What is wheel offset (ET)? Positive, zero and negative

In short. Wheel offset, written ET on the wheel (from the German Einpresstiefe, "insertion depth"), is the distance in millimetres between the wheel's mounting face and the centre line of its rim. The mounting face is the flat surface at the back of the wheel that sits against the hub; the centre line is the plane that cuts the rim into two halves of equal width. Positive offset (ET45, say) puts the mounting face towards the outside of the wheel, so the wheel sits further in under the arch. Zero offset (ET0) puts it on the centre line. Negative offset (ET-20) puts it towards the inside of the wheel, so the wheel sits further out, which is where the word "poke" comes from. For two wheels of the same width, every millimetre taken off the ET moves the wheel one millimetre outwards, and every millimetre added moves it one millimetre inwards. To compare two wheels with their widths, use our wheel offset calculator; the rest of this page explains the numbers behind it.

What ET means, and who defines it

The hub does not move. The wheel is placed around it, so shifting the mounting face inside the wheel shifts the whole wheel in the arch. That is all offset is.

Two official texts define the measurement. UN Regulation No. 124, which covers replacement wheels for passenger cars, calls it the inset: the distance from the attachment face of the disc to the centre line of the rim, which can be positive, zero or negative (§ 2.6). It also requires the inset to be marked on the wheel (§ 5.1.3); its marking example reads "a wheel inset of 36 mm". Japan's technical standard for light-alloy disc wheels, the standard behind the JWL mark, defines it in the same way, as inset (+), zero set (0) or outset (-), measured between the vehicle mounting face and the rim centre line (MLIT, annex 2).

So "offset", "ET", "inset" and "rim offset" (the term Porsche uses, RO) are one measurement. The sign is the same everywhere: positive when the mounting face is on the outer side of the centre line.

What the original offsets of recent cars look like

The original-equipment (OE) wheels we have recorded are all positive-offset wheels. We have recorded the offsets that manufacturers and their parts catalogues publish for 17 recent car generations (BMW M, Audi RS, Porsche, Tesla, Mercedes G-Class and Volkswagen Golf), and they run from ET19 to ET81. None is zero or negative. Three of them, read in the manufacturer's own document:

The same car often has a different offset and width front and rear: the Tesla's rear wheel is an inch wider than its front one and has an ET 11 mm higher. That is not a quirk of one maker; it is the point of offset. It places each wheel where the car has room for it.

How to find the offset of a wheel

• On the wheel. It is marked, in millimetres, on the back of a spoke or near the mounting face, as ET followed by the number (ET45). Some makers write it after the size: 8.5J x 19 ET45.
• For original wheels, in the owner's manual, the manufacturer's wheel and tyre list, or the parts catalogue. The tables above come from those.
• For a wheel with no marking, by measuring it, as below.

American catalogues often give backspacing instead of offset, in inches. It describes the same geometry from the other side, which is why it is easy to turn one into the other.

How to measure offset from backspacing

On a wheel taken off the car, with no tyre, you need two measurements and a straightedge:

1. Overall width: from the outer edge of one lip to the outer edge of the other. It is larger than the nominal width printed on the wheel, which is taken between the flanges, by roughly an inch (25 mm). Measure it rather than assuming.
2. Backspacing: lay the straightedge across the back of the wheel, resting on the inner lip, and measure down to the mounting face.
3. Calculate: offset = backspacing minus the distance from the inner lip to the centre line. The centre line is half way between the faces of the two flanges, so that distance is half the nominal width plus the thickness of the inboard flange. Half the overall width is a close approximation: the error is half the difference between the thicknesses of the two flanges, a millimetre or two. If the result is negative, the offset is negative.

Example in millimetres. Overall width 240 mm, backspacing 165 mm. The centre line is about 120 mm from the inner lip and the mounting face is 165 mm from it, so the face is about 45 mm beyond the centre line: ET45.

Example in inches. A 9.5J wheel has an overall width of about 10.5 inches, or 266.7 mm, so its centre line is about 133.35 mm from the inner lip. Backspacing of 6.6 inches is 167.6 mm. The offset is 167.6 minus 133.35, or about ET34. The reverse also works: a wheel of ET35 on that width has a backspacing of about 133.35 + 35 = 168.35 mm, or 6.63 inches.

An inch is exactly 25.4 mm (NIST), so there is no rounding in the conversion, only in the measurements.

How far does a change move the wheel?

Measure from the mounting face, which stays where the hub puts it. The outer edge of the rim is then half the width minus the ET away from the face, and the inner edge is half the width plus the ET:

• outer edge = width ÷ 2 − ET
• inner edge = width ÷ 2 + ET

(Widths in millimetres; one inch of width is 25.4 mm. The positions are taken between the flanges, where the width is printed, so the differences between two wheels are exact even though the edges are not the outermost part of the lip.)

A quick offset chart. Taking ET45 as the reference (any other would do), this is where a wheel of the same width sits for each offset:

Example 1: 8J x 19 ET45 against 9J x 19 ET35. The 8J is 203.2 mm wide, so half of it is 101.6 mm; the 9J is 228.6 mm, half 114.3 mm.

• Outer edge: 101.6 − 45 = 56.6 mm, against 114.3 − 35 = 79.3 mm. The wheel comes out by 22.7 mm.
• Inner edge: 101.6 + 45 = 146.6 mm, against 114.3 + 35 = 149.3 mm. It moves 2.7 mm towards the suspension.
• The centre line moves out by the difference in ET, 10 mm, so the track width grows by 20 mm over the axle.

Example 2: the Tesla Model 3 above. At the front, a 9J wheel (114.3 mm) with ET34 has its outer edge 80.3 mm from the face and its inner edge 148.3 mm. At the rear, a 10J wheel (127 mm) with ET45 has an outer edge 82 mm from the face and an inner edge 172 mm. The two outer edges are within 2 mm of each other, while the rear wheel's extra inch of width has gone almost entirely inwards, towards the suspension.

Our wheel offset calculator does this arithmetic for any two wheels and shows the change on each side. It compares; it does not tell you whether the wheel will clear your car.

Spacers

A spacer fitted between the hub and the wheel moves the wheel out by its thickness, exactly as if the ET were lowered by that amount: a 10 mm spacer on an ET45 wheel puts it where an ET35 wheel would sit. It does not change the wheel. It lengthens the lever acting on the hub, and the wheel studs or bolts must still engage the hub by the length the manufacturer requires. Onyx Forged wheels are designed to be fitted without spacers.

What offset changes on the road

• Clearance on both sides. Lowering the ET brings the outer edge and the tyre towards the arch and moves the inner side away from the suspension, steering and brake parts; raising it does the opposite. A wider wheel at the same ET goes both ways at once.
• Track width. Each millimetre of ET is two millimetres of track over an axle, because there is a wheel on each side.
• Steering. The scrub radius is the distance, seen from the front of the car, between the steering axis and the centre of the tyre's contact patch. It "is changed whenever there is a change in wheel offset", and the greater it is, in either direction, the greater the steering effort (Wikipedia). The effect grows with the size of the change.

Why a wheel rubs, and how small the gaps are

A wheel has two neighbours. On the outside it is the arch: when the suspension compresses or the wheel is on full lock, the tyre moves towards it. On the inside it is the suspension, the steering and the brake caliper. When UN Regulation No. 124 assesses a replacement wheel, it asks, as a rule, for a clearance of at least 3 mm to the brake components and 4 mm to suspension and steering components, in the worst case (Annex 10, § 2.1). These are criteria for assessing a wheel, not an instruction for fitting one, but they show the scale: millimetres.

The caliper is not settled by offset alone. Two wheels of the same diameter and ET can clear a large caliper or not depending on the profile of their spokes on the inner side. A wider or more rounded tyre also reaches further into the arch than a narrower one on the same wheel.

Is there a permitted tolerance?

No text sets a tolerance in offset that is valid for every car. Several UK pages quote a "2 per cent" allowance and apply it to the wheelbase, without a source; a change of offset moves the track, not the wheelbase. What matters is what the car itself allows: nothing touching with the wheel on full lock and the suspension compressed, and the wheel still covered by the bodywork.

In Great Britain, two official texts bear on that:

• The MOT. The inspection manual fails a tyre fouling a part of the vehicle (a major defect), but only if it is fouling at the time of the test: contact caused by flexing or suspension movement is not a defect. It also fails a wheel and its fixings that are not compatible (major) and a wheel with a fracture (dangerous). Sections 5 and 6 of the manual have no item that measures how far a wheel sits out of the arch (MOT inspection manual, section 5). Our article on new forged wheels and the MOT sets out the rest of what the tester checks.
• The Construction and Use Regulations. A car must have wings "to catch, so far as practicable, mud or water thrown up by the rotation of its wheels" (regulation 63(2), which applies in England, Wales and Scotland). A wheel that sits out far enough to defeat that purpose is a risk to check before you fit it.

Changing the wheels is also a modification for your insurer: the Financial Ombudsman Service lists changing alloy wheels as an example, and advises telling the insurer as soon as possible (FOS).

Common mistakes

• Reading the sign backwards. A bigger ET tucks the wheel in; a smaller ET pushes it out. ET is not a depth measured from the outside edge.
• Comparing ET without width. At the same ET, a wider wheel goes out on one side and in on the other, by half the difference in width each time.
• Forgetting the spacer. A spacer behaves like a smaller ET by its thickness.
• Copying another car's offset. The same PCD does not mean the same offset: hub, track, brakes and arches differ between models, and sometimes between versions of one model.
• Forgetting the rear axle. As the Tesla shows, front and rear often differ.

How offset is settled at Onyx Forged

We do not give a customer an offset to pick, and we do not suggest one in conversation: a figure only means something for one car, with its brakes, its ride height and its tyres. You tell us the car and how you want the wheels to sit. You are not asked for the offset (ET), the PCD (bolt pattern) or the width: they follow from your car. The Onyx Forged design office works them 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. A different tyre or ride height can change the result, so say so when you describe the car.

Frequently asked questions

What does ET mean on a wheel?

It is the offset, in millimetres, from the German Einpresstiefe. ET35 means the mounting face is 35 mm on the outer side of the rim's centre line.

Which sticks out more, ET35 or ET45?

ET35. At the same width it puts the wheel 10 mm further out than ET45 and widens the track by 20 mm over the axle.

Is a higher or lower ET better?

Neither is better in itself. The right offset is the one that fits your car's arches, suspension and brakes; for that, the car's own documents are the reference.

Is offset the same as backspacing?

No, but they are linked. Backspacing is the distance from the mounting face to the inner lip, usually in inches; offset is the distance from the mounting face to the centre line, in millimetres. Offset equals backspacing minus the distance from the inner lip to the centre line, which is about half the overall width.

Can the offset of a wheel be changed?

Not on a wheel that exists: it is fixed when the wheel is made. A spacer moves the wheel the same way, without changing the wheel; for another offset you need another wheel.

What is a negative offset?

One where the mounting face is on the inner side of the centre line, so the wheel sits further out. The original wheels of the recent cars we have recorded are all positive.

Does offset affect the tyre size I can fit?

Not directly. Width, diameter and tyre size fix the tyre's own dimensions; the offset only decides where that wheel and tyre sit. Our guide to reading a tyre size explains the tyre side.

Where to go next

PCD and centre bore decide whether a wheel can be bolted on at all: PCD, bolt pattern and centre bore. Forged, cast and flow-formed wheels differ in how they are made: what actually differs. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards: see Onyx Forged and the catalogue.

Sources

• UN Regulation No. 124, replacement wheels: § 2.6, § 5.1.3, Annex 3 and Annex 10 § 2.1.
• MLIT, annex 2, technical standard for light-alloy disc wheels (7 July 2008).
• GOV.UK, MOT inspection manual, sections 5.2.2 and 5.2.3.
• The Road Vehicles (Construction and Use) Regulations 1986, regulation 63.
• Financial Ombudsman Service, car modifications and insurance (1 October 2024).
• Tesla Model 3 service manual 2024+, Wheels; Porsche bulletin 911 (992) 38/25; Audi Original Zubehör, winter wheel 10.5Jx22.
• Wikipedia, Scrub radius; NIST SP 811, appendix B.9, conversion factors.

All pages were read on 15 October 2026.

The Onyx Forged design office.