Offset on car rims (ET): what it is, how to measure it and what it affects

Have you ever wondered why some wheels fit your car perfectly, while others - even if the diameter and width are the same - look “wrong”? Or why, after replacing the wheels, the car began to handle worse, and the tires “eat away” from the inside? The reason often lies in one small but critical parameter - disc ejection (ET).

Overhang (or offset) is the distance from the mating plane of the disk (the one that is pressed against the hub) to its central axis. It is measured in millimeters and can be positive, zero or negative. Even a millimeter deviation from the manufacturer’s recommended value can change the load on the suspension, worsen directional stability and shorten tire life. In this article we will look at what it is ET on rims, how to measure it correctly, what types of offset there are, and why you can’t ignore this parameter when choosing wheels.

What is disc ejection (ET) and why is it needed?

Disc offset (indicated as ET from German EinpressTiefe - “pressing depth”) is a geometric parameter that determines the position of the wheel relative to the hub. It affects:

• 🔧 Load on wheel bearings - incorrect offset shifts the center of gravity of the wheel, accelerating wear.
• 🚗 Vehicle handling — changes the rolling shoulder, which can make the steering wheel “tight” or, conversely, too light.
• 🔄 Suspension performance — shifting the wheels outward or inward increases the load on the levers and shock absorbers.
• 🛞 Tire wear - incorrect ET leads to uneven wear of the tread.

The car manufacturer calculates the optimal offset taking into account the weight of the car, the type of suspension and load distribution. For example, for Volkswagen Golf VII standard ET front wheels - ET45, and for Toyota Land Cruiser 200 — ET25. Deviation from these values ​​is fraught with consequences, which we will discuss further.

It is important to understand that relegation is not just a “beautiful” position of the wheel in the arch. This is an engineering parameter that affects safety. For example, decreasing ET (when the disc “sticks out”) increases the load on the external bearings and can lead to their overheating, and an increase (when the disc is “recessed” inward) can lead to contact with a suspension part when the steering wheel is turned completely.

Departure types: positive, zero and negative

There are three types of offset, and each affects the behavior of the car in its own way. Let's look at them with examples.

Departure type	Designation	Description	Application example
Positive	ET30, ET45	The mating plane is shifted inside relative to the center of the disk. The wheel is “recessed” under the arch.	Most sedans and hatchbacks (Skoda Octavia, Hyundai Solaris).
Zero	ET0	The mating plane coincides with the central axis of the disk.	Sports cars, tuned cars.
Negative	ET-15, ET-35	The mating plane is shifted outward. The wheel protrudes beyond the arch.	SUVs (Jeep Wrangler), wide rims for drifting.

In practice positive offset is most common - it is typical for civilian cars, as it allows you to “hide” the wheel under the arch, reducing air resistance and protecting the disc from damage. Negative departure used to visually widen the track (the car looks “wider”) or to install wider tires, but this is always a compromise: the load on the wheel bearings and steering increases.

Zero departure - rare in production cars, but popular in motorsport, where uniform distribution of loads is important. For example, on Porsche 911 GT3 often install disks with ET0 to improve handling on the track.

⚠️ Attention: Installing rims with negative offset on a vehicle not designed for this purpose may result in premature failure of wheel bearings (2–3 times faster) and an increased risk of the wheel “pulling out” during a sharp maneuver.

How to measure disc offset yourself

If you are buying used wheels or want to check compliance ET stated, you can measure the offset yourself. For this 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 (the one that presses against the hub).
2. Attach the square to the rim and measure the distance from the mating plane to the edge of the disc (A).
3. Turn the disc over and measure the distance from the mating plane to the opposite edge (B).
4. Calculate the offset using the formula: ET = (A + B)/2 – B.

Example: if A = 120 mm, and B = 100 mm, then ET = (120 + 100)/2 – 100 = 10 mm. This means that the offset is positive and equal to ET10.

If the disc is already installed on the car, you can measure the offset using laser level or rulers with a plumb line:

1. Raise the car on a jack or lift.
2. Place a ruler vertically on the center of the wheel (through the hub).
3. Measure the distance from the ruler to the inner and outer edges of the disc.
4. The difference between these distances, divided by 2, will give the actual offset.

⚠️ Attention: Even if the disk visually “stands” on the hub, this does not guarantee correct ET. For example, on BMW E39 you can physically install disks with ET30 instead of regular ones ET35, but this will lead to an increase in the load on the bearings by 15–20%.

Consequences of incorrect departure: from tire wear to an accident

Many car owners mistakenly believe that offset is a “trifle” that can be ignored if the disc physically sits on the hub. In practice, even a deviation in 5–10 mm can lead to serious problems:

• 🔥 Overheating and destruction of wheel bearings — a shift in the center of gravity of the wheel increases the load on the bearing, especially when driving at high speed.
• 🚘 Deterioration in handling — the car becomes “nervous” on the straight line and holds its trajectory worse in turns.
• 🛞 Uneven tire wear — the rubber is “eaten” on one side, which reduces its service life by 30–50%.
• 💥 Suspension damage — levers, shock absorbers and silent blocks operate at unpredictable angles, which accelerates their wear.
• ⚠️ The wheel alignment “goes away” after replacing the wheels - even if the angles were adjusted perfectly before.

Company Research Hunter Engineering (manufacturer of wheel alignment stands) showed that a change in offset by 10 mm increases the load on the hub bearing by 25–30%, and the risk of its premature failure by 1.5 times.

Case Study: Owner Kia Sportage installed disks with ET30 instead of regular ones ET42. After 10,000 km, a hum appeared in the front wheels, and during diagnostics it turned out that the bearings were “broken” and required replacement. The cost of repairs is about 15,000 rubles, while correct discs would cost 2,000 rubles more.

Is it possible to install wheels with a different offset?

Theoretically, yes, but with reservations. Manufacturers allow minor deviations from staff ET, but they should be:

• ✅ Within ±5mm for most passenger cars.
• ✅ Confirmed by calculations (for example, through specialized departure calculators).
• ✅ Taken into account in suspension settings (wheel alignment may need to be adjusted).

However, there are cases when even a minimal deviation is unacceptable:

• 🚗 Cars with multi-link suspension (Audi A4, Mercedes C-Class) - sensitive to changes in the rolling shoulder.
• 🏎️ Sports cars (BMW M3, Nissan GT-R) - designed for precise loads.
• 🚙 SUVs with permanent all-wheel drive (Toyota Land Cruiser, Mitsubishi Pajero) - changing the offset affects the operation of the differentials.

If you still decide to install disks with a different ET, required:

1. Consult a suspension specialist.
2. Check whether the disc touches the suspension elements when the steering wheel is turned completely.
3. Do a wheel alignment after installation.
4. Monitor the temperature of the hubs after a trip (overheating is a sign of increased load).

What is rolling leverage and why is it important?

The rolling shoulder is the distance between the point of contact of the tire with the road and the steering axis of the wheel. Changing the offset moves this point, which affects:

- steering stability (the car can “scour” along the road);

- feedback on the steering wheel (it becomes too light or heavy);

- tire wear (uneven load distribution).

For example, on Volvo S60 An increase in the rolling shoulder by 10 mm leads to an increase in steering effort by 15–20%.

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

To avoid problems, follow this algorithm when selecting disks:

1. Find out the standard offset for your model. It can be found:
   • In the vehicle owner's manual.
   • On a sticker in the doorway (usually indicated along with the tire sizes).
   • On the disk manufacturer's website (for example, Replica or K&K have compatibility bases).

Check tolerances. For most cars this is ±5 mm, but for some (for example, Porsche or Ferrari) - only ±2 mm.

Use the departure calculator. Online services (for example, WillTheyFit) will help calculate how the change ET will affect the position of the wheel.

Consider the width of the rim. The wider the rim, the more critical the overhang. For example, on disk 8J deviation in 5 mm will have a stronger impact than 6J.

Check bus compatibility. Some wheel and tire combinations may hit the arch even when properly ET.

Example: for Ford Focus III standard front wheel offset - ET50. If you want to install disks ET45, check:

• Does the wheel extend beyond the arch (visually and when the steering wheel is turned completely).
• Will the ground clearance decrease (important for low-slung cars).
• Will the suspension need to be modified (for example, installing spacers).

Spacers for adjusting offset: panacea or crutch?

Spacers (or adapters) are metal rings that fit between the hub and the disc to change the effective offset. They are:

• 🔄 Universal - Suitable for most cars, but require precise fitting.
• 🔧 Model — designed for a specific machine (for example, for Subaru Impreza or Mitsubishi Lancer).
• 🛠️ Homemade — are highly not recommended due to the risk of wheel imbalance.

Spacers can be useful in the following cases:

• 🚗 You bought discs with the wrong ET, but they fit perfectly in design.
• 🏁 You need to temporarily increase the track (for example, for drifting or rallying).
• 🔄 You want to “pull” the wheels out to improve the appearance (but be aware of the consequences!).

However, spacers have serious disadvantages:

• ⚠️ Increases the load on wheel bearings — even high-quality spacers shift the center of gravity.
• ⚠️ May cause vibrations - if the spacer is unbalanced or does not fit well.
• ⚠️ Requires extended bolts — regular ones may not reach the disk, which is dangerous.
• ⚠️ Illegal in some countries — in Russia their use is not prohibited, but in the event of an accident this can be regarded as a design change.

If you still decide to use spacers, follow the rules:

1. Choose spacers from aviation aluminum or steel (not from “raw” metal).
2. The thickness of the spacer should not exceed 15–20 mm (otherwise the risk of suspension failure increases exponentially).
3. Be sure to use extended bolts with the correct tightening torque.
4. After installation, do wheel balancing and check wheel alignment.

Example: on Nissan Qashqai spacers are often installed thick 10–15 mm for installing disks with ET35 instead of regular ones ET40. This gives a more aggressive look, but requires monitoring the condition of the bearings every 10,000 km.

FAQ: Frequently asked questions about disc wear

Is it possible to install wheels with an offset of ET35 instead of ET40?

Theoretically yes, but you need to consider:

• The wheel will move outward by 5 mm, which can lead to hitting the arch when the steering wheel is turned completely.
• The load on the wheel bearing will increase (by ~10–15%).
• Wheel alignment may need to be adjusted.

For most passenger cars, such a deviation is acceptable, but for cars with sensitive suspension (for example, BMW 5 Series) it is better to avoid changes.

What is the best offset for a lowered car?

When lowered, the vehicle's center of gravity is lowered, therefore:

• It is advisable to use discs with standard or slightly increased reach (for example, ET45 instead of ET40) to “sink” the wheel under the arch.
• Negative departure (ET-10) looks visually beautiful on lowered cars, but increases the risk of damage to the rims on the road.
• Be sure to check whether the wheel touches the suspension elements when the shock absorbers are fully compressed.

Does offset affect fuel consumption?

Yes, but indirectly. Incorrect departure:

• Increases rolling resistance (if the wheel is shifted outward).
• Can change roll-in shoulder, which affects handling and, as a result, driving style (frequent steering increases consumption).
• Leads to uneven tire wear, which also affects efficiency.

According to ADAC (German Automobile Club), departure deviation by 15 mm may increase fuel consumption by 1–3% due to modified aerodynamics and increased resistance.

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

No, this is extremely dangerous. Different offsets on the axles lead to:

• Unpredictable handling - the car can “steer” to the side.
• Uneven tire wear - one axis will “drag” the other.
• Increased load on the transmission (especially relevant for all-wheel drive vehicles).

The exception is some sports cars (for example, Nissan GT-R), where the offset of the front and rear wheels differs according to factory design, but this was calculated by the engineers.

What is the offset of wheels for SUVs?

The following values are typical for SUVs:

• Toyota Land Cruiser 200: ET25 (before) / ET25 (back).
• Nissan Patrol: ET10 or ET0 (depending on modification).
• Jeep Wrangler: ET-12 (for wide wheels).
• UAZ Patriot: ET30.

The negative offset here is due to the need to increase the track for better off-road stability. However, for city use such discs are not always justified due to increased wear on the suspension.