ET disk failure - what is it and why can’t it be ignored?

Have you ever heard a tire mechanic say: “These wheels have the wrong offset"? Or did you notice that after changing the wheels, the car began to “walk” on the road, and the steering wheel began to vibrate at speed? In 90% of cases it is the fault disc offset ET - a parameter that many car owners ignore when buying new wheels. Meanwhile, incorrect ET can not only degrade handling, but also lead to premature wear of the suspension or even emergency situation on the road.

In this article we will look at what is hidden behind the abbreviation ET, how offset affects the behavior of a car, and why manufacturers regulate its values so strictly. You will find out whether it is possible to install wheels with a different offset, how to measure it correctly, and what to do if there are simply no suitable wheels in the store. Without complex formulas and abstruse terms - only practical advice for those who want to drive safely and comfortably.

What is disk ejection ET: simple about the complex

Disc offset (indicated as ET from German EinpressTiefe - “pressing depth”) is the distance between disk mating plane (the part that presses against the hub) and imaginary central plane of the rim. Simply put, this is an indicator of how much the disk “sticks out” or “sinks” inward relative to the center of the wheel.

The offset 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” inward).
• 🔹 Zero (ET0) - the plane coincides with the center of the rim.
• 🔹 Negative (ET-10, ET-20) - the plane is shifted to the inside (the disk “sticks out” outward).

For example, the inscription ET45 on the disk means that the mating plane is 45 mm inward from the center. The higher the number, the deeper the disk “sits” in the arch. This parameter directly affects wheelbase width, stress on wheel bearings and even tire wear.

Why do you need an ET departure: physics and safety

Many people think that relegation is simply a matter of “beautiful or ugly.” In fact, it performs three critical functions:

1. Load distribution. Proper ET ensures even pressure on the wheel bearing. If the overhang is too large or small, the bearing will wear out 2-3 times faster.
2. Maintaining suspension geometry. Changing the offset shifts roll-in shoulder (the point of contact of the wheel with the road), which leads to unpredictable behavior of the car when cornering.
3. Anti-crash protection. A disc with incorrect ET may snag on the brake caliper, shock absorber or inner part of the arch, especially when the car is fully loaded.

Manufacturers calculate the offset based on car weight, suspension type and wheel size. For example, at Volkswagen Golf VII standard ET for R16 wheels - ET51, and Toyota Land Cruiser 200 — ET25. The difference is due to different suspension design and weight distribution.

How offset affects handling: real consequences

Let's look at what happens if you install disks with non-standard ET. Let's look at situations using a sedan as an example. Skoda Octavia with factory offset ET45:

ET deviation	Consequences for handling	Risks for suspension
ET35 (less by 10 mm)	The steering becomes “sharp”, the car reacts faster to turns. Vibrations are possible at speeds over 100 km/h.	The load on the outer balls of the bearing increases. Risk of premature wear after 20–30 thousand km.
ET55 (more by 10 mm)	The steering wheel is “wobbly”, the car holds its trajectory worse. During a sharp maneuver, the front axle can be demolished.	The operation of the shock absorbers is disrupted, and the wear of the silent blocks of the levers is accelerated.
ET20 (less by 25 mm)	Strong “nervousness” of the steering wheel, the car “throws” along the ruts. On wet roads there is a high risk of hydroplaning.	Critical load on the hubs. The bearing may fail after 5–10 thousand km.

It is especially dangerous to change the reach on vehicles with independent multi-link suspension (for example, Audi A4 or BMW 3-series). Here, even a deviation of 5 mm can lead to uneven tire wear and loss of directional stability.

⚠️ Attention: On four-wheel drive vehicles (eg Subaru Forester or Mitsubishi Outlander) changing the offset on one axle can lead to differential failure due to the difference in wheel load.

How to measure disc offset yourself

If you are buying used wheels or are in doubt about the markings, the offset can be measured manually. You will need:

• 📏 Ruler or caliper (more precisely).
• 🪛 Square (or any object with a right angle).
• 📝 Calculator.

Procedure:

1. Place the disc on a flat surface face up.
2. Attach the square to the rim and measure the distance from the mating plane to the edge of the disc (parameter A).
3. Turn the disc over and measure the distance from the mating plane to the opposite edge (parameter B).
4. Calculate the offset using the formula:

   ET = (A + B)/2 – B

   For example, if A = 100 mm and B = 120 mm, then ET = (100 + 120)/2 – 120 = –10 mm.

An alternative method can be used to check:

Alternative way to measure ET

Remove the disc from the car, place it on the hub and measure the distance from the inner edge of the rim to the hub (parameter C). Then measure the width of the rim (parameter D). The offset is calculated as: ET = C – D/2.

Is it possible to install wheels with a different offset?

Theoretically, yes, but with reservations. Manufacturers allow minor deviations (usually ±5 mm), but only if:

• 🔧 The disc does not touch the suspension or body elements.
• 🚗 The car is not used in an aggressive style (drift, off-road).
• ⚖️ The total weight of the wheel (rim + tire) does not exceed the factory weight.

However, there are cases where a change in ET strictly prohibited:

⚠️ Attention: On vehicles with air suspension (for example, Mercedes-Benz S-Class or Audi A8) even the slightest deviation in offset can damage the adaptive damping system. Repairs will cost 100+ thousand rubles.

If you have to choose between wheels with ET35 and ET45 for a car with factory ET40, it is better to take ET45 — a slight “drowning” of the disk inward is less critical than its protrusion outward. But remember: even in this case, you will have to check more often wheel alignment and condition of bearings.

What to do if there are no suitable disks?

The situation is familiar to many: the store does not have the required ET, and there is no time to wait for delivery. In this case, there are three options to consider:

1. Use spacers. Aluminum or steel spacers compensate for the difference in offset. For example, if the factory is ET45, and the disk has ET35, you need a spacer 10 mm thick. But remember: spacers increase the load on the hub bolts and may require replacing them with longer ones.
2. Find discs with similar ET. A deviation of up to ±3 mm for passenger cars and up to ±5 mm for SUVs is permissible. The main thing is to check that there is no interference with the caliper.
3. Boring the disc hub. In some cases, it is possible to increase the overhang by grinding off the mating plane on a lathe. But this is risky: the structure of the disk is weakened, and it can crack upon impact.

The safest way is to order wheels with the required ET from an official dealer or a trusted manufacturer. For example, companies BBS, OZ Racing or Kosei Wheels are made to order with any offset.

If you do decide to use spacers, keep an eye on:

• 🔩 Material - only aluminum or alloy steel.
• 📏 Thickness - no more than 20 mm for passenger cars.
• 🔧 Fastening - bolts should be 5–10 mm longer than standard ones.

Myths and misconceptions about disc ejection

There are many myths surrounding the ET departure. Let's look at the most common ones:

Myth 1: “Offset is not important if the wheel width is the same”

🚫 Reality: Wheel width and offset are different parameters. For example, disk 8Jx18 ET35 may not fit on a car with factory 7.5Jx18 ET40, even if the width “fits” into the arch.

Myth 2: “Negative offset improves handling”

🚫 Reality: Yes, on sports cars negative ET increases the track width, but for civilian cars this is fraught with:

• 🔥 Increased wear of bearings.
• 🔥 Deterioration of directional stability at high speed.
• 🔥 Risk of wheels hitting when fully loaded.

Myth 3: “If the disc fits on the hub, then the offset is correct”

🚫 Reality: The disc may physically “sit” on the hub, but still have incorrect ET. The consequences will appear later: vibrations, uneven tire wear, play in bearings.

Myth 4: “Reach is not important on SUVs”

🚫 Reality: Just the opposite! U Toyota LC 200 or Nissan Patrol Reach is strictly regulated due to high loads on the suspension. For example, on LC 200 factory ET25, and a deviation of even 10 mm will lead to breakage of the ball joints.

FAQ: Frequently asked questions about ET disc ejection

Is it possible to install wheels with ET0 on a car with factory ET45?

No, this is a critical deviation. A difference of 45mm will move the wheel center outwards resulting in:

• 🔴 Heavy load on wheel bearings (risk of jamming).
• 🔴 The wheel touching the arch or caliper when turning.
• 🔴 Unpredictable behavior on a slippery road.

The exception is if you install spacers 45 mm and use extra long bolts.

How does offset affect tire wear?

Wrong ET changes wheel angle (collapse), which leads to:

• 🔹 One-sided wear (for example, “eats” the inside of the tread).
• 🔹 Undulating wear when the ET deviation is more than 10 mm.
• 🔹 Reduced tire life by 20–30%.

Example: on Honda CR-V with factory ET40, wheels with ET20 lead to wear of the inner part of the tire after 10 thousand km.

Is it possible to drive with different offsets on the front and rear axles?

Absolutely not! Different ET on axes leads to:

• 🚨 Uncontrolled skidding when braking.
• 🚨 Differential damage (on all-wheel drive vehicles).
• 🚨 Uneven braking, which increases the braking distance.

The exception is some sports cars (for example, BMW M3), where the rear wheels are purposely designed to have a longer offset to improve handling. But this is a factory setting, not a homemade modification.

Which offset is better for tuning: positive or negative?

It all depends on the goal:

• 🔧 Negative ET (for example, ET-10) visually widens the track, making the car “wider”. Suitable for show cars, but requires suspension modifications.
• 🔧 Positive ET (for example, ET50) “hides” the wheel in the arch, which is useful for rally cars (protection from dirt).

Optimal for civilian tuning neutral ET (close to factory) using spacers (thin spacers up to 10 mm).

Where can I see the factory offset for my car?

Look for information in the following sources:

• 📄 Instructions for use (section “Wheels and Tires”).
• 🖥️ Manufacturer's official website (for example, Toyota or Volkswagen).
• 🔧 Spare parts catalogs (for example, ETKA for VAG or EPC for Mercedes).
• 📱 Mobile applications like Wheel-Size or TireRack.

For example, for Kia Sportage 4th generation factory offset:

• 🔹 R17 — ET44
• 🔹 R18 — ET40
• 🔹 R19 — ET38