Selection of wheels for a car is not only a matter of aesthetics, but also a critical technical procedure, on which traffic safety directly depends. Many motorists, seeking to improve the appearance of the car, often focus solely on the design and diameter, forgetting about the geometric parameters that should perfectly coincide with the suspension units.
One of the most common mistakes is to ignore the exact size and location of the mounting holes. The mismatch between these parameters can lead to the wheel beating at speed, the destruction of the hub bearing or even the wheel breaking off during movement.
In this article, we will discuss in detail what PCD, DIA and ET are, how to correctly measure the distances between holes and why using slots requires special attention to the specifications of the disk.
What is PCD and how does it affect disk installation
abbreviation PCD Pitch Circle Diameter (Pitch Circle Diameter) refers to the diameter of the circle along which the centers of the fastening holes of the disk are located. This is perhaps the most important parameter that should strictly match the specification of your car. Even a minimal deviation in a larger or smaller direction will make the disk installation impossible or dangerous.
In the labeling of the disc, this parameter is usually indicated after the diameter and width. For example, a recording 5x114.3 This means that the disc has 5 holes located on a circle with a diameter of 114.3 millimeters. If you try to place a PCD 114.3 disk on the hub of PCD 112, one of the bolts will simply not get into the hole, and the rest will be skewed.
There is a common misconception that a difference of 1-2 millimeters can be compensated by force or the use of bolts with a misaligned head. This is a dangerous practice, since with dynamic loads on corners or when braking, the geometry of the mount will be broken, which will lead to the unbalance of the wheels.
- 🔧 Standard PCD values: The most common are 4x100, 5x112, 5x114.3 and 6x139.7, but there are more than a dozen variations.
- 🔧 Precision of manufacture: tolerances in the production of discs are minimal, so "eye-tracking" is unacceptable.
- 🔧 Safety impact: PCD mismatch causes uneven distribution of load on the fastener.
⚠️ Attention: Never try to stretch holes or use bolts of inappropriate length to make up for the difference in PCDs – this is a direct path to an emergency on the road.
Diameter of the central hole (DIA) and the centering rings
Parameter DIA (Diameter) or dA is the diameter of the central hole that is worn on the hub of the car. Ideally, this size should exactly match the diameter of the hub protrusion. It is the central hole, not the bolts, that takes over the bulk of the loads when moving, ensuring the precise centering of the wheel.
If the diameter of the hole on the disc is larger than the hub protrusion, the wheel will only hold due to the bolts. This will lead to the fact that with the slightest weakening of the fastener, the wheel will begin to "walk", causing vibrations of the steering wheel and body. In such cases, special centreringThey fill the gap between the disc and the hub.
The situation where the central hole of the disc is smaller than the diameter of the hub is less common, but it is also possible when buying universal or non-original discs. In this case, mechanical swelling of the hole is permissible, but only if there are sufficient metal bars to maintain the strength of the structure.
Material of the centering rings
Plastic rings are used for discs that do not experience extreme loads, and perform the function of simple centering. Light alloy or steel rings are used in sports motorsport and on heavy SUVs, where the rigidity of the connection and heat removal from the brake system are important.
When buying cast or forged discs, pay attention to the configuration. Often manufacturers offer universal discs with a large DIA, where the rings are nested in the kit. The loss of these rings can turn the process of seasonal rubber replacement into a problem requiring an urgent search for analogues.
Disk Output (ET) and its Interaction with Geometry
Although the disk is out (ET or Offset) is not the size of the hole, it directly affects how the disc will stand relative to the arches and suspension elements. The departure is the distance between the vertical plane of the disk symmetry and the plane of application of the disk to the hub. It's measured in millimeters.
When changing the departure, the shoulder of the run-in changes, which affects the load on the bearings of the hub and the suspension. If you put the drive with a departure less than the standard (the disk protrudes outward), the load on the suspension increases, and the wheel can begin to touch the arch when compressed.
On the contrary, a disk with a large departure (recessed deeper) can touch the brake caliper or elements of the levers. This is especially critical for cars with multi-link suspension and large brake mechanisms.
☑️ Checking disc compatibility
- 📏 Positive departure: The mounting plane is shifted from the center of the disk (standard for most passenger cars).
- 📏 Zero departure: The mounting plane coincides with the disk symmetry axis.
- 📏 Negative departure: The plane of attachment is shifted to the outside (characteristic of SUVs and tuning).
PCD compatibility table of popular brands
For quick orientation in the variety of parameters of the drill, it is useful to know the standards used by various automakers. While there may be exceptions within a single brand, especially when changing platforms, the main trends are clear.
Below is a table with the most common PCD values for different vehicle classes. Remember that the number of holes is also a key factor: 4 holes are more common on subcompact cars, and 5 or 6 on crossovers.
| Make/Class of Auto | Number of holes | PCD (mm) | Note |
|---|---|---|---|
| VAZ (Lada), Oka | 4 | 98 | Classic front-wheel drive drill |
| BMW, Mercedes (old models) | 5 | 112 | One of the most common standards |
| Toyota, Honda, Nissan, Mazda | 5 | 114.3 | Asian Standard for the Middle Class |
| UAZ, GAZ, American SUVs | 5 or 6 | 139.7 | It is often found as 5x139.7 or 6x139.7. |
| Ford Focus (old), Volvo | 4 or 5 | 108 | European Platform |
The use of data from the table is relevant for the initial selection, but before buying Always check your vehicle’s VIN code.Because depending on the year of release and configuration parameters may differ. For example, some Ford models have switched from a 4x108 drill to a 5x108.
How to measure the parameters of the disk
If the labeling on the disk is erased or in doubt, the parameters can be measured independently. To do this, you will need a calculator or ruler with high accuracy, as well as a calculator or knowledge of geometry. Measuring the number of holes (4, 5, or 6) is obvious, but determining the diameter of a circle (PCD) requires calculations.
For a disc with 4 holes, it is enough to simply measure the distance between the centers of opposite holes. This will be the PCD you want. It is more difficult to have an odd number of holes, for example, 5 or 3. Here the distance between the centers of two adjacent holes is measured, and the resulting value is multiplied by a special coefficient.
For 5 holes, the coefficient is 1.701, and for 3 holes - 1.155. The formula looks like this: PCD = Distance between adjacent holes * Coefficient. The accuracy of the measurement should be high, as the difference between the standards (e.g. 100 mm and 98 mm) may not be visible to the eye, but is critical when installed.
When measuring PCD with a ruler, try to measure from the inner edges of the holes, and then add the diameter of the hole itself to get the distance between the centers more accurately.
⚠️ Attention: When measuring the diameter of the central hole (DIA), make sure that you measure the clean hole without taking into account the chamfers or decorative elements that can distort the actual landing size.
Disk Discs: When They Are Needed and Are They Dangerous?
Wheels are metal plates mounted between the disc and hub to change the departure (ET) or adapt a disc with an inappropriate PCD. They allow wider discs or drives from other cars to be installed, but their use must be strictly justified.
There are spacers that simply push the disk away (change ET), and complex adapters that change the drill. The second are considered less reliable, as they add an extra connection point and increase the load shoulder on the hub bearing. The use of slots thicker than 20-30 mm often requires replacement of regular bolts with longer studs.
The quality of the material of the paddles is crucial. Cheap Silumin products can burst under load. It is recommended to use aerospaces made of aluminium or steel, which have passed quality control. When installing paddles, it is necessary to regularly check the tightening of bolts, since the risk of self-unwinding increases.
The shelves change the geometry of the suspension and increase the load on the bearings, so their installation must be consistent with the permissible limits for your car model.
FAQ: Frequently Asked Questions
Can I place a PCD 114.3 disk on hub 112?
Theoretically, using eccentric bolts (with a floating cone part) is possible, but is highly discouraged for everyday use. This solution is considered temporary and requires constant monitoring of tightening. It is better to choose discs with the correct PCD.
What happens if the diameter of the central hole (DIA) of the disk is larger than the hub?
The wheel will not be centered. The entire load will fall on the bolts, which will lead to their rapid weakening, vibrations at speed and potential destruction of the fastener. Make sure to use transition rings.
Does the size of the holes affect the inspection?
Formally, at the inspection, the backlashes and the beat of the wheel are measured. If the disc is installed through the spacers or with a discrepancy of the PCD so that there is a visible beat or backlash, the car will not pass the diagnosis. Visually, the drill is usually not checked unless there are obvious signs of a "kolkhoz".
How to know the departure (ET) of the disk if the inscription is erased?
It is difficult to calculate ET independently without disassembling the disk. You need to know the total width of the disk, the distance from the landing plane to the inner edge and to the outer edge. Formula: ET = (A1 - A2) / 2where A1 and A2 are the distances from the mounting plane to the edges of the disk.