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Wheel parameters
How to read alloy wheel parameters?
Choosing alloy wheels is not just about appearance. Every rim must comply with the vehicle’s technical requirements to ensure safety, proper handling, sufficient load capacity, and trouble-free installation. That is exactly why the markings stamped or cast on the wheel are so important.
On this page, we explain all the key alloy wheel parameters: width, diameter, ET, PCD, CB, J flange profile, H2 rim contour, load capacity, and additional markings. This will make it easier for you to assess whether a given wheel will actually fit your car.
Where are the markings located on a wheel?
In the case of alloy wheels, the markings are usually found on the inner side of the spokes, near the center bore, or on the inner barrel of the rim. This placement helps maintain the clean appearance of the wheel face.
On the rim, you may find either a full sequence of markings or individual symbols placed in different areas. When buying used wheels, it is worth reading them carefully, because they are what allow you to verify whether the product matches the vehicle’s technical requirements.
The most important parameters you need to understand before buying
Wheel markings are a practical set of technical data. Reading them correctly helps you avoid mounting issues, steering wheel vibrations, rubbing against the wheel arch, improper tire seating, or overloading the rim.
ET
Defines wheel offset and affects how deeply the wheel sits in the wheel arch.
PCD
Defines the number of mounting holes and the diameter of the circle they are arranged on.
CB
Responsible for proper centering of the wheel on the hub.
J and H2
Describe the flange design and rim contour, which are important for tire installation.
Example of a full wheel marking
The notation below contains the key information needed to verify a wheel:
| Marking element | Meaning |
|---|---|
| 8.0 | Wheel width in inches |
| J | Wheel flange profile |
| 18 | Wheel diameter in inches |
| H2 | Double hump in the rim contour |
| ET35 | Wheel offset of 35 mm |
| 5x112 | Bolt pattern: 5 holes on a 112 mm circle |
| CB66.6 | Center bore diameter of 66.6 mm |
| Max Load 690 kg | Maximum permissible load of one wheel |
Explanation of all alloy wheel parameters
Each of the parameters below has a real impact on how the wheel fits the vehicle. Some are responsible for mounting to the hub, others for compatibility with the tire, and others still for safety under load and during everyday driving.
Wheel width – the first parameter in the marking
Wheel width is the first dimension in the marking, e.g. 7.5 or 8.0. It is given in inches and refers to the distance between the inner bead seats of the rim, which is where the tire is mounted.
The wheel width is used to select the correct tire width. A tire that is too narrow or too wide in relation to the rim can worsen handling, affect tread wear, and make correct installation more difficult.
| Wheel width (inches) | Recommended tire width (mm) |
|---|---|
| 6.0 | 175–195 |
| 7.0 | 195–215 |
| 8.0 | 215–235 |
| 9.0 | 235–255 |
| 10.0 | 245–275 |
J – wheel flange profile
The letter that appears directly after the wheel width, e.g. 7.5J, defines the flange profile. In passenger cars, the most common profile is J, while in SUVs and off-road vehicles JJ is also frequently used.
The flange profile matters for proper tire seating and airtightness. Not every tire fits every flange type, so rims and tires intended for different profiles should not be mixed.
| Symbol | Application |
|---|---|
| J | Passenger cars |
| JJ | SUVs and off-road vehicles |
| B | Older passenger cars |
| D, E, F | Commercial vehicles, motorcycles, machinery |
Wheel diameter – rim size for the tire
Wheel diameter is the number that appears after the flange profile marking, e.g. 16, 18, or 20. It is given in inches and indicates the internal tire diameter the rim was designed for.
This parameter must match the tire size. For example, a tire for an 18-inch wheel must have an inner diameter corresponding exactly to an 18-inch rim. There is no tolerance range here — the size must match exactly.
H, H2, EH2+ – wheel contour profile
Markings such as H, H2, FH2, or EH2+ describe the rim contour profile, meaning the internal shape of the area where the tire is seated. This mainly refers to the number and type of so-called humps that prevent the tire from slipping off.
In modern passenger car wheels, H2, meaning a double hump, is very common. In the case of run-flat tires, EH2 or EH2+ profiles are particularly important.
| Symbol | Meaning |
|---|---|
| H | Single hump |
| H2 | Double hump – the most common type |
| FH2 | Double flat hump |
| EH2 / EH2+ | Extended hump, used for example with run-flat tires |
ET – wheel offset
ET (Einpress Tiefe) means the distance between the wheel’s mounting surface and the geometric centerline of its width. This parameter is given in millimeters, e.g. ET35.
It is one of the most important dimensions because it determines how deeply the wheel will sit in the wheel arch. Too low an ET can push the wheel outward, while too high an ET can move it too far inward. In both cases, there is a risk of worse handling, rubbing against the wheel arch, or affecting the suspension geometry.
| ET value | Mounting effect |
|---|---|
| ET > 0 | Wheel sits deeper in the wheel arch |
| ET = 0 | The mounting surface aligns with the centerline of the wheel |
| ET < 0 | Wheel protrudes further outward |
Example: if the car has a factory ET35 and you install an ET15 wheel, the rim will move outward by 20 mm. This may improve the appearance, but at the same time increase the risk of rubbing and place more load on suspension components.
PCD – bolt pattern
PCD (Pitch Circle Diameter) defines the wheel mounting pattern on the hub. The notation consists of two elements: the number of mounting holes and the diameter of the circle on which they are arranged. For example, 5x112 means 5 holes on a circle with a diameter of 112 mm.
PCD must be identical to the vehicle specification. Even a small difference means the wheel will not fit properly. Attempting to install a rim with a different bolt pattern may damage the hub, bolts, and create a serious safety risk.
| PCD marking | Meaning |
|---|---|
| 4x100 | 4 mounting holes on a 100 mm circle |
| 5x112 | 5 mounting holes on a 112 mm circle |
| 5x120 | 5 mounting holes on a 120 mm circle |
| 6x139.7 | 6 mounting holes on a 139.7 mm circle |
CB – center bore diameter
CB (Center Bore), sometimes also marked as CH, is the diameter of the wheel’s center bore. This opening works together with the hub centering lip and is responsible for the correct seating of the rim.
If the center bore is larger than the hub, hub centric rings are required. If it is smaller, wheel installation is impossible. An incorrectly matched center bore can cause wheel runout, steering wheel vibrations, and accelerated suspension wear.
| Wheel CB | Mounting condition |
|---|---|
| Equal to hub diameter | Perfect fit |
| Larger than hub diameter | Hub centric rings required |
| Smaller than hub diameter | Installation impossible |
Max Load – maximum wheel load capacity
Wheel load capacity is most often given directly in kilograms next to the Max Load marking. This parameter is especially important in heavier vehicles: SUVs, electric cars, station wagons, and vehicles operated under higher loads.
The minimum load capacity of one wheel should not be lower than half of the load on the heavier axle of the vehicle. In practice, this means that if the rear axle has a permissible load of 1700 kg, each wheel on that axle should have a load capacity of at least 850 kg.
Additional markings that are also worth knowing
Other data may also appear on the wheel, helping you assess its intended use, vehicle compatibility, and the level of safety during operation.
KBA number
The KBA number is a homologation marking found especially on wheels intended for the German market. It indicates that the rim model has been approved for use and may matter during roadside inspections or technical inspections in selected markets.
ECE, TÜV, ABE, and other homologation markings
You may also find markings related to homologation and quality testing on the wheel or in its documentation. For the user, this is valuable information that the rim has been checked for compliance with technical requirements, safety, and legal use in specific markets.
Why is it so important to read wheel parameters correctly?
Safe installation
A wheel with the correct PCD, CB, and diameter fits the hub and works with the tire according to the manufacturer’s specifications.
Proper vehicle handling
The correct ET and rim width affect suspension geometry, stability, and driving comfort.
Lower risk of vibrations and rubbing
Correctly matched parameters help avoid steering wheel wobble, improper wheel centering, and tire contact with the wheel arch.
Fit for the vehicle’s weight and character
In modern SUVs and electric cars, wheel load capacity, rim contour profile, and compliance with the manufacturer’s requirements are especially important.
What should you check before buying alloy wheels?
- Check the wheel width and diameter against the tire.
- Verify the ET to avoid rubbing and geometry issues.
- Make sure the PCD is identical to the vehicle specification.
- Compare the CB with the hub diameter and use hub centric rings if necessary.
- Pay attention to the J/JJ and H2/EH2+ profiles, especially with non-standard setups and run-flat tires.
- Check the Max Load, especially for heavier vehicles.
Choose your wheels wisely and without guessing
Understanding alloy wheel parameters helps you avoid costly mistakes and choose rims that will not only look good, but above all work safely with your car.