Choosing wheels is not just a matter of aesthetics or a desire to make a car look more beautiful. This is a complex engineering task, the correct solution of which depends on the safety of the driver, passengers and other road users. Incorrectly selected geometry can lead to the destruction of the hub bearing, damage to the suspension elements or even an emergency at high speed.
Unlike buying a flavouring or covers, you can’t rely on visual appeal alone. Each parameter specified in the product label is critical. Before you go to the store or study the catalogs of online sites, you need to clearly understand what parameters your car needs, and why deviations from them are unacceptable.
There are many myths that “if the disc climbed on the hub, then it will fit.” That's a dangerous misconception. Modern cars are designed with the most accurate load calculations, and even a minimum discrepancy. departure parameters The diameter of the system can disrupt the operation of stabilization systems and ABS. Let’s discuss all aspects of the choice in detail.
Basic parameters of wheel disc marking
Any disc, whether it's stamped stamp alloy castingIt has a standardized marking. It is usually struck on the inside of the spoke or on the rim. Reading this information is the first skill you need to learn. A typical marking looks like this: 7.5J x 16 H2 5/112 ET35 d66.5. Every number and letter here is not random.
The first number, in our example 7.5, denotes the width of the rim in inches. It depends on the width of what rubber can be mounted on the disk. The letter J indicates the shape of the rim edge, which is important for the reliability of the tire fixation. The next number, 16, is the diameter of the disk in inches, which should correspond to the landing diameter of the tire.
Particular attention should be paid to the alphanumeric code. 5/112. It's PCD (Pitch Circle Diameter)The number of holes under the fastener and the diameter of their location. Here, the error is unacceptable: if there are 5 holes and you need 4, the disk will not physically stand up. If the number coincides, but the diameter of the hole is different at least 1-2 mm, the nuts will be twisted with distortion, which will lead to spontaneous unwinding of the wheels.
⚠️ Note: The use of transition rings (settles) to modify PCD is strongly discouraged. Such designs disrupt the centering of the wheel and can lead to vibrations and destruction of the fastener on the go.
The last important parameter is the diameter of the central hole, denoted as d or DIA. In the example, it's 66.5 mm. This size should be equal to or greater than the diameter of the car hub. If the hole in the disk is larger, centring rings are used. If less, the disc simply will not be put on the ledge of the hub.
Disk Departure (ET) and its Effect on the Suspension
Parameter ET (Einpress Tief in German classification) or simply relegation, is one of the most insidious. It indicates the distance in millimeters from the plane of attachment of the disc to the hub to the vertical plane passing through the middle of the width of the rim. Many motorists mistakenly believe that you can safely change the departure in a larger or smaller direction for the sake of appearance.
The manufacturer shall calculate the suspension, steering and braking system for a specific departure. Changing this parameter shifts the center of gravity of the wheel relative to the suspension axis. This creates an additional load shoulder on the hub bearing. Even a small deviation can reduce the life of the bearing at times, causing its hum and destruction after several thousand kilometers.
In addition, the change in departure affects the kinematics of the suspension. With too small a flight (the disc "stick" outwards), the load on the steering elements increases, and with too large (the disk is "sunk" deep), the wheel can touch the internal elements: shock absorber, caliper of the brake or lever elements when compressing the suspension.
Permissible departure deviations
It is believed that the departure deviation within ± 5 mm is acceptable for most passenger cars, but this is only true for wide-profile tires and a calm driving style. For crossovers and SUVs, tolerances are stricter.
There is a formula for calculating the permissible departure, but it is best to adhere to the recommendations of the car manufacturer. If you still decide to change the standard departure, remember the rule: the wider the disk, the more you can vary the departure, but only in the negative side (reduce ET) to maintain the overall track, although this increases the load on the suspension.
Diameter, width and choice of rubber
The diameter of the disk directly affects the comfort and dynamics of the car. Installation of larger diameter discs (e.g., R17 instead R15) if the overall outer diameter of the wheel is maintained, the use of low-profile rubber shall be required. This improves the course stability and "sharpness" of the steering wheel, but makes the suspension stiffer.
The width of the disc should correspond to the width of the tire. There are standard tables of conformity, which indicate on the disks what width can be mounted tires of a certain width. Using a too narrow disc for a wide tire will cause the sidewalls of the rubber to “bubble”, worsening the control. Too wide a disc for a narrow tire can cause the rubber to break off the rim in a turn.
When increasing the diameter of the disk, it is important to take into account the gaps in the arches. When the suspension is compressed or when the wheels are turned to their extreme position, the wheel shall not touch the bodywork or the underwings. This is especially true for cars with clearance close to the minimum, or after installing non-standard springs.
When switching to larger diameter discs, be sure to check whether they will touch the caliper of the brake system. Many modern cars have large brakes, and the inner spoke of the disc must have a sufficient departure or a special shape.
It's also worth remembering. wheel-diameter. If you change the dimensions of the discs, you need to recalculate the tire profile so that the wheel diameter remains within the permissible 2-3% of the factory. Otherwise, the speedometer readings will be lying, and the ABS and ESP systems may not work properly.
Manufacture materials: stamps, cast and forged
The choice of material is always a compromise between price, weight, strength and appearance. The market offers three main types of disks, each of which has its own characteristics of operation and maintenance.
- 🛑 Stamped discs: They are made of sheet steel by the method of stamping and welding. They are heavy, prone to corrosion and look rustic, but are characterized by high maintenance and low price. Ideal for harsh winter conditions, when the roads are sprinkled with reagents.
- 💎 Cast discs: Produced from aluminum alloys by injection molding method. They are lighter than dies, have many designs and better remove heat from the brakes. However, they are fragile: with a strong impact on the curb or in a hole, the cast disc can crack, rather than bend.
- ⚔️ Forged discs: The most expensive and technological option. They are made by the method of hot bulk stamping. They have high strength (bent, but do not crack) and minimal weight, which has a positive effect on the dynamics of acceleration and fuel consumption.
It is important to understand that “casting” requires a more careful attitude. Recovery of the cast disc geometry is possible, but it is a complex and expensive process requiring argon welding and painting. Steel disc can be straightened with a sledgehammer in any garage service for pennies.
For the winter period of operation, many experts recommend having a separate set of discs smaller than in summer. This will allow the use of rubber with a higher profile, which will improve the passability and soften the impacts on the irregularity of frozen asphalt.
Compatibility and calculation table
To systematize the data and understand how the parameters change during selection, consider an approximate table of the dependence of the disk width on the width of the bus. This will help to avoid mistakes when buying.
| Tyre width (mm) | Min. disk width (inches) | River. disk width (inches) | Max. disk width (inches) |
|---|---|---|---|
| 195 | 5.5 | 6.0 - 6.5 | 7.0 |
| 205 | 6.0 | 6.5 - 7.0 | 7.5 |
| 215 | 6.0 | 7.0 - 7.5 | 8.0 |
| 225 | 6.5 | 7.0 - 7.5 | 8.5 |
| 235 | 7.0 | 7.5 - 8.0 | 9.0 |
Using this table, you can see if your current drive is suitable for new rubber or vice versa. Remember that placing a tire on a disc of inappropriate width changes the contact spot with the road, which affects the braking distance and handling.
☑️ Checking before buying discs
Fastening and additional elements
Often when buying new discs, fasteners are forgotten. Bolts or nuts for steel and alloy discs may differ in length and shape of the clamping pad. For stamps, a cone is used, for many cast disks - a sphere or a plane. Using an inappropriate fastener will cause the wheel to not press evenly.
The length of the bolt is also critical. If you take a short bolt from the stamp for a cast disk, it may not reach the thread in the hub. If you take too long - it will rest in the brake mechanism or touch the handrail cable, which will cause creaking and jamming of the wheel.
Centering rings (spare) are necessary if the diameter of the central opening of the disc is larger than the diameter of the hub of the car. They are made of plastic or aluminum and ensure the wheel fits accurately. Without them, all the load falls on the bolts, which causes the steering wheel to vibrate at high speeds.
⚠️ Warning: Never use a sealant or glue to fix center rings. They should sit tight due to the accuracy of the dimensions. Any movement of the ring will cause the wheel to beat.
Visual fitting and final check
Before paying for a purchase, especially if it is made not in a specialized center, but “with hands” or in the market, a visual fitting is required. Even if all the numbers in the label are the same, the actual geometry may differ due to the design features of the spokes.
Apply the disc to the hub (without rubber). Check if it sits freely on the central hole. Try to insert bolts - they should enter without distortion. If possible, screw the disc and twist it with your hand, checking the gap to the caliper and suspension elements.
The main principle of selection: geometric compatibility is more important than appearance. A beautiful disc that cannot be safely operated will only be an expensive piece of jewelry in a garage.
It is also worth inspecting the disk for hidden defects: microcracks in the welding sites (for composite disks), chipped paint, which can become foci of corrosion. For cast discs, it is important to check for hidden deformations that may not be visible to the eye, but will cause a beat.
Frequently Asked Questions (FAQ)
Can I put 4x100 PCDs on a car that should be 4x98?
Theoretically, a difference of 2 mm in diameter might seem insignificant, and the wheel might be “tightened.” However, this will lead to the fact that when tightening the bolts, the disk will get distorted. As a result, one hole will be pressed tightly, and the opposite will hang out. This will cause severe vibrations, uneven wear and risk of spinning the wheel. You can't do that categorically.
How to find out the departure of the disk if the marking is erased?
Visually determine the flight is impossible. It is only possible to estimate approximately how much the disc is sunk or bulges relative to the arch, comparing it with the factory sample. The exact flight can be measured only with the help of a special tool (line and flat bar) or find out by the catalog number of the disk on the Internet, if it is preserved.
Does the weight of the disk affect fuel consumption?
Yes, it does. Wheels are rotating masses. Reducing the weight of each wheel (especially around the periphery) reduces the moment of inertia. The engine requires less energy to spin the wheels, which has a positive effect on the dynamics of acceleration and, to a lesser extent, on fuel consumption. Forged discs are lighter than cast, and cast ones are lighter than stamped.
Do I need to balance after installing new disks?
I will. Even the new disc has an acceptable factory imbalance. When installing rubber, this imbalance is added up. Balancing with the use of loaders is necessary to eliminate vibrations and extend the life of the suspension. Neglect of this stage is unacceptable.
Can I use the sleeves to change the flight?
The use of paddles up to 5-10 mm thick is permissible if the wheel studs allow the wheel to be securely fixed. The larger thickness of the drawers requires replacement of the regular bolts with longer ones or the use of studs with studs.