ET disc offset: what is it and why is it important for your car

Have you ever paid attention to the markings on the inside of a wheel rim? Among the numbers and letters you will definitely find an abbreviation ET with a numeric value - for example, ET45 or ET30. This option, which many car owners ignore when purchasing wheels, is actually critical to the safety and longevity of your car. An incorrect offset can turn even the nicest, lightest wheels into a source of ongoing problems, from uneven tire wear to suspension failure.

In this article we will look at what it is ET-disk crash, how it is measured, what it affects and why car manufacturers regulate its values so strictly. You will find out whether it is possible to install wheels with a different offset than the factory recommends, what consequences this will entail, and how to measure ET yourself if the markings have been erased. And at the end there is a table of permissible offsets for popular car models and answers to frequently asked questions.

What is ET disk ejection: a simple explanation

ET (from German EinpressTiefe) is the distance between disk mating plane (the part that presses against the car hub) and imaginary central plane of the disk. It is measured in millimeters and can be:

• 🔹 Positive (for example, ET45) - the mating plane is shifted outward relative to the center of the disk.
• 🔹 Zero (ET0) - the planes coincide.
• 🔹 Negative (for example, ET-15) - the mating plane is recessed inward relative to the center.

Simply put, ET determines how deep the disc sits on the hub. If the overhang is too large (for example, ET50 instead of recommended ET35), the wheel will be “recessed” inside the arch. If it's too small (ET20 instead of ET45)—the wheel will move outward, which can lead to contact with the wheel arch liners or suspension elements.

It is important to understand that ET is not a universal parameter. It is calculated by the car manufacturer taking into account:

• 🔧 Suspension designs (MacPherson strut, multi-link, etc.).
• 🔧 Wheel arch widths and gaps to body elements.
• 🔧 Loads on wheel bearings and levers.
• 🔧 Steering kinematics (especially for the front axle).

How ET Departure Affects a Vehicle: 5 Key Consequences

Failure to comply with the disc offset to factory recommendations leads to a number of problems that appear both immediately after installation and after several thousand kilometers. Let's consider the main consequences:

⚠️ Attention: Even if discs with non-standard ET physically fit onto the hub and do not catch the arches, this does not mean that they are safe. Violation of the wheel geometry changes the vectors of forces acting on the suspension, which leads to accelerated wear.

1. Change in load on wheel bearings

When increasing the reach (for example, instead of ET35 set ET45) the wheel moves closer to the center of the car. It increases force application shoulder, due to which a greater bending moment acts on the bearing. The result is overheating, backlash and failure after 10–20 thousand km instead of the required 100+ thousand km.

2. Uneven tire wear

Wrong ET changes wheel alignment, even if it was adjusted on the bench. For example, with a reduced offset (ET20 instead of ET40) the top of the wheel tilts outward, which leads to intense wear on the outer edge of the tread. With increased overhang, the inner edge suffers.

3. Deterioration in controllability

The car becomes less responsive to steering inputs, especially at high speeds. The reason is the displacement wheel center of mass relative to the axis of rotation. In critical situations (avoiding an obstacle), this can lead to loss of control.

4. Increased load on suspension elements

Levers, ball joints and shock absorbers begin to work in off-design modes. For example, with negative ET (ET-10) suspension arms experience additional torsional loads, which leads to their deformation or breakage.

5. Risk of damage to the body and suspension

If a disc with an abnormal offset catches on the arch or suspension elements when turning or on uneven surfaces, this leads to:

• 🚗 Scratches and dents on the fender liners.
• 🚗 Damage to CV joint anthers.
• 🚗 Deformation of the anti-roll bar.

What happens if you install wheels with ET 5–10 mm different from the standard one?

Even a small deviation (for example, ET42 instead of ET45) leads to:

- Increase the load on the wheel bearing by 15–20%.

- Displacement of the tire contact patch with the road, which impairs grip on wet surfaces.

- Possible imbalance of braking forces (if the offset is different on the front and rear axles).

How to measure ET offset yourself: step-by-step instructions

If the markings on the disc have worn off or you buy used discs without documents, you can measure the offset yourself. You will need:

• 📏 Ruler or caliper (preferably digital).
• 📐 Square (or any object with a right angle).
• 🧲 Magnet (to search for the mating plane).

1. Place the disc on a flat surface with the outer side down

2. Place the square against the mating plane (where the disc presses against the hub)

3. Measure the distance from the plane of the square to the inner edge of the disk (parameter A)

4. Turn the disk over and measure the distance from the plane of the square to the outer edge (parameter B)

5. Calculate ET using the formula: ET = (A + B)/2 – B

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Calculation example:

Let's say you measured:

• A (inner edge) = 120 mm,
• B (outer edge) = 50 mm.

Then ET = (120 + 50)/2 – 50 = 85 – 50 = 35 mm.

For accuracy, repeat measurements at 3-4 points around the circumference of the disk. The permissible deviation between measurements is no more than 1 mm. If the spread is greater, the disc is deformed and unsuitable for use.

ET tolerances: when to deviate from factory recommendations

Car manufacturers always indicate nominal ET for each model. However, in some cases slight deviations are allowed. Let's consider when this is possible and when it is strictly prohibited.

Situation	Tolerance ET	Terms	Risks
Installing discs of different widths	±3 mm	Wheel width differs by ±1 inch from standard	Minimum if other parameters are met
Tuning (wheel arch extension)	±5–10 mm	Arches modified, suspension strengthened	Increased bearing wear
Replacing disks with a winter set	±2 mm	Tires narrower than standard ones by 5–10 mm	Uneven tread wear
Off-road operation	±5 mm (downward)	Reinforced levers and bearings installed	Deterioration in handling on asphalt

Critical rule: on the front axle, the ET deviation should be minimal (no more than ±2 mm), since it is the most loaded and responsible for handling. A slightly larger spread is allowed on the rear axle, but not more than ±5 mm for most passenger cars.

Exceptions:

• 🔧 Cars with multi-link suspension (for example, BMW 5 Series, Mercedes E-Class) are more sensitive to changes in ET due to complex kinematics.
• 🔧 All-wheel drive crossovers (for example, Toyota RAV4, Subaru Forester) allow slightly greater spread due to the larger wheel arches.

ET offset for popular car brands: compatibility table

Below is a table with ET ratings for popular models. Please note: the data is valid for basic versions with factory rim sizes. For sports modifications (for example, Volkswagen Golf GTI or BMW M3) and cars with packages Off-Road values may vary.

Make and model	Year of manufacture	Standard disk size	Recommended ET, mm	Permissible range ET, mm
Volkswagen Polo	2018–2026	6Jx15, 6.5Jx16	45–48	43–50
Toyota Camry	2017–2026	7Jx17, 7.5Jx18	40–45	38–47
Hyundai Solaris	2020–2026	6Jx15, 6.5Jx16	46–49	44–51
Kia Sportage	2016–2026	7Jx17, 7.5Jx18	38–42	35–45
Lada Vesta	2015–2026	6Jx15, 6.5Jx16	40–45	38–47

For an accurate selection of discs, always check with instruction manual your car or use online catalogs of wheel manufacturers (for example, BBS, OZ Racing, Kosei). Please note that some models have different ET values for the front and rear axles (e.g. Porsche 911 or Audi Quattro).

Common mistakes when choosing ET disks and how to avoid them

Many car owners encounter problems after installing wheels with abnormal offset, even if they look suitable on the outside. Let's look at typical mistakes and their consequences:

1. Buying disks “by appearance”

Often drivers choose wheels based only on design and diameter, ignoring ET. For example, on Skoda Octavia with factory ET45 install disks with ET35, because they “protrude more beautifully from the arch.” The result is that after 10 thousand km you have to change the wheel bearings and levers.

2. Using spacers to “adjust” ET

Some “masters” offer to compensate for incorrect overhang using spacers (metal rings between the disc and the hub). This is dangerous for two reasons:

• 🔴 Spacers increase the load on the hub bolts, which can lead to their breakage.
• 🔴 Even high-quality spacers shift the center of mass of the wheel, worsening balance.

⚠️ Attention: Spacers with a thickness of more than 5 mm are strictly prohibited for use on public roads. In most countries (including Russia) this is regarded as a malfunction for which a fine is imposed.

3. Ignoring ET difference between front and rear axle

On many vehicles (especially those with all-wheel drive), the offset on the front and rear axles is different. For example, at Subaru Impreza front ET may be 50, and the rear one - 45. If you install the same discs, this will lead to an imbalance in handling.

4. Buying discs “for growth”

Some car owners buy wheels with extra width (for example, 8J instead of 7J), hoping to install wider tires in the future. However, this often does not take into account that wide disks require smaller ETso that the wheel does not catch on the arch. As a result, a disk with ET45, suitable for 7J, will have an effective offset ET35–40 for 8J, which will cause problems.

FAQ: Frequently asked questions about ET disk failure

Is it possible to install rims with ET that are 5 mm smaller than the factory ones?

Technically it is possible, but this will lead to:

• Increased load on wheel bearings by ~20%.
• Displacement of the tire contact patch, which will worsen handling at high speeds.
• Possible wheel hitting the arch when the vehicle is fully loaded.

If you still decide to reduce ET, be sure to:

• Check the clearances between the tire and the suspension/body elements at maximum steering angle.
• Install reinforced wheel bearings (eg SKF or FAG).
• Check your wheel alignment more often (every 10 thousand km).

Which ET is better for lowered suspension?

When lowering a car, it is recommended:

• Increase ET 3–5 mm relative to the standard one, so that the wheel “sinks” into the arch and does not catch on the fender liners.
• Use discs with smaller width (for example, 7J instead of 8J) to reduce the risk of contact with the arch.
• Choose tires from low profile, but not less than 40% of the width (for example, 205/40 R17).

Example: for Volkswagen Golf lowered by 40 mm and standard ET 45 will be optimal ET48–50.

Does ET affect fuel consumption?

Yes, but indirectly. Incorrect offset increases:

• Rolling resistance due to changes in wheel alignment angle.
• Suspension load, which causes the engine to spend more energy overcoming friction.
• Aerodynamic dragif the wheels protrude beyond the dimensions of the body.

According to our measurements, a deviation of ET by ±10 mm from the standard one increases fuel consumption by 0.3–0.5 l/100 km.

Is it possible to drive on wheels with different ET on the same axle?

Absolutely not. Different offsets on the same axle lead to:

• Uneven distribution of braking forces (the car may pull to the side when braking).
• Different loads on the wheel bearings, which will lead to their accelerated wear.
• Unstable handling, especially at high speeds (yaw effect).

The permissible difference in ET between wheels on the same axle is no more than 1 mm.

How is ET related to wheel alignment?

ET directly affects camber (wheel tilt in the vertical plane):

• Decreased ET (disc protrudes outwards) → positive camber (the top of the wheel is inclined outward).
• Increase ET (disc recessed inward) → negative camber (the top of the wheel is inclined inward).

Toe (tilt in the horizontal plane) changes less, but if the ET is too off, adjustments may be necessary.

Example: on Honda Civic with factory ET 45 installing disks with ET35 will lead to an increase in camber by ~0.5°, which will cause intense wear on the outer edge of the tire.