In short. A deep dish wheel is one whose mounting face sits a long way inside the outer lip, so the lip stands proud of the spokes. A concave wheel is one whose face curves inwards from the lip towards the hub. The two go together but are not the same thing: depth comes from the width and the offset, and concavity from how the spokes are shaped within that depth. You can put a number on the depth. The distance from the mounting face to the outer edge of the rim is half the width minus the offset (width ÷ 2 − ET): 56 mm on the front wheel of a Porsche 911 (992), 114 mm on an Audi RS 6, 152 mm on a 12J ET0 and 196 mm on a 12J ET-44. That figure is the most the dish can be; the spokes can stand out beyond the mounting face. A deeper dish means a lower offset, a wider rim, or both, which moves the wheel out and changes the track, so the outside of the wheel and the arch are where it has to be checked. Neither UN Regulation No. 124 nor the MOT manual uses the words "deep dish": a wheel goes through the trials at its own offset, and in Great Britain it is judged like any other.
Two words for two things
Deep dish describes where the face is. The mounting face, the flat surface that sits against the hub, is far from the outer lip, so seen from the side the barrel stands out like the rim of a dish. It is a statement about width and offset.
Concave describes the shape of the face. On a concave wheel the spokes curve inwards, from the outer edge towards the centre, so the wheel looks sunken. It is a statement about the design of the spokes.
A wheel can be deep without being concave (a wheel with straight spokes and a low offset) and concave without being very deep (a wheel with a moderate offset whose spokes still curve). In practice the two are often sold together, since a deeper dish leaves more room for the spokes to curve. The terms are loose: we found no definition of either in UN Regulation No. 124 or in the vocabulary clause of ISO 3911 that we could read. In cycling, "deep dish" describes a different thing, a deep rim section; this guide is about car wheels.
Putting a number on the depth
Our guide to wheel offset gives two positions, measured from the mounting face, which stays where the hub puts it:
- outer edge = width ÷ 2 − ET
- inner edge = width ÷ 2 + ET
Widths are in millimetres; an inch of width is 25.4 mm (NIST). The positions are taken between the flanges, where the width is printed, so the actual lip stands a little further out. The first line is the nominal depth of the dish: the most the face can be recessed if its spokes sit in the plane of the mounting face. A wheel whose spokes stand out beyond the mounting face has a shallower visible dish than this figure.
| Wheel | Width | Offset | Outer edge from the mounting face | Inner edge from the mounting face |
|---|---|---|---|---|
| Porsche 911 (992), front, 19-inch (original) | 8.5J | RO 52 | 55.9 mm (2.2 in) | 159.9 mm |
| Arithmetic example | 8J | ET45 | 56.6 mm (2.2 in) | 146.6 mm |
| Porsche 911 Turbo, front (original) | 9J | RO 41 | 73.3 mm (2.9 in) | 155.3 mm |
| Porsche 911 (992), rear, 21-inch (original) | 11.5J | RO 67 | 79.0 mm (3.1 in) | 213.0 mm |
| Tesla Model 3, front, 19 or 20-inch (original) | 9J | ET34 | 80.3 mm (3.2 in) | 148.3 mm |
| Tesla Model 3, rear, 19 or 20-inch (original) | 10J | ET45 | 82.0 mm (3.2 in) | 172.0 mm |
| Arithmetic example | 10J | ET20 | 107.0 mm (4.2 in) | 147.0 mm |
| Audi RS 6 Avant, winter wheel, 22-inch (original) | 10.5J | ET19 | 114.3 mm (4.5 in) | 152.3 mm |
| Arithmetic example | 12J | ET0 | 152.4 mm (6.0 in) | 152.4 mm |
| Arithmetic example | 12J | ET-20 | 172.4 mm (6.8 in) | 132.4 mm |
| Arithmetic example | 12J | ET-44 | 196.4 mm (7.7 in) | 108.4 mm |
The rows marked original are read in the manufacturers' own documents: the Porsche bulletin 38/25, the Tesla service manual and an Audi parts listing. Two things come out of it.
- "Deep" is not a threshold. The original wheels in the table run from 56 to 114 mm, and an Audi RS 6 wheel is already deeper than a Tesla's. No standard or regulation sets a depth at which a wheel becomes "deep dish".
- The depth is added on the outside. Compare 8J ET45 with 10J ET20: the outer edge moves from 56.6 to 107.0 mm, 50 mm further out, while the inner edge moves from 146.6 to 147.0 mm, under half a millimetre. Each millimetre taken off the ET and each inch added to the width go outwards, and the inner side, towards the suspension and the brakes, barely changes. That is why the question on a deep dish wheel is usually the arch, not the brake caliper. Two wheels of the same diameter and ET can still differ on the inside, depending on the shape of their inner spokes.
The wheel offset calculator gives these two edges for any two wheels you want to compare.
Why most original wheels are flat
Cars with very deep wheels used to be normal. The Autopian's suspension engineer, Huibert Mees, explains why they stopped being so (The Autopian). Old steering boxes did not send road forces back to the driver, so a kingpin set far inboard, with a large scrub radius and kingpin offset, amplified braking and pothole forces enough to give some feel; and with the kingpin inboard, the brakes could sit further inboard, which left room for a deep dish. Rack and pinion steering transmits those forces, and the engineer's answer is to make the kingpin offset and the scrub radius as small as possible; the brakes, which have to fit inside the wheel, limit how far outboard the lower ball joint can go, and that pushed the spokes and the brakes outboard and flattened the outside of the wheel. He puts the change at about 20 years ago.
Wikipedia puts the effect on the steering in one line: the scrub radius "is changed whenever there is a change in wheel offset", and the greater it is, in either direction, the greater the steering effort (Wikipedia). So a wheel with a much lower offset than the original moves the geometry back towards what the engineers moved away from. How much that matters depends on the car and on how far the offset moves; we found no published measurement that gives a figure for a given dish.
How deep dish and concave wheels are made
The depth is a question of construction.
- One-piece (monoblock). The wheel is a single piece. On a one-piece wheel, a concave profile can be machined into the face. Onyx Forged's monoblock wheels are cut from a single block of forged aluminium and 5-axis CNC machined; the concave profile goes straight into the face, from flat to deep concave. See the monoblock range.
- Two-piece. A centre is assembled to a barrel. ISO 3911 calls a wheel of two main parts, held together by clamping bolts to form a rim with two fixed flanges, a divided wheel. Because the barrel is separate, width and offset no longer depend on the design of the face. On Onyx Forged's two-piece wheels, the centre is forged, the barrel is made to measure, the lip can be deep and the bolts remain visible.
- Three-piece. A forged centre sits between an outer and an inner barrel. It reaches extreme widths and a stepped lip, and it is made on quotation: see the three-piece construction.
You can tell a multi-piece wheel from its marking, where the maker follows the rule. UN Regulation No. 124 asks for the rim designation to carry "x" for a one-piece rim and "-" for a multi-piece rim, so 10J x 20 is one piece and 10J-20 is not (Regulation No. 124, § 5.1.2.1). Our guide to what size wheels fit my car reads the rest of the marking.
Do deep dish wheels weigh more?
A little, on the one set of published figures we found, and the difference is small. Enkei publishes a table for its RPF1, a cast wheel whose barrel is spun by its MAT process, with an "estimated weight" for each size and offset (Enkei). The column carries no unit; the page's text speaks of pounds, so we read pounds (a 17x8 at 16.05 is about 7.3 kg). In ten sizes the table lists the same wheel at two offsets with a weight at both, and in every one the wheel with the lower offset is the heavier, by 0.05 to 0.80:
| Size (PCD 5x114.3) | Lower offset | Higher offset | Difference |
|---|---|---|---|
| 16x7 | ET30: 14.30 | ET43: 13.70 | 0.60 (0.27 kg) |
| 17x9 | ET22: 16.35 | ET45: 15.65 | 0.70 (0.32 kg) |
| 17x9.5 | ET18: 16.75 | ET38: 16.25 | 0.50 (0.23 kg) |
| 17x10 | ET18: 17.25 | ET38: 16.90 | 0.35 (0.16 kg) |
| 18x9.5 | ET15: 18.20 | ET45: 17.40 | 0.80 (0.36 kg) |
Width counts for more over a larger range: on the same table a 17x7 ET45 is 14.90 and a 17x10 ET38 is 16.90, so three inches of width add about 2.0, or 0.9 kg, although the offset differs by 7 mm too. The table is not smooth (a 17x9 ET45 is listed lighter than a 17x8 ET45), which is why we call these estimates. They are one maker's figures for one design; another design will differ. What a few hundred grams per corner is worth is the subject of our guide to lightweight wheels and unsprung weight. Ask for the weight of one wheel at your size and offset, in kilograms, per wheel and not per set.
What the standards test
Two texts set the trials that a car wheel is run through, and the offset is in both of them. For the rotating bending fatigue trial, Japan's standard for light-alloy disc wheels, the one behind the JWL mark, sets a bending moment M = Sm × F × (μ × r + d), where F is the load for the tyre's maximum load capacity, r the loaded radius of the tyre, μ a friction coefficient of 0.7, Sm a factor of 1.5, and d the wheel's inset (positive), zeroset (zero) or outset (negative), in metres (MLIT, annex 2). UN Regulation No. 124 has the same shape, with other factors: Mb = S × Fv × (μ × rdyn + d), d being the inset in metres, μ 0.9 and S 2.0 in the schedule of its annex 6.
What follows is limited. A wheel is run at the moment its own offset, load rating and tyre produce, so a wheel with a low offset is not judged against the moment of an original wheel. That does not make a deep dish wheel stronger or weaker: the load rating and the geometry are the maker's, and the trial applies to that design. Whether a given wheel passes is a property of the wheel, not of the word "deep". Our guide to forged, cast and flow-formed wheels sets out what each trial does. Onyx Forged's wheels are designed to JWL/VIA standards, which means designed for the criteria of those trials; we do not claim a mark, nor a result for each wheel.
What to check on the car
A deep dish wheel usually has a low offset or a wide rim, or both. Everything in our guide to wheel offset applies, with larger numbers.
- The arch. The outer edge, and the tyre with it, moves outwards; on full lock and with the suspension compressed, the tyre moves towards the arch. In Great Britain a car must have wings or similar fittings to catch, so far as practicable, mud or water thrown up by the wheels (regulation 63(2)), and the MOT manual fails a tyre fouling a part of the vehicle, but only if it is fouling at the time of the test (MOT manual, 5.2.3). Our article on new forged wheels and the MOT sets out the rest.
- The track. Each millimetre taken off the ET adds two to the track over the axle.
- The brakes and suspension. The inner edge barely moves, but the shape of the inner spokes decides whether a large caliper clears. When UN Regulation No. 124 assesses a replacement wheel it asks as a rule for at least 3 mm to the brake components and 4 mm to suspension and steering components, in the worst case (Annex 10, § 2.1): assessment criteria, not a fitting instruction.
- The steering. See above: the scrub radius changes with the offset.
- A spacer is not a shortcut. A spacer behaves like a lower offset, and it adds a joint and longer fixings: see what a wheel spacer changes.
- Your insurer. The Financial Ombudsman Service lists changing alloy wheels as an example of a modification and advises telling the insurer as soon as possible (FOS).
What to ask a seller
- The width and the offset of each wheel, front and rear, in millimetres, and the depth you will see.
- The construction: one piece, two pieces or three, and which parts are forged.
- The weight of one wheel at that size, in kilograms.
- The load rating and the marks the wheel carries, with who applied them.
- The PCD and the centre bore for your exact car, so that no ring or spacer is needed.
- A written statement that the wheel fits your exact version of the car, and what it is based on.
How Onyx Forged does it
You are not asked for a depth, an offset, a width or a PCD: they follow from your car. You tell us the car and how you want the wheels to sit. The Onyx Forged design office works the numbers out for the car as you described it (brakes, suspension, bodywork) and checks them with you before anything goes into production; customer service sends you, on request, the width, diameter and offset of each wheel. We do not give a customer an offset or a depth to pick: a figure only means something for one car, with its brakes, ride height and tyres. A different tyre or ride height can change the result, so say so.
Frequently asked questions
What does deep dish mean on wheels?
The mounting face of the wheel sits far inside the outer lip, so the lip stands out from the spokes. The nominal depth is half the width minus the offset.
What is the difference between deep dish and concave?
Deep dish is about where the face sits (width and offset); concave is about the shape of the face (spokes that curve inwards). A wheel can be one without being much of the other.
How do you measure the depth of a dish?
From the width and the offset: width ÷ 2 − ET, in millimetres, gives the most the dish can be. A straightedge across the lip and a measurement down to the face gives the visible depth, which is the nominal one minus how far the spokes stand out from the mounting face.
Are deep dish wheels heavier?
Slightly, on one maker's published figures: the lower-offset version of the same size was heavier in all ten sizes, by 0.05 to 0.80 on wheels of 14 to 18 inches. Width adds more than offset does.
Are deep dish wheels legal in the UK?
No text we read bans them. The wheel has to be covered by the wing, so far as practicable, and a tyre fouling a part of the car at the time of the MOT is a major defect.
Do deep dish wheels need a low offset?
A low offset or a wide rim, or both: either puts the face further inside the lip.
Can a monoblock be deep dish?
A one-piece wheel can have a deep concave profile; Onyx Forged's monoblock page describes the profile as machined from flat to deep concave. Two-piece and three-piece wheels are the constructions built for deep lips and extreme widths, because the barrel is a separate part.
Do deep dish wheels change the handling?
Through the offset and the width, which change the track and the scrub radius, not through the dish itself. We found no published test that measures the effect of a given depth.
Where to go next
For the arithmetic of where a wheel sits, read wheel offset; for finding which sizes your car lists, what size wheels fit my car; for what the weight of a wheel changes, lightweight wheels and unsprung weight. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards, in monoblock, two-piece and three-piece construction: see Onyx Forged and the catalogue.
Sources
- UN Regulation No. 124, replacement wheels: §§ 2.6 and 5.1.2.1, Annex 6 and Annex 10 § 2.1; MLIT, annex 2 (in Japanese); ISO 3911:2021 (free preview).
- Porsche bulletin 911 (992) 38/25; Tesla Model 3 service manual 2024+; Audi Original Zubehör, winter wheel 10.5Jx22.
- Enkei, RPF1 specification (estimated weights).
- The Autopian, Huibert Mees, why car wheels are so flat (13 September 2022, re-published 1 April 2024); Wikipedia, Scrub radius.
- GOV.UK, MOT inspection manual, section 5; The Road Vehicles (Construction and Use) Regulations 1986, regulation 63; Financial Ombudsman Service, car modifications and insurance (1 October 2024).
- NIST SP 811, appendix B.9, conversion factors.
All pages were read on 15 October 2026.
The Onyx Forged design office.