves less air for the brakes, an open one more, and the shape of the arms counts as much as their number. For a road car driven normally, no source we read shows that a closed original-equipment wheel overheats the brakes; for track days or long mountain descents, the question is one for the maker of the car.
The design also matters for space. Flat or deeply concave arms pass closer to or further from the caliper, and it is the inner profile of the arms that decides whether a wheel clears a big brake, not its style; our guide to brake caliper clearance shows how that gap is read.
What the design changes to cleaning
No study we read measures cleaning time. Our reading comes from geometry: each window adds flanks and corners where brake dust settles. A five-spoke has five windows; a split five-spoke has ten; mesh and honeycomb have several dozen, with crossings a brush reaches badly. A closed face washes quickly but gives little access to the barrel behind it.
The finish matters as much as the shape: a diamond-cut or polished face is not treated like a matt paint. Our guide to cleaning alloy wheels safely gives the products and the method, and the one on finishes and colours what each finish will take.
What the design changes to weight
No source we found compares the weight of two styles at equal size, material and process. What you feel when driving depends on where the metal sits.
Our calculation: a wheel's rotational inertia adds up each mass multiplied by the square of its distance from the axis. 200 g of metal at 0.20 m from the axis (about 7.9 in, near the rim) counts (0.20 / 0.06)² = 11 times as much as the same 200 g at 0.06 m (about 2.4 in, near the hub). A mesh wheel whose bars gather near the rim can therefore weigh more in rotation than a five-spoke of the same mass. Our guide to lightweight wheels and unsprung weight explains what a lighter wheel changes.
Turbine and directional wheels: left and right
A turbine wheel has curved or twisted arms. When the design is orientated, there are two cases: the maker produces a left-hand and a right-hand version, so that the arms "turn" the same way on both sides of the car, or it produces a single version and the arms run backwards on one side.
Kang's study shows that the twist angle changes disc cooling, but no study we found compares the two directions of rotation. Our reading: a twisted arm acts like a blade, so swapping a left wheel to the right reverses its effect as well as the intended look. If your wheels come in two versions, the maker's sheet or a mark on the wheel says so. Keep each wheel on its side, and remember it at every rotation, which can then only go front to back on the same side, as with directional tyres: see our guides to directional wheels and to tyre rotation patterns.
What the rules say about wheel design
No text we read reserves a wheel style for one type of car. The rules that touch design concern sharp projections, and damage.
Europe and the UK, new cars. UN Regulation No. 26 on external projections of passenger cars, which we read in its 03 series, supplement 1 (in force from 11 June 2007, published in the Official Journal of the European Union), says in paragraph 6.7.2: "The wheels, wheel nuts, hub caps and wheel discs shall not exhibit any pointed or sharp projections that extend beyond the external plane of the wheel rim. Wing nuts shall not be allowed." Paragraph 6.7.3 adds that, with the car travelling in a straight line, no part of the wheels other than the tyres above the axle line may project beyond the vertical projection of the body; wheel discs covering the nuts may project by no more than 30 mm, with a radius of curvature of at least 30 mm. The regulation sets what a new car model must meet before sale; we have not checked the latest version, nor how each country applies it to a wheel changed afterwards. Spiked caps, sharp decorative nuts and wing nuts fall outside it.
UK, the MOT. The inspection manual does not judge style but condition. In section 5.2.2, "any fracture or welding defect on a wheel" is a dangerous defect, "a wheel and its fixings not compatible" is major, and a wheel distorted to the point the wheel or tyre is likely to become detached is dangerous; section 5.2.1 makes a loose or missing wheel nut, bolt or stud a major defect, and more than one a dangerous defect. After a pothole, look closely at fine arms: if you see a crack in a spoke, have the wheel checked before you drive on.
United States. The federal standard on wheel nuts, wheel discs and hub caps, 49 CFR 571.211 (FMVSS No. 211), appears in the eCFR as "[Reserved]", in the version dated 27 December 2016: it is no longer in force at federal level. We did not read state equipment laws, which may still cover projecting ornaments.
Australia and Canada. We did not find and read a national text on wheel projections for this guide. Check with your state or provincial roadworthiness inspection before fitting caps or nuts that stand proud of the wheel.
Which style for which car?
There is no rule, and Onyx Forged does not recommend a size or an offset: the style is a matter of taste, while the size, offset, bolt pattern and load rating come from the documents of your car's maker. A few points help you see clearly.
- Use first. On long motorway runs a closed wheel costs less energy; on a track or in the mountains, an open wheel leaves more air for the brakes.
- The time you want to spend washing. A broad five-spoke is cleaned in minutes; a mesh or a honeycomb takes much longer.
- Proportions. Thin, numerous arms make a large wheel look lighter; broad arms give weight to a tall car.
- Colour. A busy design reads better in a single colour, a simple one can carry a diamond-cut face or two tones; our finishes guide covers the options.
To compare two wheels' positions in the arch, the wheel offset calculator helps; it does not replace your car maker's documents.
Frequently asked questions
What are the main rim styles called?
In trade use: spoke (five to seven broad arms), split-spoke or double spoke, multi-spoke, mesh, honeycomb, turbine and closed or aero faces. No standard fixes these names, and catalogues use them loosely.
What is the difference between mesh and honeycomb wheels?
In our terms, mesh is a lattice of thin bars crossing each other, often on two levels, through which you see the brake; honeycomb cuts the face into closed cells, diamond or hexagonal. Listings often confuse the two, so go by the photo.
What is a split-spoke wheel?
A wheel whose arms each divide in two, in a V or a Y, between the centre and the rim. It doubles the number of windows compared with the same number of single spokes.
Do open spokes cool the brakes better?
The simulations we read point that way: more openness and a suitable arm shape send more air to the disc. They do not give temperatures in real use, and no source we read shows that a closed original-equipment wheel overheats the brakes in normal driving.
Do aero or closed wheels really add range?
In the wind tunnel, going from rims 40 % covered to 90 % covered cut the drag coefficient by 0.012 on the test cars. Our calculation turns that into about 0.72 kWh per 100 miles at 70 mph and 0.13 kWh at 30 mph; BMW gives 0.4 kWh per 100 km and about 10 km of WLTP range for the aerodynamic wheels of its iX3.
Do turbine wheels have a mounting side?
Only when the maker produces left and right versions. The sheet or a mark on the wheel says so; then each wheel stays on its side and rotation goes front to back only.
Are spiked wheel caps or spinners legal?
For new cars, UN Regulation No. 26 forbids sharp projections of wheels, nuts and hub caps beyond the outer plane of the rim, and wing nuts. The US federal standard 571.211 is shown as reserved; state laws vary.
See the designs
Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards. Its designs, from single spokes to closed faces, are in the catalogue.
Sources
- A. Brandt, H. Berg, M. Bolzon et al., The Effects of Wheel Design on the Aerodynamic Drag of Passenger Vehicles, SAE Technical Paper 2019-01-0662, April 2019.
- M. Bolzon, S. Sebben, A. Broniewicz, Effects of Wheel Configuration on the Flow Field and the Drag Coefficient of a Passenger Vehicle, International Journal of Automotive Technology, 2019, record and abstract.
- N. Kang, W. Zheng, X. Liu, An investigation of the influence of the wheel spoke type on the convective cooling of the brake disc, Proceedings of the IMechE, Part D, 2013, record and abstract.
- A. Bhardwaj, A CFD Investigation of Aerodynamic Effects of Wheel Center Geometry on Brake Cooling, SAE Technical Paper 2017-01-1537, 28 March 2017, abstract.
- BMW Group, Novel Aerodynamic Wheels for the purely electric BMW iX3, press release of 5 February 2020.
- UN Regulation No. 26, external projections, 03 series, supplement 1, text published in the Official Journal of the European Union, reproduced by Lexaris.
- GOV.UK, MOT inspection manual for private passenger and light commercial vehicles, section 5.
- eCFR, 49 CFR 571.211, version history.
- USPTO, Class D12 schedule, subclasses 204 to 213.
All pages were read on 16 October 2026.
The Onyx Forged design office.