The selection of wheels for a particular brand of car is not only the original look of the product. The main characteristics of the product are operational data, in particular, the possibility of applying the rim to a particular brand of car. Disk overhang is a conditional parameter that indicates the distance between 2 planes. One of them is the area of application of the disk to the hub, and the second is the plane of symmetry of the wheel.
Incorrectly selected departure leads to premature wear of the suspension, shock absorbers and other vehicle components. Reduced maneuverability and controllability of the vehicle, increased operating costs.
What are the opinions about the importance of offset in the wheelset selection process?
Trying to put into practice the knowledge gained in a driving school, beginners are interested in: “What is wheel offset and how to choose the right model?”. The answers are different, sometimes contradictory.
Driving experts believe that this parameter refers to the main characteristics of the rim and is individual for each of the sizes. According to the manufacturer's recommendations, the removal must correspond to the data specified in the passport for the car.
Deviation from the set values contributes to the manifestation of the following processes.
First, the value of the wheelbase specified by the manufacturer is violated. This is due to the fact that when changing a wheel, the points of application of forces are shifted in places:
- interface with the suspension (through the bearing);
- contact with the road patch.
In the process of movement, the higher the speed and the greater the difference between the set value of the departure and the actual value, the greater the amount of torque the suspension system has to cope with. Including the wheel bearing.
As a result of such an impact, loaded nodes and mechanisms that play the main role in the process of energy transfer, as well as those responsible for safety, operate in a critical mode (and wear out quickly).
Secondly, different offset parameters for one (or several) wheels affect the uneven distribution of the wheel load.
This phenomenon impairs the controllability of the vehicle. It is dangerous when driving a car, especially when transporting a significant amount of cargo.
Thirdly, a change in the normal mode of interaction between the mechanisms of the running gear leads to the malfunctioning of other systems of the unit.
Manufacturers believe that it is better if the maximum permissible error from a given parameter does not exceed 3-5 mm in each direction.
Wishing to receive a commission for the sale of goods, unscrupulous sellers are advised not to pay attention to a slight discrepancy.
With the application of a certain physical force, the disk with a slight deviation from the value given in the specifications can be fixed on the hub. If the rotation of the rim is not hindered by anything, it will work for some time.
How to determine the takeaway parameter?
The departure value is indicated by a pair of symbols - ET and is determined by the formula:
ET \u003d a-0.5v, in which:
a - the gap between the inner sphere of the disk and the space where the rim is attached to the hub;
c - disc clearance (width).
The value of ET can be different:
- positive;
- zero;
- negative.
In the first version, the design of the car provides for a greater degree of entry of the disk into the wheel arch. The offset value of zero corresponds to the position when the area adjacent to the hub coincides with the conditional plane passing through the center of the wheel rim. Discs with a negative offset differ from the rest in that the connection seat with the hub is deeply recessed into the rim. In this case, a significant part of the disk goes beyond the dimensions of the body.
Common labeling
According to international standards, the overhang value must be indicated on the inside of the disc. For countries with the metric system, the unit of measurement is the millimeter.
Designation example: ET0, ET30, ET-15. The last option indicates "-" overhang value, i.e. -15 mm.
