Parameter ET (or disc offset) is one of those technical characteristics that many car owners ignore when buying wheels, but in vain. An incorrectly selected offset can lead to accelerated bearing wear, unstable vehicle behavior on the road, or even conflict with the arches when cornering. And if an error with the diameter or width of the disk is immediately obvious, then the wrong ET will manifest itself only after thousands of kilometers - when it is already too late.

In this article, we will look at what is hidden behind these two letters, why manufacturers so strictly regulate the offset for each car model, and whether it is possible to deviate from the factory recommendations without consequences. You will also learn how to measure yourself ET, what to do if the required offset is not on sale, and why wheels with the “wrong” parameter are sometimes still installed (spoiler: it’s risky).

First, remember: ET (from German EinpressTiefe) is the distance from the mating plane of the disk (the one that is pressed against the hub) to the imaginary central axis of the disk. It is measured in millimeters and can be:

  • 🔹 Positive (for example, ET45) - the mating plane is shifted to the outer side of the disk.
  • 🔹 Zero (ET0) - the plane coincides with the central axis.
  • 🔹 Negative (ET-10) - the plane is shifted inward, towards the hub.

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1. Why ET disk flight is so important: physics and consequences of errors

Departure directly affects track width (the distance between the wheels of one axle) and the distribution of loads on the suspension. Even a deviation of ±5 mm from the manufacturer's recommended value may:

  • 🚗 Increase wear wheel bearings and silent blocks due to displacement of the force vector.
  • 🔧 Reduce steering accuracy — the car will “float” along the road.
  • 💥 Lead to harassment disc on the brake caliper or suspension elements when the steering wheel is fully turned.

Case study: on Volkswagen Golf IV factory offset of front discs - ET45. If you install disks with ET38 (difference in 7 mm), the wheel will move outward by 3.5 mm on each side. Seems like a small thing? But at the same time:

  • The load on the wheel bearing will increase by 15–20% (test data ADAC).
  • The suspension arms will operate at the wrong angle, accelerating bushing wear.
  • During a sharp maneuver, the wheel may hit the plastic fender liner.
⚠️ Attention: On rear wheel drive vehicles (eg BMW 5 Series E39) error in offset is more critical than on front-wheel drive. Here, wheel displacement affects the kinematics of the multi-link suspension, which can lead to irreversible damage to silent blocks already after 10–15 thousand km.

And now the main thing: Manufacturers calculate ET taking into account vehicle weight, suspension type and even axle load distribution. By changing the offset, you upset the balance laid down by the engineers at the design stage.

📊 Have you ever paid attention to the ET parameter when purchasing disks?
Yes, I always check
Sometimes, if I remember
No, I didn't know it was important
I buy CDs "like a friend"

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2. How to correctly measure the offset of an ET disc at home

If the offset is not indicated on the disk itself (and this happens with used or uncertified products), you can calculate it yourself. You will need:

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

Measurement algorithm:

  1. Place the disc on a flat surface face down.
  2. Place the square against the rim with one side resting on the mating plane (where the disc attaches to the hub).
  3. Measure the distance from the bottom edge of the square to inner edge of the rim (we denote it as X).
  4. Turn the disc over and measure the distance from the mating plane to outer edge of the rim (we denote it as Y).
  5. Calculate the offset using the formula: 
    ET = (X + Y)/2 – X

    For example, if X = 100 mm, and Y = 150 mm, then ET = (100 + 150)/2 – 100 = 25 mm.

Important: measurements are taken along the edge of the rim, and not along the edge of the rubber! Also keep in mind that on cast wheels the mating surface may be recessed - use a caliper for accuracy.

Make sure the rim is clean and not warped|Use an accurate tool (a caliper is better than a ruler)|Measure along the edge of the rim, not the tire|Repeat measurements 2-3 times for accuracy-->

⚠️ Attention: On discs with zero or negative offset (for example, ET0 or ET-15) the mating plane is shifted to the center or inward. In this case, the formula remains the same, but X there will be more Y, and the result is negative.

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Below is a table of factory offset parameters for common models. Please note: even within the same model, offset may vary depending on engine modifications or suspension type (for example, at Skoda Octavia A5 front-wheel drive and all-wheel drive versions have different ET).

Make and model Year of manufacture Factory ET (front/rear) Permissible deviation
Toyota Corolla (E170) 2013–2019 ET45 / ET45 ±3 mm
Volkswagen Passat B6 2005–2010 ET48 / ET40 ±2 mm (rear is stricter!)
Ford Focus III 2011–2018 ET50 / ET50 ±4 mm
Hyundai Solaris (RB) 2017–2023 ET46 / ET46 ±3 mm
BMW 3 Series (E90) 2005–2013 ET34 / ET37 ±1 mm (critical!)

Data is current for basic versions. In sports modifications (for example, Ford Focus ST or BMW M3) departure may vary! Always check with instruction manual or the disk manufacturer's database (for example, BBS, OZ Racing).

Why does BMW have such strict requirements for ET?

In BMW cars, the multi-link suspension is sensitive to changes in geometry. Even a deviation in 2–3 mm leads to uneven tire wear and increased load on the silent blocks. In addition, the rear axle uses plain bearings, which do not tolerate distortions.

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4. Is it possible to install wheels with a different offset? Risks and exceptions

Theoretically, yes, but with reservations. Here's when it's acceptable:

  • 🔧 Deviation within ±5 mm for most front-wheel drive cars (for example, Kia Rio, Renault Logan). But even here it is better to stick ±3 mm.
  • 🚘 Installing spacers (if ET is too large, i.e. the wheel is “recessed”). Spacers compensate for the difference, but require extended bolts and increase the load on the hub.
  • 🏁 Tuning projects, where the change in offset is part of a planned suspension modification (for example, widening the track for drifting). In this case required replacement of levers, shock absorbers and wheel alignment adjustments.

And now about when it's impossible experiment:

  • 🚫 On cars with multi-link suspension (for example, Audi A4 B8, Mercedes C-Class W204). Here the offset is strictly tied to the kinematics.
  • 🚫 If the difference exceeds ±10 mm - this is guaranteed to lead to accelerated wear bearings and tires.
  • 🚫 On all-wheel drive vehicles (for example, Subaru Forester, Mitsubishi Outlander), where the change in offset upsets the balance of the center differential.

Case Study: Owner Nissan Qashqai J10 installed disks with ET35 instead of the factory one ET40. After 8 thousand km, play appeared in the front right bearing, and during diagnostics it turned out that the silent blocks of the levers were “broken” due to an incorrect load vector.

💡

If you like non-standard ET drives but are unsure about compatibility, use 3D modeling. Services like Wheel-Size.com allow you to virtually “try on” the wheels on your car model and see possible conflicts with the arches or calipers.

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5. Disc spacers: salvation or crutch?

Spacers (or spacers) are metal rings that are installed between the disc and the hub to reduce effective overhang. They are:

  • 🔹 Universal (suitable for most cars, but require checking the bore diameter).
  • 🔹 Model (developed for a specific brand, for example, for Volkswagen or Toyota).
  • 🔹 With centering ring (for discs with a large central hole).

Pros of spacers:

  • ✅ Allows you to install wheels with the “wrong” ET without replacing the suspension.
  • ✅ Cheaper than buying new discs.
  • ✅ You can choose the thickness in increments 1 mm for a precise fit.

Disadvantages and risks:

  • ❌ Increase the load on the wheel bearings (especially if the spacer thickness is > 15 mm).
  • ❌ Required extended bolts or studs, which weakens the fastening.
  • ❌ May cause vibration at high speeds if unbalanced.

Example of correct usage: on Lada Vesta factory offset - ET40. If you want to install disks with ET30, sufficiently thick spacers 10 mm. But be sure to:

  1. Buy bolts at 10mm longer standard
  2. Check whether the wheel touches the caliper when the steering wheel is turned completely.
  3. Do wheel alignment after installation.
⚠️ Attention: Spacers thicker than 20 mm are considered unsafe for everyday use. They significantly change the suspension geometry and can lead to loss of control at high speeds.

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6. How to choose wheels according to ET: step-by-step instructions

To avoid mistakes with a crash, follow this algorithm:

  1. Find out factory ET for your model. Sources:
    • 📄 Operating manual (section "Wheels and tires").
    • 🖥️ Official website of the manufacturer (for example, Toyota TechDoc).
    • 🔍 Disk databases (for example, Alloy Wheels Direct or TireRack).
  • Check compatibility according to the disc manufacturer's tables. For example, on the site BBS There is a filter by car brand.
  • Compare with existing drives (if they are original). ET is usually listed on the inside in the format ETXX.
  • Consider the width of the rim. The wider the disk, the the offset should be less (otherwise the wheel will stick out). Formula: 
    Tolerance ET = (Width of new rim - Width of original rim) / 2

    For example, if a standard disk 7J, and the new one 8J, the offset can be reduced by 5 mm.

  • Consult with a specialist on the suspension if you plan to deviate from the factory parameters.

    • Example: you want to bet on Skoda Octavia A7 rims wide 8J instead of regular ones 7J. Factory offset - ET45. According to the formula:

    (8 – 7) / 2 = 0,5 → you can take disks from ET40 (but no less!).

    💡

    Even if the discs physically fit onto the hub, this does not guarantee their compatibility. Always check ET, center bore diameter (DIA) and bolt pattern (PCD) together!

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    7. Frequent mistakes when choosing wheels by offset

    Experienced tire fitting experts identify several typical mistakes:

    • 🔴 Ignoring ET difference for front and rear axle. For example, on Ford Mondeo IV front ET50, and behind - ET45. Installing identical disks will lead to imbalance.
    • 🔴 Buying disks "by appearance". Discs from Audi A4 can physically approach Volkswagen Passat (same bolt pattern), but their offset is different!
    • 🔴 Disk width not taken into account. A narrow disk with a large ET can “drown” the wheel inside the arch, and a wide one with a small ET can push it beyond the dimensions of the car.
    • 🔴 Using spacers without extended bolts. This leads to under-reaped disk and vibrations.

    Real life example: owner Kia Sportage 3 bought wheels from Hyundai Tucson (same bolt pattern 5×139.7). However, the departure Tucson — ET40, and Sportage — ET46. As a result, when turning, the wheel touched the plastic fender liner, and after 20 thousand km play appeared in the steering rack.

    To avoid such mistakes, always check the parameters against VIN code car or use specialized catalogs (for example, Alloy Wheel Fitment Guide).

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    FAQ: Answers to frequently asked questions about ET disk failure

    ❓ Is it possible to install disks with ET smaller than the factory one? For example, instead of ET45 take ET38?

    Technically you can, but the wheel will move outward, which will increase the load on the bearings and suspension arms. Permissible deviation - up to –5 mm from factory ET (for most cars). For example, if the normal departure ET45, minimum acceptable - ET40. But it’s better not to take risks and use spacers.

    ❓ What happens if you install wheels with ET larger than the factory ones?

    The wheel will “sink” inside the arch. Consequences:

    • Contact with brake calipers or suspension components.
    • Reduced track width, which reduces cornering stability.
    • Risk of damage to the inside of the tire from the wheel arch liner.

    If the difference is up to +5 mm, can be compensated spacers (but this will reduce ground clearance).

    ❓ What is the ET of SUV rims?

    Most SUVs (eg. Toyota Land Cruiser 200, Nissan Patrol) departure negative or zero: from ET0 up to ET–25. This is due to:

    • Wider wheels (you need to “pull” them outwards).
    • Strengthening the suspension (it is less sensitive to changes in loads).
    • The need to increase ground clearance.

    But even here it is not recommended to deviate from the factory parameters by more than ±10 mm.

    ❓ Does ET affect tire wear?

    Yes, and very significant. Incorrect departure leads to:

    • Uneven tread wear (for example, sawtooth wear at the edges).
    • Increased load on the inner or outer part of the tire.
    • Reducing tire service life by 20–30%.

    Example: on Honda CR-V with disks ET30 instead of ET40 the tires wore out along the outer edge after 15 thousand km.

    ❓Where can I check disk compatibility for ET online?

    Use these resources:

    Enter the make, model and year of manufacture of the car - the system will show the acceptable parameters.