Disc offset ET: what the marking means, how to measure and why it is safety critical

Choosing rims is a task where there are no trifles. Even millimeter parameter deviation departure (ET) can turn a comfortable ride into a nightmare: from vibrations on the steering wheel to accelerated wear of wheel bearings. But if car owners still somehow understand the diameter and width of the disk, then the offset marking often remains a “dark forest”. Meanwhile, it is this parameter that determines how much the disc will be “recessed” into the arch or, conversely, protrude outward - and this directly affects the handling and life of the chassis.

In this article we will not just explain what it is ET on disks and how to decrypt it. We will show you why car manufacturers regulate this parameter so strictly, the dangers of installing wheels with the wrong offset (spoiler: it's not just aesthetics!), and how to measure ET yourself if the markings have been erased. We’ll also debunk the myths about “permissible deviations” and explain why even +5 mm can result in expensive repairs.

What is rim offset (ET) and why is it important?

Disc offset (indicated as ET from German EinpressTiefe - “pressing depth”) is the distance between disk mating plane (the one that presses against the hub) and imaginary center line of the rim. It is measured in millimeters and can be:

• 🔹 Positive (ET35, ET40) - the mating plane is shifted to the outer side of the disk (the disk is “recessed” into the arch).
• 🔹 Zero (ET0) - the plane coincides with the center line.
• 🔹 Negative (ET-15) - the plane is shifted inward, the disk protrudes outward (“tuning” version).

Why is this necessary? Departure determines load on wheel bearings and suspension elements. If the disk “sticks out” too much or, conversely, is “recessed”, the shoulder of force application changes - and this leads to:

• 🔧 Accelerated wear of bearings (2-3 times faster than normal!).
• 🔧 Uneven wear of tires (even with correct wheel alignment).
• 🔧 Deterioration of controllability at high speeds (the car “scours”).

Auto manufacturers calculate ET taking into account machine weight, suspension type and wheel loads. For example, at Volkswagen Golf VII standard offset is ET45, and BMW 3 Series (G20) — ET30. A deviation of even ±5 mm can cause the wheel to touch the arch when fully loaded or on bumps.

How to read departure markings on a disk: examples and explanation

Each disc has a marking stamped on it, where, among other parameters (diameter, width, PCD), the offset is indicated. It looks like this:

7.5J x 16 H2 5x112 ET45 D57.1

In this example ET45 - and there is a departure. But how do you know if it suits your car?

Marking	Decoding	Example car
ET30	Overhang 30 mm (positive)	Audi A4 B9, BMW 5 Series (G30)
ET42	Reach 42 mm (standard for many “folk” cars)	Skoda Octavia, Hyundai Tucson
ET0	Zero departure	Tuning wheels for Nissan GT-R, Toyota Supra
ET-15	Negative offset (-15 mm)	SUVs (Jeep Wrangler), wide rims for Mercedes AMG

⚠️ Attention: If there is no obvious marking on the disc ET, look for alternative notations:

• 🔹 Offset - English equivalent (for example, Offset: +45).
• 🔹 Deport - in French catalogues.
• 🔹 Just a number with a “+” or “-” sign (for example, +38).

Consequences of an incorrect departure: from vibrations to accidents

Many car owners believe that “a couple of millimeters here and there is not a big deal.” This is a dangerous misconception. Let's look at what deviation from the standard ET leads to:

⚠️ Attention: Installing discs with offset ET35 instead of ET45 (10 mm difference) increases the load on the wheel bearing by 20–30%. When driving on bad roads, this reduces its resource from 100,000 km to 30,000–40,000 km!

Consequences depending on the deviation:

• 🔴 ET is less than standard (the disk protrudes outwards):
  • ✔ The wheel “sticks out” from the arch (it can hit the wheel arch liners when turning).
  • ✔ The load on external bearings and suspension arms increases.
  • ✔ Risk of the wheel “falling off” from the hub during emergency braking (due to a shifted center of gravity).
• 🔴 ET is larger than standard (the disk is “recessed”):
  • ✔ The wheel touches internal elements (shock absorber, spring).
  • ✔ The track decreases - the car “holds” the road worse at speed.
  • ✔ Rapid wear of the inner edge of the tire.

Case Study: Owner Kia Sportage I installed wheels with ET38 instead of the standard ET42. After 10,000 km, a bearing noise appeared, and after 20,000 km, a crack appeared in the suspension arm. The repair cost 45,000 rubles.

Real case from the service

What happened to the Toyota RAV4 after installing rims with ET20 instead of ET35:

After 5,000 km the following appeared:

• ✔ Steering wheel vibration at speeds of 100+ km/h.
• ✔ Play in the front suspension (diagnostics showed wear of the silent blocks).
• ✔ Uneven tire wear (“saw” along the inner edge).

It was possible to return everything back to normal only after replacing the disks with standard ones and repeating the wheel alignment (cost: 28,000 rubles).

How to measure disc offset yourself (3 ways)

If the markings have worn off or you are buying used wheels, you can measure ET yourself. You will need:

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

Method 1. Classic (with a ruler)

1. 1. Place the disc on a flat surface face down.
2. 2. Place the ruler with its edge against the rim of the disc (perpendicular).
3. 3. Measure the distance from the surface to the mating plane (A).
4. 4. Turn the disk over, repeat the measurement (B).
5. 5. Departure ET = (B – A) / 2.

Method 2. With a square (more precisely)

Attach the square to the rim so that one side touches the mating plane, and the other touches the inner edge of the disk. Measure the distance from the square to the outer edge - this will be ET (if the disk is symmetrical).

Method 3. According to the formula (for complex disks)

If the disk has an asymmetrical shape, use the formula:

ET = X – Y / 2

where:

• X — distance from the mating plane to the inner edge.
• Y — total width of the disk.

Permissible departure deviations: myths and reality

There is often advice on the Internet: “you can deviate from the standard ET by ±5 mm.” This dangerous simplification. The permissible deviation depends on:

• 🔹 Suspension type (McPherson, multi-link).
• 🔹 Vehicle weights (for Mercedes S-Class and Daewoo Matiz standards are different!).
• 🔹 Disc width (the wider, the stricter the requirements for ET).

Car type	Max. permissible deviation ET	Note
Cars (sedan, hatchback)	±3 mm	For VW, Toyota, Hyundai — no more than ±2 mm!
Crossovers/SUV	±5 mm	But only when the gauge increases (ET is less than standard).
Sports cars	±1 mm	Even the slightest deviation affects controllability.

⚠️ Attention: Manufacturers BMW and Audi officially prohibit any deviations from the standard ET. The manuals state: “The use of discs with inappropriate offset will void the suspension warranty.”

Example: for Ford Focus III standard ET - 50 mm. Installing discs with ET45 (5 mm difference) will result in:

• 🔹 Shift the wheel outward by 5 mm on each side → the track will increase by 10 mm.
• 🔹 Increased load on steering rods and silent blocks.
• 🔹 Risk of the wheel hitting the fender liner when fully loaded.

How to choose wheels by offset: step-by-step instructions

To avoid making a mistake with your choice, follow this algorithm:

1. 📋 Find out the standard ET for your car.
   • Look in the manual, on a sticker in the doorway or on the manufacturer's website.
   • Example: for Skoda Octavia A7 — ET45, for Renault Duster — ET50.
2. 🔍 Check the markings on the disc.
   • ET must match the standard up to a millimeter (for most cars).
   • If there are multiple values on the disk (for example, ET35/40), take the one that is closer to the standard one.
3. ⚖️ Compare with other parameters.
   • Disc width (J) and diameter (R) must comply with the manufacturer's recommendations.
   • PCD (bolt pattern) - no deviations! For example, 5x112 not compatible with 5x114.3.

🛒 Buy only from trusted sellers.

• There are many fakes on the market that are mislabelled as ET.
• Ask for a certificate of conformity or a disk passport.

Example of correct selection: for Toyota Camry XV70 standard parameters:

• 🔹 Size: 7.5J x 17.
• 🔹Departure: ET45.
• 🔹 PCD: 5x114.3.

Disk with parameters 8J x 17 ET40 5x114.3 doesn't fit, despite the coincidence of PCD and diameter!

Frequently asked questions about disc failure (FAQ)

❓ Is it possible to install wheels with ET0 on a regular car (for example, VW Polo)?

No. Wheels with zero or negative offset are designed for sports cars with a wide track. On VW Polo (standard ET45–50) this will lead to:

• 🔹 Wheels sticking out beyond the arches (you may have to cut off the wheel arches).
• 🔹 Excessive load on wheel bearings (the resource will be reduced by 3-4 times).
• 🔹 Failure to pass technical inspection (due to non-compliance with the design).

❓ What to do if you bought discs with the wrong ET?

Solutions options:

1. 🔄 Return the discs to the seller (if the receipt is saved and the markings are not broken).
2. 🔧 Use spacers (but this is a half-measure, since it shifts the center of gravity of the wheel).
3. 🚗 Sell the discs and buy the right ones (the most reliable way).

⚠️ Spacers with a thickness of more than 10 mm require hub re-drilling - it's unsafe!

❓ Does offset affect wheel alignment?

Yes, but indirectly. ET itself does not change wheel alignment, but:

• 🔹 Incorrect offset displaces wheel center relative to the axis of rotation.
• 🔹 This may lead to uneven tire wear, even if the wheel alignment is done correctly.
• 🔹 On a car with a rear multi-link suspension (for example, Audi A6) incorrect ET violates suspension kinematics.

After replacing disks necessarily check the wheel alignment after 500–1000 km.

❓ Why does one car have different standard offsets for different engines?

This is due to weight distribution and suspension settings. For example:

• 🔹 Volkswagen Passat B8 with the 1.4 TSI engine it has ET45, and the 2.0 TDI version has ET42.
• 🔹 BMW 3 Series (G20) in the basic configuration: ET30, and in M package — ET25 (due to wider wheels).

The manufacturer calculates ET taking into account:

• 🔹 Engine weight (diesel is heavier than gasoline).
• 🔹 Suspension stiffness (sports versions have different settings).
• 🔹 Tire widths (the wider the tires, the more important the exact offset).

❓ Is it possible to drive on wheels with ET 2-3 mm larger/smaller than standard?

Technically yes, but with caveats:

• 🔹 For passenger cars (weight up to 1.5 t) deviation ±2 mm is usually not critical, but reduces the service life of the suspension.
• 🔹 For crossovers (weight 1.8–2.5 t) even ±2 mm can cause vibrations at speeds of 120+ km/h.
• 🔹 On sports cars (for example, Golf GTI) a deviation of 1 mm is already felt on the steering wheel.

🔴 Absolutely unacceptable deviation for cars with:

• 🔹 Adaptive suspension (Audi Magnetic Ride, BMW Adaptive Suspension).
• 🔹 All-wheel drive (changes in ET affect the geometry of the drive shafts).