Wrong. disk-out, indicated in the marking as ET, leads to accelerated wear of hub bearings and friction of the inner edge of the tire against the suspension elements. Immediately after installing the wheels with an incorrect parameter, the driver may notice a change in steering behavior and the appearance of extraneous noise when cornering. Ignoring the factory specifications of the car manufacturer often causes the suspension units to fail long before their lifespan expires.
Parameter Einpress Tiefe (German abbreviation ET) defines the distance between the vertical plane of symmetry of the wheel and the plane of application of the disk to the hub. This value is measured only in millimeters and can have a positive, negative or zero value. Understanding the physical essence of this size is necessary for every car owner who plans to replace regular wheels with cast or forged analogues.
Physical meaning and geometry of the departure parameter
The geometry of the wheel is built around several key points, and disk-out It is one of the most important coordinates in this system. Imagine a disc lying flat: the plane that divides its width exactly in half is called the plane of symmetry. It is from this imaginary line that the countdown to the landing plane is carried out, which contacts the hub of the car during installation.
If the landing plane is shifted outward relative to the center of the disk, then the departure is considered positive. This configuration is most common on modern front-wheel drive cars, where compact placement of the wheel inside the arch is required. In the case when the mounting point is closer to the inner part of the disk or even outside the central axis, the departure becomes negative, which is typical for off-road vehicles and tuned cars with a wide track.
- 📏 A positive ET means that the disc is “recessed” deep into the arch, pressing against the hub with the outside.
- 🚜 Negative ET pushes the wheel outwards, significantly expanding the track of the car and changing its visual appearance.
- ⚖️ Zero departure indicates that the mounting plane coincides with the central axis of the disk.
It is important to understand that changing this parameter directly affects the shoulder of the run-in and the load transferred to the suspension. Even a visually minor change in geometry can create a critical lever of pressure on the mounting nodes.
Effect of ET deviations on suspension and steering
The designers of the car calculate the suspension parameters taking into account the specific loads that arise during movement. Disc launch This is a key lever here. When installing wheels with a smaller departure (the disc protrudes outward), the shoulder of the run-in increases, which leads to an increase in the load on the hub bearing. The bearing begins to work in overload mode, which reduces its service life many times.
⚠️ Warning: Installing drives with departures that differ from the standard by more than 5-7 mm can lead to the destruction of the hub and the loss of the wheel at high speed.
In addition, the change in departure affects the work of shock absorbers and Silentblocks. The suspension levers are at an unnatural angle, which causes their accelerated wear. Steering also responds to changes: the load on the steering rack and tips increases, vibration on the steering wheel may appear and the car may be taken away during braking.
Owners often wonder why you can’t just put the drive “wider.” The fact is that when reducing the departure wheel is shifted outward, and when turning the steering wheel, the outer part of the tire or the disc itself can begin to touch the arch of the body or suspension elements. Not only does this damage the paintwork and rubber, but it can also block the wheel in motion.
Permissible deviations and computation of compatibility
Many motorists believe that there is a strict tolerance, for example, ± 5 mm, but the real picture is more complex. Permissible deviation depends on the design of a specific suspension, the stiffness of the springs and the safety margin of the hub assembly. For some models of cars, even a deviation of 2 mm can be critical, while others will “forgive” and 10 mm.
When calculating compatibility, it is necessary to take into account not only ET, but also the width of the disk. The formula is simple: when the disk width increases by 1 inch (25.4 mm), the outlet should decrease by about half of this value to keep the inner edge of the disk in the same place. If this is not done, the disc will start to rest on the brake caliper or suspension elements from the inside.
| Parameter | Effect of increasing the value | Effect of diminution | Criticism |
|---|---|---|---|
| ET (Getaway) | The wheel goes deeper into the arch | The wheel extends outwards | Tall. |
| Disk width | Increased contact spot | Track narrowing and sustainability | Medium |
| DIA (Diameter) | Reduce the tyre profile | The risk of arching | Tall. |
| PCD (Shatting) | Impossibility of installation | Impossibility of installation | Critical |
There is a myth that the use of spacers for disks completely solves the problem of departure. Stakes They do change the geometrical flight, but they also increase the load on the studs or mount bolts. The lengths of the regular bolts may not be enough for reliable fixation, which requires the purchase of elongated fasteners.
Formula for calculating departure change
If you change the width of the disk, use the rule: new ET = old ET - (new width - old width) / 2. This will help keep the internal geometry of the wheel unchanged.
How to read the label on the disk
To determine disk sizeYou don’t have to be a design engineer. All the necessary information is stamped on the inside of the spokes or on the rim of the disk. The marking looks like a set of numbers and letters, for example: 7.5 J x 16 H2 ET35 5/112 DIA 66.6.
In this line, we are interested in the meaning after the letters. ET. In the example above, the flight is 35 millimeters. This means that the landing plane is offset from the center of the disk by 35 mm towards the outer surface. If the number is preceded by a minus sign (for example, ET-15), then the flight is negative.
- 🔍 Look for the inscription.
ET,EinpressorOffseton the back of the disk. - 📐 The number next to the designation indicates a value in millimeters, the + sign is usually not put.
- ⚠️ The absence of departure markings on new discs is a sign of counterfeit products or the danger of buying.
Sometimes the marking can be hidden under a layer of paint or dirt, so before buying used discs, they should be thoroughly cleaned. The lack of clear labeling should alert the buyer, since it is impossible to determine the parameters by eye.
When buying discs online, always require a photo marking on the inside. Sellers often post only a photo of the front, hiding the real parameters of ET.
Consequences of Ignoring Factory Parameters
Ignoring the manufacturer’s recommendations in pursuit of an exclusive design often results in financial losses. Wrong takeoff causes uneven wear of the tire tread, especially if the wheel touches the suspension elements during compression. This not only wastes money on new tyres, but also worsens traction in critical situations.
The most dangerous consequence is a change in the kinematics of the suspension. In an emergency, with a sharp maneuver or braking, a wheel with an inappropriate departure can behave unpredictable. Increased departure can lead to the fact that the wheel rests in a spar or shock absorber, which is fraught with an accident.
⚠️ Note: Insurance companies may refuse to pay compensation if the examination establishes that the cause of the accident was the installation of non-standard wheels.
It is also important to remember the legal side of the issue. Changes in the design of the vehicle, which include the installation of wheels with parameters that do not meet the requirements of the manufacturer, may be the basis for prohibiting the operation of the car. When passing a technical inspection, such inconsistencies are easily detected.
☑️ Checking before buying discs
Frequent questions and misconceptions of motorists
Around the parameter. fly-out There are a lot of myths. One of the most common ones is that “a big departure is always better” because the wheel sits deeper. This is not true: an excessively large departure can lead to the fact that the inner part of the disc or tire will begin to rub against the shock absorber rack or elements of the brake system.
Another misconception concerns the universality of pads. Many people think that a 20 mm space will solve all the problems with the appearance. However, such a prostrate turns even a moderate positive flight into a near-zero or negative one, which radically changes the load on the suspension. Stack bearing It works in the extreme modes.
Some drivers believe that if the disc physically fits on the hub and the bolts twist, then everything is fine. That's a dangerous misconception. Visual compatibility does not guarantee the proper operation of the car’s nodes under load. Suspension geometry is an exact science where every millimeter counts.
The Golden Rule: The ideal drive is one whose parameters are completely consistent with the recommendations of the car manufacturer. Any deviations are a compromise that must be technically justified.
Can I put ET40 drives instead of ET45s?
The 5mm difference is often within the range of what is acceptable for many cars, but not for all. It is necessary to check whether the disc will not touch the caliper from the inside and whether the wheel will not get out too much, touching the arch. It is best to consult with technical experts for your particular model.
How does the flight affect the crossover?
For SUVs, drives with a smaller departure (or negative) are often used to expand the track. This increases the stability of the car on the slopes and prevents getting stuck in the ruts. However, this increases the load on the transmission and requires the installation of arch extenders.
Does the flight affect fuel consumption?
Yeah, it's indirectly. The increase in departure (the wheel protrudes outward) worsens the aerodynamics of the car, creating additional air swirls around the wheel arches. This can lead to a slight but noticeable increase in fuel consumption over long distances.
What happens if you confuse the right and left disk with different departures?
Discs with directional or asymmetrical design are often labeled Left/Right. If you confuse them, the visual effect will be disrupted, but technically, if the PCD and DIA match, the car will drive. However, if the discs have different departure design (a rare case for one model), this will lead to the car being sidelined.