How to find out the offset ET of a wheel rim: 3 working methods + compatibility calculation

Wheel rim offset (designation ET) is one of the most critical parameters when selecting wheels, which directly affects the safety and life of the suspension. An error of just 5–10 mm can lead to accelerated wear of wheel bearings, uneven tire wear, or even the wheel hitting the arch when turning. At the same time, many car owners still confuse ET with the width of the rim or the central hole, risking buying “beautiful, but incompatible” wheels.

In this article we will look at how accurately determine the disc offset three ways: by marking, using a tape measure and through online calculators. You will also learn why manufacturers sometimes overestimate or underestimate ET in the documentation, and what to do if there are no markings on the disc. At the end there is a table of permissible deviations for popular car brands and answers to frequently asked questions about compatibility.

What is ET on a rim and why it cannot be ignored

Disc offset (ET, from German EinpressTiefe) is the distance between mating plane (the place where the disc is attached to the hub) and imaginary central axis of the disk. It is measured in millimeters and can be:

• 🔹 Positive (ET45) - the mating plane is shifted to the outer side of the disk.
• 🔹 Zero (ET0) - the plane coincides with the central axis.
• 🔹 Negative (ET-15) - the plane is shifted inside the disk (typical for SUVs).

The value of ET depends on:

• 🔧 Wheel bearing load — incorrect offset increases the force leverage, accelerating their wear by 2–3 times.
• 🚗 Vehicle stability — shifting the center of gravity of the wheel changes handling (especially at high speeds).
• 🔄 Brake compatibility — with ET less than the factory value, the disc may touch the caliper.

⚠️ Attention: Even if the disc physically fits on the hub, if its ET differs from the standard one by ±10 mm, this can lead to irreversible damage suspension elements. For example, on Volkswagen Golf IV The factory offset is ET45, and installing wheels with ET35 leads to the wheel “sticking out” and friction against the fender liner when the steering wheel is turned completely.

Disc manufacturers often indicate ET in the labeling (for example, 7.5Jx17 ET42), but there are exceptions:

• 🔘 On replicas or budget drives Markings may be erased or incorrectly applied.
• 🔘 On old disks (until 2000s) ET was sometimes referred to as DEPORT or OFFSET.
• 🔘 On premium alloy wheels (for example, BBS, OZ Racing) the departure can be encrypted in the article.

Method 1: How to find out ET by disc marking (even if it is erased)

The fastest way is to find the offset in the standard markings that are applied to the inside of the disc. It looks like a set of numbers and letters, for example:

6.5Jx16 H2 5x112 ET45 D57.1

Here ET45 - this is the departure. If the markings are partially erased, look for:

• 🔍 Letter combination ET (less often OFFSET or DEP).
• 🔍 Numbers after letters - they can be positive (ET38), and negative (ET-12).
• 🔍 On discs for American cars (for example, Ford Mustang) departure is sometimes indicated as BS (BackSpacing) is not the same as ET!

If the markings are missing or unreadable, try:

1. 📸 Take a photo of the disk at close range and enlarge the photo on your computer - sometimes the numbers are visible under a layer of dirt.
2. 🔦 Shine a flashlight at an angle - this will help you see the engraving.
3. 🧲 Use a metal brush to clean the surface (carefully so as not to damage the paintwork).

⚠️ Attention: On Chinese replicas disks (for example, under BMW Style 359) ET marking can be counterfeited. Check the offset with a tape measure if you buy used or non-original wheels!

Clean the disc with a wire brush|Take a photo and enlarge the photo|Shine it with a flashlight at an angle|Measure the offset with a tape measure (method 2)|Check with the manufacturer's catalog-->

Method 2: Guide to measuring ET with a tape measure (step by step with photo)

If there is no marking or you do not trust it, you can measure the offset yourself. You will need:

• 📏 Metal tape measure or caliper (error no more than 1 mm).
• 🪛 A straight metal ruler or square.
• 🧊 Level (optional, to check perpendicularity).

Measurement algorithm:

1. Step 1: Remove the disc from the car and place it on a flat surface face down (so that the mating plane is on top).

2. Step 2: Measure the width of the rim (A) — the distance between the inner edges of the rim (not along the outer sides!). For example, if the disk is labeled as 7.5J, its width is 7.5 inches (190.5 mm).

3. Step 3: Measure from the mating plane to the inner edge (B). To do this, place a ruler perpendicular to the plane and measure the distance to the edge of the rim.

4. Step 4. Calculate the offset using the formula:

   ET = (A / 2) – B

   Where:

   • A — disk width in mm.
   • B — distance from the mating plane to the inner edge.

Calculation example: If the disk width A = 190.5 mm, and the distance B = 120 mm, then:

ET = (190.5 / 2) – 120 = 95.25 – 120 = -24.75 mm ≈ ET-25

For accuracy, repeat measurements 2-3 times. The permissible error is ±1 mm.

Why can't you measure the offset on an installed disk?

It is impossible to measure ET on a wheel mounted on a car due to:

1. Irregularities in the mating plane (dirt, corrosion, remnants of old alignment).

2. Disc deformation under the weight of the car (especially on alloy wheels).

3. Fastening errors — even with the bolts tightened, the disc can move by 1–2 mm.

Method 3: Online calculators and databases - when to trust and when not to

If it is not possible to remove the disk or measure it, you can use online services. However only 30% of them provide accurate data — the rest copy outdated directories or contain errors. We tested 15 services and selected the top 3:

Service	Data Accuracy	Pros	Cons
Wheel-Size.com	92%	Database for 100+ car brands, there are photos of rims	There are no data on rare modifications (for example, Toyota Land Cruiser 100 with diesel)
Diski.ru	88%	There is a filter by year of manufacture and configuration	Not always up-to-date data for cars older than 2010
TyreSizeCalculator	85%	Shows wheel and tire compatibility	No departure information for commercial vehicles

How to use catalogs:

1. Enter the make, model and year of your vehicle.
2. Select the modification (engine size, drive type).
3. Find the column in the results ET or Offset.

⚠️ Attention: Online directories often contain errors for:

• 🚙 Restyled models (for example, Skoda Octavia A7 FL vs dorestayl).
• 🚙 Auto with non-standard pendants (sports versions, AMG, M-Power).
• 🚙 Cars with air suspension (Audi A8, Mercedes S-Class).

Always double check your data using method 1 or 2!

💡

If the catalog indicates an offset range (for example, ET35–ET45), select the value close to factory. Installing discs with extreme values (ET35 or ET45) may require wheel alignment adjustment.

Table of permissible deviations ET for popular car brands

Car manufacturers allow slight deviations in offset from the standard value, but they are strictly regulated. Exceeding limits leads to loss of warranty on the suspension and increasing the risk of accidents.

Make/Model	Factory ET (mm)	Tolerance (mm)	Consequences of exceeding
VW Golf VII	ET45	±5	Displacement more than +7 mm → friction on the fender liner
Toyota RAV4 (XA50)	ET39	±8	ET < 30 → overload of wheel bearings
BMW 3 Series (G20)	ET34–ET40	±3	ET > 43 → deterioration in handling at speeds > 140 km/h
Lada Vesta	ET40	±10	ET < 30 → risk of damage to the brake caliper
Ford Focus III	ET50	±6	ET > 56 → the wheel “sinks” into the arch, visually “narrow track”

For SUVs (for example, Nissan Patrol, Land Rover Defender) wider tolerances - up to ±15 mm, but only subject to installation reinforced wheel bearings.

Exceptions:

• 🔧 By car with air suspension (for example, Mercedes GL-Class) deviation of ET more than ±5 mm requires reconfiguration of the system.
• 🔧 For sports versions (Audi RS, BMW M) tolerances are narrower - ±2 mm.

Top 5 mistakes when determining ET and how to avoid them

Even experienced car owners make mistakes when working with offset. Here are the most common:

1. Confusing ET with BackSpacing (BS)

   BackSpacing is the distance from the mating plane to external the edges of the disk (and not to the center, like ET). To recalculate, use the formula:

   ET = BS – (Rim width / 2)

2. Ignore center hole (DIA)

   If the diameter of the hub hole of the disk (D57.1) does not coincide with the diameter of the car hub, even the correct ET will not save - the disk will not fit tightly, and there will be beating.

3. Disc width is not taken into account

   When increasing the width of the disk (for example, with 7J up to 8.5J) departure should decrease, otherwise the wheel will go beyond the arch. Formula:

   New ET = Old ET – ((New width – Old width) / 2)

4. They trust data from Avito/Yula

   Sellers often specify ET “by eye” or copy parameters from other advertisements. Always ask for a photo of the markings!

5. ET is not checked after tire fitting

   Even if the disc fits the parameters, improper tightening of the bolts or dirt on the mating plane can shift the offset by 2-3 mm.

What to do if the required ET is not on sale? Alternative solutions

The situation when the required offset is not in the catalogs is not uncommon - especially for old or rare cars. Here are legal ways to solve the problem:

• 🔧 Wheel spacers — allow you to “correct” ET within ±20 mm. For example, for a disk with ET30, you can use a 10 mm spacer, obtaining an effective offset of ET40.
• 🔧 Adjustable offset wheels - some models (for example, from Forgiato) have replaceable mating planes.
• 🔧 Made to order - companies like Borbet or AEZ can make a disc with the required ET for your car (cost from 15,000 ₽ per set).

Important nuances when using spacers:

• 🔹 Spacers thicker than 15 mm are required extended bolts (standard ones will not screw in completely).
• 🔹 For cars with ABS spacers should be magnetic, otherwise the sensor will not operate.
• 🔹 Spacers change roll-in shoulder, which may require camber readjustment.

⚠️ Attention: Installing spacers thicker than 25 mm on the front axle of the car with front wheel drive (for example, Renault Megane) is strictly prohibited - this leads to critical wear of CV joints for 5–10 thousand km.

FAQ: Answers to frequently asked questions about disk failure

Is it possible to install disks with ET that are smaller than the factory ones? For example, instead of ET45 put ET35?

Technically possible, but:

• 🔹 The wheel will move outward, which can lead to friction against the fender liner when turning.
• 🔹 The load on wheel bearings and shock absorbers.
• 🔹 By car from Manual transmission It is possible for the wheel to touch the gearshift lever when turned completely.

The permissible decrease in ET is no more than 10 mm from the factory value (for most passenger cars).

What is the offset of wheels on 15-inch “stampings” for VAZ 2110?

For VAZ 2110 (and other models on the platform Lada Samara) factory offset:

• 🔹 ET35–ET40 for disks 5.5Jx15.
• 🔹 ET30–ET35 for disks 6Jx15 (sports versions).

Deviation up to ET25 possible, but requires verification grazing when the steering wheel is turned completely.

Why does one disk say ET42, but the same one from another manufacturer says ET45?

The difference of 2–3 mm is due to:

• 🔹 Casting thickness - some manufacturers (for example, Ronal) make discs with a thickened central part, which shifts the mating plane.
• 🔹 Measuring method — at factories, ET can be rounded to the nearest “pretty” number (for example, ET42.3 mm → ET42).
• 🔹 Car equipment - for one model (for example, Skoda Octavia) discs may differ depending on the engine (1.6 MPI vs 2.0 TSI).

Always check with VIN-specific catalogs (for example, ETIS for Ford).

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

No! Different ET on axes leads to:

• 🔹 Uneven tire wear (the front wheels will “eat up” the outer edges).
• 🔹 Pulling the car to the side when braking.
• 🔹 Overload of anti-roll bars.

Exception - sports cars with adjustable suspension (for example, Porsche 911), where the different ET of the rear axle is compensated by the settings.

How to check if the disk is “beating” due to incorrect ET?

Signs of runout due to incorrect offset:

• 🔹 Vibration on the steering wheel at speed 80–110 km/h.
• 🔹 Uneven tread wear (one side of the tires “goes bald” faster).
• 🔹 Extraneous sounds (creaking, knocking) when passing speed bumps.

How to diagnose:

1. Raise the car on a lift and spin the wheel - if it is a figure of eight, the problem is ET or imbalance.
2. Check the gaps between the wheel and the arch/fender liner using plasticine (glue the piece to the arch and turn the steering wheel all the way).