Where the offset is indicated on the discs: full explanation of the ET marking

Finding the exact geometric parameters of a wheel rim often turns into a quest for a car enthusiast, especially when it comes to departure. This characteristic is critical for safety, as it determines the position of the wheel plane relative to the hub. An error in calculations can lead to accelerated wear of the wheel bearings or even an emergency on the road.

Manufacturers put all the necessary information directly on the metal, but finding the right numbers can be difficult due to the abundance of other symbols. Unlike diameter or width, which are obvious, offset markings are often hidden among other numbers or printed on the inside of the spokes. Understanding exactly how ET affects the chassis, will help you avoid costly mistakes when purchasing.

In this material, we will analyze in detail where to look for the treasured numbers on stamped and cast models, and we will explain why you cannot blindly trust catalog data without visual verification. Disc offset is the distance in millimeters from the vertical plane of symmetry of the wheel to the plane of application of the disc to the hub. It is this parameter that dictates how much the wheel will be “recessed” into the arch or, conversely, protrude beyond its limits.

Explanation of the abbreviation ET and the physical meaning of the parameter

First, you need to understand the terminology so as not to confuse the concepts. On European and Asian-made discs, the offset is indicated by the abbreviation ET (from the German Einpress-Tiefe, which literally translates as “indentation depth”). In English-language documentation you can find the designation Offset, and in old Soviet catalogs the term “departure” sometimes appears, which can be positive, negative or zero.

Physically, this parameter represents the distance between the mating plane (that part of the disk that is pressed with bolts to the hub) and an imaginary vertical plane passing exactly in the middle of the rim width. If the mating plane is offset outward relative to the center of the wheel, the offset is considered positive. This is a standard situation for most civilian vehicles.

There are also discs with a negative offset, where the mount is shifted inward, towards the brake mechanisms. Such parameters are typical for SUVs and prepared jeeps, where a wider track is required for cross-country ability. Zero offset means that the mounting plane perfectly coincides with the central axis of the disk. Any deviation from the factory parameters changes the load vector on the suspension.

⚠️ Attention: Installing wheels with an offset that differs from the factory offset by more than 5 mm can lead to a change in the rolling shoulder, which will cause steering instability and accelerated tire wear.

Understanding this principle is important, since it is almost impossible to visually determine the difference between ET 35 and ET 45 by eye, but the consequences of operation will be radically different. Engineers calculate the suspension of a particular car, taking into account exactly those parameters that are included in the specifications.

Where to look for markings on cast and forged wheels

On light alloy wheels that are produced by casting or forging, manufacturers usually apply markings to the visible part of the spokes on the inside. This is the most accessible place that allows you to read information without removing the wheel from the car, although dismantling is still preferable for an accurate inspection. Look for a series of numbers embossed in relief or painted on.

Typical markings look like the sequence: 7.5J x 16 H2 ET 45 5x112. In this character set ET 45 and there is the desired departure. The numbers may be stamped separately from the rest of the row, sometimes on the back of one of the knitting needles. On expensive models BBS, OZ Racing or Enkei Markings can be done more neatly and placed in recesses of the design.

Sometimes, especially on models with complex shapes, the inscription may be upside down or positioned so that it is only visible from a certain lighting angle. It is recommended to use a flashlight and wipe the surface free of dirt before inspection. If you don't find the inscription ET, look for the word Offset or just a number after indicating the width and diameter.

What to do if the marking is erased?

If the paint on the disk has peeled off and the numbers are not readable, you can try to carefully clean the surface with fine sandpaper. However, if the disc was repainted or overcooked, the markings could be destroyed. In this case, the only reliable way is to measure the offset with a caliper or refer to the catalog data for the article number stamped on the inside of the hub.

It is important to distinguish the factory markings from the tire shop sticker. The adhesive label may indicate the parameters of the installed tires or the balancing date, but they are not a characteristic of the disc itself. You only need to focus on metal.

Features of markings on stamped steel disks

With stamped discs the situation is often more complicated. Due to the technological features of production and painting, the markings on the “stamps” may be covered with a layer of paint or located in hard-to-reach places. Most often, the numbers you are looking for are located on the inside of the central part of the disc, facing the brake caliper.

To see the markings, the wheel often has to be removed. Look for embossed numbers near the bolt holes or on the inside of the rim. The notation might look like ET 38 or Depression 38. On some domestic models, for example VAZ or GAS, the departure can be indicated simply by a number without letters, or the designation can be used Departure.

The problem with stampings is also that they are often subject to repair (editing). After severe impacts and subsequent rolling on the machine, the original geometry and markings may be distorted or destroyed. In such cases, relying on embossed numbers is dangerous.

• 🔍 Carefully inspect the back side of the central platform - the parameters are most often knocked out there.
• 🎨 A layer of paint can hide the numbers: carefully feel the surface with your finger or use the side light of a flashlight.
• 🛠 On old discs the markings may be (corroded), then only cleaning with a metal brush will help.

If you are buying used stamped wheels, the lack of a readable offset marking should be a reason to refuse the purchase or carefully check the dimensions at the bench. The risk of installing a wheel with the wrong offset is too great.

Full decryption of the disk marking string

In order not to get confused by the numbers, it is important to understand that each part of the code carries specific information. Let's look at a standard marking line with an example: 8.5J x 18 H2 5/112 ET 35 d 66.6. Knowing this structure will allow you to instantly find the desired parameter among many numbers.

First number (8.5) is the width of the rim in inches. Letter J denotes the shape of the rim flange (most common for passenger cars). Next number (18) — disk diameter in inches. Next comes an indication of the design (H2 - the presence of two humps, ring protrusions that hold the tubeless tire).

Parameter 5/112 indicates the number of mounting holes (5) and the diameter of the circle on which they are located (112 mm), this is the so-called PCD. And only after this data comes our ET 35. Completes the chain d 66.6 - the diameter of the central hole (DIA), which must perfectly match the hub or be larger (using spacer rings).

Parameter	Designation	Meaning	Units
Width	8.5J	Rim width	Inches
Diameter	R18	Bore diameter	Inches
PCD	5x112	Fasteners (holes/diameter)	mm/piece
Departure	ET 35	Disc offset	Mm
DIA	d 66.6	Central hole	Mm

Please note that the order of elements may vary depending on the manufacturer. Sometimes the departure is placed at the beginning of the line, sometimes at the end. The main thing is to look for a connection ET or Offset with a number.

Permissible deviations and influence on the suspension

Many car enthusiasts are wondering: is it possible to install wheels with a different offset? Short answer: you can, but within very narrow limits. Deviation is considered acceptable ±5 mm from the standard value. For example, if the factory recommends ET 40, then installing rims with ET 35 or ET 45 is generally safe.

When the offset changes, the rolling arm and the load on the suspension elements change. If the wheel moves outward (decreasing ET), the load on the wheel bearings and suspension arms increases. This happens because the vector of force from the weight of the car and inertia during turns is applied further from the axis of rotation.

In addition, a disc with a shorter offset may begin to touch the body arch when the car is fully loaded or when the steering wheel is turned. Conversely, a disc with a large offset (recessed deeper) may interfere with elements of the brake system or shock absorber. This is especially true for cars with calipers of complex shape.

If you are considering installing spacers, remember that they actually reduce wheel offset. Installing a 20 mm thick spacer on an ET 40 disc turns it into an ET 20 disc. This is a significant change that requires an intensive revision of the suspension condition.

How to measure disc offset yourself

If the marking is missing or in doubt, the offset can be calculated mathematically. To do this you will need a caliper (large), a ruler and a flat surface. The method is based on measuring two quantities: the overall width of the disk and the distance from the mating plane to the inner edge of the rim.

First, measure the overall width of the rim (not the tire!) in millimeters. Place the disc flat on a flat floor, mating side up. Place a ruler across the disc and measure the distance from the floor to the mating plane. This distance is half the width plus the offset (for positive ET).

The calculation formula looks like this: ET = A - B, where A - the distance from the mating plane to the inner edge of the rim (measured with the disk inverted), and B - half the total width of the disk. The resulting value will be the desired offset.

⚠️ Attention: When measuring the width of the disk, keep in mind that the actual width of the rim is always greater than the marked one (for example, 8.5 inches) by about 1-1.5 inches due to the characteristics of the edges. For calculations, use the measured actual width.

This method allows you to get precision down to the millimeter, which is quite enough to make a purchasing decision. However, if you are not confident in your measuring skills, it is better to entrust this work to the professionals at a tire center.

Frequently asked questions (FAQ)

What happens if you install a disk with an offset less than standard (for example, ET 20 instead of ET 40)?

The wheel will move significantly out of the arch. This will cause the tire to rub against the fender liner or arch when turning or loading the vehicle. In addition, the load on the wheel bearing will increase sharply, which can lead to its failure after 5-10 thousand kilometers.

Is it possible to compensate for offset with spacers?

Yes, spacers are installed between the disc and the hub and effectively reduce the offset. However, the use of spacers with a thickness of more than 20 mm requires replacing the standard bolts with longer ones or using studs, since the standard thread length may not be sufficient for reliable fastening.

Does offset affect speedometer readings?

The offset itself does not affect the wheel speed and speedometer readings, since the outer diameter of the tire remains the same. However, if due to a change in offset you are forced to install a tire of a different width or profile, then the readings may change.

Where exactly is the ET marking on BBS discs?

On disks BBS Markings are often applied to the inside of the spokes, closer to the rim. Sometimes it is written in very small font. On forged models of the series RS or RI the parameters can be stamped on the inside of the central part of the disk, hidden behind the cap.