Have you ever noticed the inscription ET45 or ET30 on the inside of a car rim? These two letters and numbers are one of the most important parameters when choosing wheels, which directly affects handling, suspension wear and even driving safety. Many car owners mistakenly believe that the main thing is the diameter and bolt pattern, and the offset (ET) can be ignored. But such neglect often leads to serious problems: from premature wear of wheel bearings to loss of control over the car at high speed.
In this article we will look at what it is ET on disc, how to correctly decipher this parameter, why manufacturers so strictly regulate its values for each car model, and what will happen if you install wheels with the wrong offset. You will also learn how to measure the offset yourself if the markings have worn off, and what permissible deviations exist for tuning. The material will be useful for both beginners and experienced car enthusiasts who want to avoid costly mistakes when selecting wheels.
What is ET on disks: simple decryption
ET (from German EinpressTiefe) is an abbreviation for disc overhang, which refers to the distance between mating plane (the place where the disc is attached to the hub) and imaginary central plane of the rim. The offset is measured in millimeters and can be:
- 🔹 Positive (for example, ET40) - when the mating plane protrudes outward relative to the center of the disk.
- 🔹 Zero (ET0) - the mating plane coincides with the central axis.
- 🔹 Negative (for example, ET-15) - the mounting plane is recessed inward relative to the center.
Simply put, ET shows how much the disc “bulges” outward or “sinks” inward relative to the hub. This parameter directly affects wheelbase width, the load on the suspension and even the speedometer readings. For example, if you install disks with ET20 instead of recommended ET45, the wheels will move outward by 25 mm on each side, which will increase the load on the wheel bearings and can lead to hitting the arches when turning.
It is important to understand that relegation is not the width of the rim (it is denoted as J, for example, 7.5J) and not diameter (R17). This is an independent geometric parameter that the manufacturer calculates taking into account the weight of the car, the type of suspension and load distribution. Ignoring him is like putting wheels on Volkswagen Golf on Toyota Land Cruiser: Outwardly it may be suitable, but the consequences will be disastrous.
How does ET offset affect a car: 5 key consequences
Many car owners believe that a slight deviation in offset from factory recommendations is not critical. However, even the difference in 5–10 mm can lead to serious problems. Let's see how ET affects various aspects of vehicle operation.
| Reach change | Consequences for the car | Risks |
|---|---|---|
| ET less than recommended (for example, ET30 instead of ET45) | Wheels move outward, wider track | ⚠️ Accelerated wear of wheel bearings ⚠️ Touching the arches when turning ⚠️ Increased load on suspension arms |
| ET more than recommended (for example, ET50 instead of ET35) | The wheels “sink” inward, there is already a track | ⚠️Deterioration of controllability at high speed ⚠️ Risk of contact with brake calipers ⚠️ Uneven tire wear |
| Zero offset (ET0) on a vehicle with a positive factory ET | Wheels are pushed outward as far as possible | ⚠️ Increased load on the steering rack ⚠️ Risk of wheel tearing off due to a strong impact |
Incorrect offset is especially critical for vehicles with independent multi-link suspension (for example, Audi A4, BMW 3 Series). Here, even a minimal shift in the center of gravity of the wheels leads to uneven wear of silent blocks and deterioration of directional stability. And on all-wheel drive vehicles (for example, Subaru Forester or Mitsubishi Outlander) incorrect ET may cause increased vibration on the steering wheel due to an imbalance in the transmission.
⚠️ Attention: On some vehicles (for example, Mercedes-Benz or Porsche) disc offset is strictly tied to operation exchange rate stabilization systems (ESP). Installing disks with incorrect ET can lead to false alarms or even failure of the electronics.
How to determine the correct ET for your car: 3 reliable ways
To avoid problems associated with incorrect departure, you need to know exactly which ET valid for your car model. Here are three proven ways to get this information:
- Factory markings on disks or in documentation.
On original discs, the offset is indicated in the format ETXX (for example, ET42). You can also find the parameter:
- 📄 B instruction manual car (section “Wheels and Tires”).
- 🚗 On the sticker in the doorway on the driver's side (the recommended tire sizes are also indicated there).
- 🔧 In the electronic spare parts catalog (for example, ETKA for VW/Audi or EPC for Mercedes).
Services like Diski.ru, Koleso.ru or WillTheyFit.com allow you to enter the make, model and year of manufacture of your car - and get a list of compatible parameters, including ET. Please note: some services show range of acceptable values, but it is better to stick to the factory setting.
If the markings have worn off and there is no documentation, you can measure ET manually. For this you will need:
- 📏 Ruler or caliper.
- 📐 Square (or any object with a right angle).
- 🧮 Calculator.
To measure yourself, follow the instructions:
Remove the disc from the vehicle and clean the mating surface|
Place the disc face down on a flat surface|
Attach the square to the rim and measure the distance from the mating plane to its edge (parameter A)|
Turn the disk over and measure the distance from the mating plane to the opposite edge (parameter B)|
Calculate the offset using the formula: ET = (A + B)/2 – B-->
For example, if A = 120 mm, and B = 100 mm, then:
ET = (120 + 100)/2 – 100 = 10 mm.
⚠️ Attention: When measuring, keep in mind that even a small error (1–2 mm) can critically affect the result. For accuracy, use a caliper rather than a regular ruler.
Permissible deviations ET: when you can deviate from factory standards
Car manufacturers always indicate optimal reach, but in some cases slight deviations are allowed. However, there are strict limitations:
- 🔧 For production cars: deviation from factory ET acceptable within ±3 mm. For example, if it is recommended ET45, you can install disks with ET42–ET48 without serious consequences.
- 🚘 For tuned cars: when installing wider rims, it is sometimes necessary to reduce the offset (for example, with ET45 up to ET35), so that the wheels do not touch the arches. In this case necessarily required:
- 🔹 Check the gaps at maximum turning of the steering wheel.
- 🔹Install spacers (if the offset decreases by more than 10 mm).
- 🔹 Adjust wheel alignment.
- ⚙️ For SUVs and crossovers: here the tolerances are a little wider - up to ±5 mm, but only on condition that the car is not operated at high speeds (more than 140 km/h).
Important: even if the deviation is within the tolerances, be sure to check:
- 🔹 Do the wheels touch brake calipers or shock absorbers.
- 🔹 Hasn’t it changed? straight line stability (the car should not “steer” to the side).
- 🔹 Haven’t they appeared? vibrations on the steering wheel during acceleration.
If you are installing wheels with a shorter offset (for example, to widen the track), be sure to check compatibility with stepped bolts or nuts. Sometimes longer fasteners are required to securely secure the disc.
Common mistakes when choosing ET disks and how to avoid them
Even experienced car owners sometimes make mistakes when selecting wheels based on their offset. Here are the most common ones - and how to prevent them:
- Ignoring the ET parameter when purchasing used disks.
Many people buy wheels “by diameter and bolt pattern” without checking the offset. For example, disks from Volkswagen Passat (ET45) externally fit Skoda Octavia, but if on Octavia factory ET38, then the difference is 7 mm will lead to accelerated wear of the suspension.
- Installation of disks with “universal” ET.
Some sellers position discs with ET35–ET40 as “suitable for most cars”. In fact, such a flight may be optimal only for Japanese Domestic Market (JDM)-cars, but not at all suitable for European models (for example, BMW 5 Series often requires ET20–ET25).
- Neglect of spacers when changing ET.
If you install wheels with a shorter offset (for example, to widen the track), but do not use spacers, then wheel alignment is disturbed. This leads to:
- 🔹 Steering wheel beating at speed.
- 🔹 Uneven tire wear.
- 🔹 Increased load on wheel bearings.
Another common mistake is buying disks by appearance, and not by parameters. For example, disks with ET15 visually look more aggressive due to the wide track, but if your car is designed for ET45, then such a replacement will lead to:
- 🔹 Increase lever of force on the suspension (on 30–40% higher load on silent blocks).
- 🔹 Offset center of gravity wheels, which impairs handling.
- 🔹 Risk wheel separation in case of a strong side impact (for example, off-road).
What happens if you install wheels with ET 20 mm less than recommended?
With this deflection, the wheels will move outward by 20 mm on each side, which is equivalent to an increase in track by 40 mm. Consequences:
✅ Visually, the car will look wider and “meaner”.
❌ The load on the wheel bearings will increase by 1.5–2 times, which will lead to their failure after 10–15 thousand km.
❌ The risk of wheels hitting the arches will increase when fully loaded or on uneven surfaces.
❌ Handling at high speed will deteriorate due to a change in the rolling shoulder.
❌ It is possible for wheels to touch elements of the brake system (for example, calipers on sports cars).
ET and tuning: how to safely change offset for wide rims
Many car owners want to install wider wheels to improve appearance or improve stability. However, along with the width, it is often necessary to adjust the offset. Here's how to do it safely:
- Calculate the permissible deviation.
For most cars maximum permissible reduction in ET - this is 15–20 mm from the factory value. For example, if the original departure ET45, then the minimum acceptable is ET25–ET30.
- Use spacers.
If the offset decreases by more than 10 mm, be sure to install centering spacers. They compensate for misalignment and maintain proper wheel alignment. Spacers are:
- 🔹 Flat (for small ET changes).
- 🔹 Stepped (for significant displacements).
- 🔹 With additional holes for bolts (if PCD needs to be increased).
On sports and tuned cars (for example, Golf GTI or BMW M3) are often installed large brake calipers. Decrease ET may cause the disc to touch the caliper. In this case you will need discs with undercuts or spacers.
Example of safe tuning:
- 🚗Car: Toyota Camry V50 (factory ET45).
- 🔧 Desire: install disks with width 9J instead of 7.5J.
- ✅ Solution: select disks with ET30 + spacers 15 mmto compensate for the offset.
- ⚠️ Check: make sure that:
- 🔹 The wheels do not touch the arches when the steering wheel is turned completely.
- 🔹 The length of the bolts is sufficient for reliable fixation.
- 🔹 The work has not changed ABS and ESP.
When tuning ET offset, always follow the following rule: 1 mm change in offset ≈ 1 mm displacement of the wheel outward or inward. For example, reducing the ET from 45mm to 30mm will move the wheel 15mm outward on each side, increasing the track by 30mm.
ET and safety: why you shouldn’t skimp on departures
Some car owners deliberately ignore this parameter ET, considering it "minor". However, the consequences of such savings can be extremely serious:
- 🚨 Risk of wheel coming off.
If there is a significant departure deviation (more than 20 mm) changes force application vector to the hub. This may lead to loosening of fastening and even wheel coming off while driving, especially when driving over uneven surfaces.
- 🚨 Deterioration in controllability.
Incorrect ET displaces center of gravity wheels, which leads to:
- 🔹 Yaw car at speed.
- 🔹 Delayed reaction to turn the steering wheel.
- 🔹 Increased braking distance (due to changes in load distribution).
- 🚨 Increased wear on the suspension.
Even a slight departure deviation by 5–10 mm increases the load on:
- 🔹 Wheel bearings (lifetime is reduced by 30–50%).
- 🔹 Suspension arms and silent blocks.
- 🔹 Steering rack (backlash appears).
It is especially dangerous to ignore ET on cars with air suspension (for example, Mercedes S-Class, Audi A8). Here, even a minimal shift in the center of gravity of the wheels can lead to incorrect system operation and loss of control.
⚠️ Attention: On vehicles with all-wheel drive (for example, Subaru Impreza, Mitsubishi Lancer Evolution) an incorrect departure can cause increased vibration due to imbalance in the transmission. In severe cases this leads to differential failure.
FAQ: Frequently asked questions about ET crash on disks
Can I install rims with ET35 instead of ET45?
Technically it is possible, but it will move the wheels outwards by 10 mm on each side. Consequences:
- 🔹 The load on wheel bearings will increase.
- 🔹 It is possible to touch the arches when fully loaded.
- 🔹 Controllability at high speed will deteriorate.
Recommended to use spacers 10 mmto compensate for the offset.
Which ET is better for a lowered car?
On lowered vehicles (for example, stance projects) often install disks with negative ET (for example, ET-5 or ET-15) so that the wheels “stick out” outward. However, this is fraught with:
- 🔹 Rapid wear of the suspension.
- 🔹 Risk of touching the arches.
- 🔹 Deterioration of exchange rate stability.
The best option is to keep the factory ET and use narrow tires with a low profile.
Does ET affect speedometer readings?
No, ET does not affect the speedometer, as it does not change wheel circumference. However, if along with departure you change rim diameter or tire profile, the speedometer readings may become inaccurate.
Is it possible to drive with different ET on the front and rear axle?
Absolutely not! Different offsets on the axles lead to:
- 🔹 Unpredictable handling (the car may “steer” to the side).
- 🔹 Increased wear of the transmission (on all-wheel drive vehicles).
- 🔹 Risk of skidding during sudden braking.
The exception is some sports cars (for example, Porsche 911), where the factory provides different ET on the front and rear axles.
What is the ET of wheels for UAZ Patriot?
For UAZ Patriot (depending on the year of manufacture) factory offset is:
- 🔹 ET40–ET45 for stamped discs.
- 🔹 ET35–ET40 for alloy wheels (depending on width).
Permissible deviation - ±5 mm. When installing discs with ET20–ET25 (to expand the track) be sure to use spacers and check compatibility with the brake system.