Disc offset ET40 and ET50: what is the difference and how does it affect the car?

Selecting wheels is a task that requires attention to detail. One of the key parameters that beginners often forget about is disc offset (denoted as ET). Numbers ET40 and ET50 may seem like a minor difference, but in practice they determine how the disc will “sit” on the hub, affect the suspension load and even the handling of the car.

Many car owners mistakenly believe that a difference of 10 mm is insignificant. However, even such a seemingly small shift can lead to accelerated bearing wear, a change in track width and, in the worst case, a conflict between the disc and the elements of the brake system or the arch. In this article, we will look at what these numbers mean, how they affect the behavior of the car, and what consequences await those who ignore the manufacturer’s recommendations.

In order not to get confused in terms, let's start with the basics: disk ejection (ET, from German EinpressTiefe) is the distance between the mating plane of the disk (the one that is pressed against the hub) and the imaginary central axis of the disk. Measured in millimeters. If ET positive (for example, ET40), the disk is “recessed” inward relative to the axis. Negative offset (for example, ET-20) means that the disc is protruding outwards. Zero (ET0) - the axis and the mating plane coincide.

Now to the point: why the difference between ET40 and ET50 important? At first glance, 10 mm is not much, but in the context of suspension geometry it can mean shifting the center of gravity of the wheel closer to the body or, conversely, outward. The consequences depend on the design of the car, the width of the rim and even the driving style. Next, we will analyze each aspect in detail - from theory to practical advice on selection.

What is disc offset and how is it measured?

Disc offset is not just a number on the marking, but critical geometric parameter, which affects the distribution of loads in the suspension. To understand how ET40 different from ET50, you need to understand the principle of measurement.

Imagine a disc in cross-section: its central axis runs exactly in the middle of the rim. The mating plane is the surface of the disc that is pressed against the hub by the bolts. Departure (ET) is the distance from this plane to the central axis. If the axis and plane coincide, the offset is zero (ET0). If the plane is shifted to the center of the car, the offset is positive (ET40, ET50), if outward - negative (ET-10, ET-20).

The formula for calculating the departure is simple:

ET = X - Y/2

where:

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

For example, if X = 120 mm, a Y = 200 mm (disc width 8 inches), then ET = 120 - (200/2) = 20 mm (ET20). Manufacturers indicate offset to the nearest millimeter, and a deviation of even 5 mm can be critical for some car models.

ET40 vs ET50: what changes with a difference of 10 mm

Difference between ET40 and ET50 - this is displacement of the mating plane by 10 mm closer to the center of the car. In practice, this means that a disk with ET50 will be “recessed” deeper under the arch, and with ET40 - stick out a little. What consequences does this have?

Firstly, it changes track width (distance between the centers of wheels on the same axle). When ET50 the wheels are closer to each other, which can:

• ⚠️ Increase the load on the wheel bearings (due to a displacement of the force vector).
• 🔄 Change the contact patch of the tire with the road (especially on wide rims).
• 🚗 Affect directional stability at high speeds.

Secondly, it shifts wheel center of gravity. Disc with ET40 will carry the mass out a little, which can:

• ➕ Improve grip in corners (due to a wider track).
• ➖ Increase the load on the suspension arms and ball joints.
• 🔧 Require wheel alignment adjustment (if the offset is very different from the standard one).

It is important to understand that there is no universal “best” offset. For light city cars (Volkswagen Polo, Hyundai Solaris) ET50 may be optimal, and for heavy SUVs (Toyota Land Cruiser) — ET40 or even ET20. It all depends on the suspension design and mass distribution.

Consequences of incorrect departure: from wear to accidents

Ignoring the recommended departure is not just a risk of losing the warranty, but direct security threat. This is what can happen if you install a disk with the wrong ET:

1. Accelerated suspension wear:

- Shifting the center of gravity of the wheel increases the load on step bearings, ball joints and levers. For example, on Ford Focus with staff ET50 installation ET40 can reduce bearing life by 30–40%.

- On vehicles with multi-link suspension (e.g. Audi A4, BMW 3-series) incorrect offset leads to uneven wear of silent blocks and bushings.

2. Deterioration in handling:

- Disc with ET40 instead of ET50 will make the steering wheel “heavier” and less responsive (due to the increased rolling shoulder).

- On the contrary, ET50 instead of ET40 may cause "yaw" in a straight line at high speeds (especially noticeable at Toyota Camry or Skoda Octavia).

3. Conflict with the brake system or arch:

- Disc with less ET (for example, ET40 instead of ET50) may hurt caliper or boot when the car is fully loaded.

- On the contrary, ET50 instead of ET40 sometimes leads to the fact that the wheel “rests” against the inside of the arch when the steering wheel is turned at maximum (relevant for Renault Duster or Nissan Qashqai).

4. Wheel alignment problems:

- Even if the disc physically fits onto the hub, the changed offset shifts the suspension geometry. This may make it impossible to adjust the camber correctly, resulting in uneven tire wear.

⚠️ Attention: On vehicles with all-wheel drive (Subaru Forester, Mitsubishi Outlander) incorrect offset can cause increased load on the transmission due to changes in the operating angles of the CV joints. This is fraught with their accelerated failure.

How to determine the permissible offset for your car

The manufacturer always indicates the recommended disc offset in instruction manual or on a sticker in the doorway (next to the tire pressure information). If documentation is lost, use the following methods:

1. Official sources:

- Go to the car manufacturer’s website (section “Technical Specifications” or “Accessories”).

- Check the spare parts catalogs (ETKA for VW/Audi, EPC for Mercedes).

- Examples of regular flights:

• 🚗 Lada Vesta: ET35-45 (depending on the engine and year).
• 🚗 Kia Rio 4: ET46-52.
• 🚗 BMW X5 (G05): ET20-35 (depending on the width of the disk).

2. Practical measurement:

If you already drive non-standard wheels and don’t know their offset, you can approximately calculate it:

Remove the rim from the vehicle and clean the mating surface|Measure the width of the rim (Y) in millimeters|Measure the distance from the mating surface to the inner edge (X)|Apply the formula ET = X - Y/2-->

3. Online services:

- Sites like WillTheyFit.com or TireSize.com allow you to check disk compatibility based on parameters, including ET.

- Enter the car model, and the system will show the permissible offset ranges.

⚠️ Attention: If you buy discs secondhand or at a dealership, be sure to check the offset with a caliper. There are often cases when sellers confuse ET40 and ET50 or provide incorrect information.

Is it possible to install wheels with an offset of ET40 instead of ET50 and vice versa?

This is one of the most frequently asked questions, and the answer is not clear-cut. It all depends on suspension designs, rim width and driving style. Let's look at typical scenarios:

1. ET40 instead of ET50 (offset 10 mm less):

- Pros:

- The wheel protrudes slightly outward, which can improve directional stability (due to the wide track).

- On some cars (for example, VAZ 2110) this allows you to install wider wheels without touching the arch.

- Cons:

- The load on wheel bearings and levers increases.

- Possible problems with wheel alignment (especially on cars with multi-link suspension).

- Risk of the caliper touching when the car is fully loaded.

2. ET50 instead of ET40 (offset by 10 mm more):

- Pros:

- The wheel is “recessed” under the arch, which reduces the risk of damage to the disk when parking near curbs.

- Less load on bearings (but this is only relevant for light cars).

- Cons:

- Reducing the track width may reduce cornering stability.

- On some models (for example, Toyota RAV4) disk with ET50 instead of ET40 touches the inside of the arch when the steering wheel is turned to maximum.

When can you experiment?

- If the difference in offset does not exceed ±5 mm from the staff (for example, ET45 instead of ET50).

- If the car is light (for example, Daewoo Matiz or Hyundai i10), and the suspension is not sensitive to changes in geometry.

- If you are ready to check the condition of bearings and silent blocks every 10–15 thousand km.

When is it absolutely forbidden?

- On vehicles with independent multi-link suspension (Audi A6, Volvo S60).

- On cars with all-wheel drive (due to the risk of damage to CV joints).

- If the difference in offset exceeds 10 mm (for example, ET30 instead of ET50).

Car model	Regular departure	Permissible deviation	Risks when exceeded
Lada Granta	ET35-40	±5 mm	Bearing wear, arch contact
Toyota Corolla (E210)	ET45	±3 mm	Deterioration in controllability, vibration
BMW 3-series (G20)	ET30-35	±2 mm	Damage to CV joints, incorrect camber
Nissan X-Trail (T32)	ET40	±5 mm	Conflict with brake caliper

How to choose wheels with abnormal offset: expert advice

If you still decide to deviate from the manufacturer's recommendations (for example, for tuning or installing wide rims), follow these rules to minimize risks:

1. Use spacers (adapters):

- Spacers allow you to compensate for differences in offset. For example, if you need ET40, and the disk has ET50, spacer thickness 10 mm will solve the problem.

- Important: spacers must be certified and are made of aluminum alloy (not steel to avoid imbalance).

2. Check compatibility with the brake system:

- On vehicles with large brake discs (Audi RS, BMW M) even a slight offset in offset can lead to a conflict with the caliper.

- Before purchasing discs with non-standard ET remove the wheel and check the clearances.

3. Consider the width of the rim:

- The wider the disk, the more critical the overhang. For example, on disk 8J difference in ET 10 mm will have a stronger effect than 6J.

- For wide rims (9J and more) it is better not to deviate from the standard departure by more than ±3 mm.

4. Do a wheel alignment after installation:

- Even if visually “everything is in order”, the changed offset may require adjustment of the wheel alignment angles.

- Some service stations have special equipment for checking suspension geometry after installing non-standard disks.

5. Monitor the condition of the suspension:

- After installing disks with non-standard ET every 5–7 thousand km check:

• 🔧 Backlash in wheel bearings.
• 🔧 Condition of silent blocks and ball joints.
• 🔧 Uniform tire wear.

What happens if you ignore the recommendations?

In practice, there are cases when installing discs with an offset ET30 instead of the regular one ET50 on Honda CR-V led to the destruction of the wheel bearing after 20 thousand km. Restoring the suspension in such cases costs 3-5 times more than saving on the “wrong” disks.

Myths and misconceptions about disc wear

There are many myths surrounding the topic of discs coming off, which can mislead even experienced car owners. Let's look at the most common ones:

1. “If the disc fits on the hub, it means it fits”

- ❌ Reality: Physical compatibility of fasteners (PCD, center hole diameter) does not guarantee correct geometry. The offset affects the distribution of loads that are not visible to the eye.

2. “A difference of 10 mm is insignificant”

- ❌ Reality: On light cars (Hyundai Getz) this may not be critical, but on heavy (Mercedes GL) such a difference leads to accelerated wear of the suspension.

3. “You can compensate for the offset with spacers of any thickness”

- ❌ Reality: Spacers are thicker 15–20 mm require extended bolts or studs, which weakens the disk fastening. In addition, they increase the load on the hub.

4. "Negative departure (ET-20) is always better for appearance"

- ❌ Reality: Discs with a negative offset shift the center of gravity outward, which increases the load on the bearings and arms. This is true for tuned cars, but requires reinforced suspension.

5. “If the disks are on the same model, then they will fit”

- ❌ Reality: The same car may have different offset recommendations depending on the year of manufacture, engine or configuration. For example, Volkswagen Golf IV has in the database ET38, and in the version GTI — ET35.

6. “The departure does not affect fuel consumption”

- ❌ Reality: Changed suspension geometry can increase rolling resistance and worsen aerodynamics, which will lead to increased fuel consumption. 0.3–0.7 l/100 km.

FAQ: Answers to frequently asked questions about ET40 and ET50 departures

Is it possible to install wheels with ET40 on a car with standard ET50 if you use spacers?

Yes, but with reservations:

• The spacer must be thick 10 mm (difference between ET50 and ET40).
• The material of the spacer is aluminum alloy (not steel or plastic).
• Be sure to check that the spacer will not conflict with the brake caliper.
• After installation, do a wheel alignment.

⚠️ On vehicles with all-wheel drive (Subaru Impreza, Mitsubishi Lancer) even with spacers, the risk of damage to CV joints remains.

How does offset affect tire wear?

Incorrect offset changes the wheel alignment angles, which leads to:

• 🔥 Shoulder wear (if the offset is less than standard).
• 🔥 Spotted wear (if the overhang is greater than standard).
• 🔥 Accelerated grinding of the inner or outer edge (depending on the offset).

For example, on Skoda Octavia with staff ET45 installation ET35 leads to wear of the inner part of the tire after 10–15 thousand km.

Why do different sources indicate different offsets for the same car?

This is due to:

• 📄 Different configurations (for example, Toyota Camry has in the database ET45, and in the version TRD — ET40).
• 📄 Year of issue (restyled models may have a different offset).
• 📄 Sales market (export versions sometimes use discs with different ET to adapt to local roads).

Always be data-driven VIN decoder or an official dealer.

Can an incorrect flight cause a warranty repair to be denied?

Yes. If, when diagnosing a suspension malfunction (for example, failure of a wheel bearing), the technician discovers that discs with an abnormal offset are installed, warranty repairs will be performed. they will refuse. This is stated in the warranty conditions of most manufacturers (Hyundai, Kia, Volkswagen).

An exception is if the departure differs by no more than ±3 mm (for some models the tolerance is greater).

Which offset is better for tuning: ET40 or ET50?

It depends on the purpose:

• 🚗 For visual tuning (wide rims, aggressive look) are more often chosen ET40 or even ET20, but this requires modification of the suspension.
• 🏁 For sporty driving (track, drift) preferable ET50, as it reduces the load on the bearings under high lateral forces.
• 🛣️ For daily use It’s better to stick to the standard offset or deviate no more than ±5 mm.

Remember: tuning wheels often require reinforced wheel bearings and adjustable levers to correct the camber.