Incorrectly selected parameters PCD or departure ET can lead to the fact that the wheel does not physically fit on the hub or begins to rub against the suspension elements already within the first kilometers of driving. That is why deciphering the markings of alloy wheels is a critical step before purchasing, since the visual similarity of the models often hides technical differences that are incompatible with your car. Manufacturers apply a set of alphanumeric codes to the inside of a spoke or rim that determine the geometry of the product, its load capacity and compatibility with specific car models.
Ignoring this data is fraught not only with accelerated wear of the hub bearings, but also with the risk of the wheel coming off at high speed due to mismatched mounting holes. Understanding what each number in a line like this means 8.5Jx18 H2 5/112 ET35 d66.6, allows you to avoid costly mistakes and problems with the traffic police when registering a vehicle. Below we will analyze in detail each element of this formula so that you can accurately read the technical data sheet of the wheel.
Basic design and bore diameter
The first number in the marking, for example, 8.5 in the example above, indicates the width of the rim in inches. This parameter directly affects the width of the tire being installed: a disk that is too narrow will stretch the rubber profile, making the car roll, and one that is too wide can lead to the formation of “hernias” on the sidewall of the tire when it gets into a hole. For each rim width there is a recommended tire width range, violation of which will change the contact patch and handling characteristics.
Letter J indicates the shape of the rim flange where the tire seats. In the passenger car industry, profile J is standard, while SUVs sometimes have options JJ or K, which have different shelf angles. Although the difference may not be noticeable visually, using a non-standard profile may result in a leaky tire bead and loss of pressure.
⚠️ Attention: The seat diameter (number 18 in the example) must strictly correspond to the diameter of the tire. Installing R17 tires on an R18 wheel is physically impossible, but even the slightest discrepancy of a fraction of an inch (for example, using an industry standard instead of an automotive one) is unacceptable.
Symbol H2 indicates the presence of humps - special annular protrusions on the rim flanges. Their job is to keep the tubeless tire in place during sudden pressure drops or lateral overloads. If the disc is marked H (one hump) or H2 (two humps), this guarantees safe operation with modern tires. Absence of humps (denoted as FH or flat profile) is typical for vintage cars and does not fit most modern low profile tires.
Mounting system: PCD drilling
Parameter PCD (Pitch Circle Diameter) is one of the most important and often ignored indicators when selecting non-original discs. In marking it looks like a fraction, for example, 5/112 or 4/98. The first number indicates the number of mounting holes, and the second number indicates the diameter of the circle on which they are located, in millimeters. Even a slight deviation in drill diameter (eg 1-2mm) will result in the nuts or bolts not being tightened to the correct torque.
Using adapter rings or eccentric bolts for adjustment PCD allowed only by certified manufacturers and only in extreme cases. Ideally, the geometry of the holes should match to within tenths of a millimeter. If the holes on the disc and the hub do not match, the wheel warps relative to the axis of rotation, which causes the steering wheel to wobble and body vibration at speeds above 60 km/h.
- 🔩 4/98 - standard for many models FIAT, LADA, ALFA ROMEO.
- 🔩 5/112 - the most common standard for the group VAG (Volkswagen, Audi), Mercedes-Benz and BMW.
- 🔩 5/114.3 - popular size for Toyota, Nissan, Honda, Mazda and Korean brands.
- 🔩 6/139.7 - typical for frame SUVs and pickups (Toyota Land Cruiser, Nissan Patrol).
When visually inspecting the disk, it is important to check the quality of the holes. Factory markings are often applied near the drill bit, but sometimes you have to look for them on the inside of the spokes. If you buy used wheels, make sure that the holes are not worn out or ellipsed due to driving with loose bolts.
Disc offset (ET) and its effect on suspension
Parameter ET (Einpress-Tiefe) or Offset indicates the distance between the plane of attachment of the disk to the hub and the vertical plane passing through the middle of the rim width. It is measured in millimeters and can be positive, zero or negative. Most front-wheel drive vehicles are characterized by positive offset, when the mounting plane is offset outward relative to the center of the disc.
A change in offset relative to factory recommendations is permissible within 5 mm, up or down. Reducing the offset (the disc becomes “wider” relative to the hub) causes the wheel to protrude from the arch, increasing the track and improving stability, but creating increased load on the hub bearings and suspension components. Increasing the offset can cause the inside of the rim or the tire itself to start rubbing against the brake calipers or shock absorber components.
| Parameter | Designation | Unit of measurement | Impact on the car |
|---|---|---|---|
| Departure | ET / Offset | mm (mm) | Wheel position in the arch, bearing load |
| Width | J | inches | Contact patch width, tire profile |
| Diameter | R / D | inches | Wheel outer diameter, speedometer readings |
| Sverlovka | PCD | mm + quantity | Possibility of physical installation on the hub |
When installing wheels with an offset different from the standard one, be sure to use a torque wrench to tighten the bolts to the torque recommended by the car manufacturer, and check the tightening after the first 50 km.
Center hole (DIA) and centering rings
The diameter of the central hole, denoted as DIA, D or CO, must be equal to or (most often) greater than the diameter of the landing collar on the car hub. In the marking it looks like d66.6 or DIA 73.1. It is through this shoulder that the main torque is transmitted and vibrations are damped, and not through the mounting bolts.
If the diameter of the hole on the disk is larger than the hub shoulder (for example, a disk with d73.1 on a car with d66.6), centering of the wheel occurs only due to the taper of the bolts or nuts. This is acceptable, but less reliable and can lead to beats. To solve this problem, plastic or metal centering rings, which fill the gap between the disc and the hub, providing ideal rotation geometry.
In the case where the central hole of the disk is smaller than the diameter of the car hub, boring the disk is strictly prohibited, as this violates the integrity of the alloy and can lead to destruction of the wheel. In such a situation, the disk simply will not fit your car, and no adapters will help here.
⚠️ Attention: Never operate a vehicle without centering rings if the disc hole diameter is larger than the hub diameter. The absence of rings will cause vibration of the steering wheel at high speeds and accelerated wear of the fasteners.
Load capacity and quality standards
Each cast disc has a maximum load that it can withstand. This parameter is marked as MAX LOAD and is indicated in pounds (lbs) or kilograms (kg). For example, the inscription MAX LOAD 690 kg means that one wheel can carry up to 690 kg. The total load of four wheels must exceed the total curb weight of the vehicle with passengers and cargo with a safety margin of at least 20-25%.
To confirm safety, disks undergo certification. In Europe the standard is TÜV, in Russia - compliance with GOST or availability of an EAC certificate. Japanese wheels are often marked VIA or JWL. The absence of these signs may indicate handicraft production, where casting technologies and quality control were not followed, which makes the operation of such products dangerous.
Difference between JWL and VIA
JWL is a mandatory Japanese standard for passenger cars, while VIA is a more stringent standard for light trucks and SUVs. The presence of both logos indicates a high safety margin of the disc.
The disc may also contain the date of manufacture. It is often stamped with numbers indicating the week and year of production (e.g. 12/23 - 12th week of 2023). Although aluminum does not have an expiration date like rubber, knowing the date allows you to assess whether the disc was stored in improper conditions for a long time, which could affect the condition of the paintwork and the structure of the metal.
Practical recommendations for selection
When choosing new discs, always rely on the data specified in the technical documentation of your car, and not on the advice of sellers or “universal” tables on the Internet. Parameters may vary even within the same model depending on the year of manufacture, engine type and configuration. The best way to avoid mistakes is to remove one of the stock wheels and read the markings on the inside.
If you plan to install larger diameter wheels (for example, moving from R16 to R18), you will need to recalculate the tire profile so that the overall outer diameter of the wheel remains the same. Changing the wheel diameter will affect the speedometer readings, the operation of the ABS and ESP systems, and can also lead to the wheel arches touching when the car is fully loaded.
☑️ Check before purchasing a disc
Usage original discs or certified analogues from well-known brands (OZ Racing, BBS, Enkei, K&K) guarantees compliance with all geometric parameters. Cheap Chinese replicas often have deviations in the parameters of spoke thickness and casting quality, which, if they fall into a deep hole, can lead to a chip or crack, while a high-quality disc will only be dented.
Can discs with a different number of holes (PCD) be used?
No, that's impossible. The number of holes must match strictly. There is no legal or safe way to change the number of mounting holes on a wheel or hub. Attempts to drill new holes destroy the structure of the disc.
What happens if the offset (ET) differs from the standard one by 10 mm?
A deviation of 10 mm is considered significant. This will lead to a change in the rolling shoulder, an increase in the load on the wheel bearings, and possible interference with the wheel arches or suspension elements. In some cases, this may cause refusal to register a vehicle.
Are centering rings required for alloy wheels?
Yes, if the diameter of the central hole of the disk is larger than the diameter of the car hub. Without rings, the wheel will not be perfectly centered, causing vibration. If the hole is smaller, the disc simply will not fit onto the hub.
How often should I check the tightness of bolts on alloy wheels?
It is recommended to check the tightness of bolts or nuts after the first 50–100 km of driving on new discs, since during this period the initial shrinkage of the metal occurs. Next, the check is carried out at each seasonal tire fitting or scheduled maintenance.