The automotive industry has come a long way in the development of wheels – from steel to alloy, and even to magnesium or carbon fiber. This is an accessory that can completely transform the look of any vehicle. Wheels are one of the first things people notice on a car, and they often become a topic of discussion – whether it's about design, color, brand, fitment, or overall style. Properly chosen wheels can make a car stand out from the crowd or help it blend in better with a specific automotive community. However, choosing the right wheels isn’t just about aesthetics. It’s important to understand what each specification means and how it affects driving and vehicle compatibility. A poor choice can lead to wheels that don’t fit the car at all, stick out past the fenders, or rub against the suspension or brake components.

Basic terms when choosing wheels:

Tire dimensions and wheel dimensions are two different measurements. The size 225/45 R17 refers to the width, height, and diameter of the tire, not the dimensions of the wheel itself. Information and specifications for alloy or steel wheels are usually found on the inner side, in a format such as 7.6J x 17 ET13. We will explain all of these values in detail in this blog.

Wheel diameter:

Wheel diameter is given in inches and marked with the letter “R” before the number (standing for RADIAL), e.g., R16", R17", R18", and it indicates the overall size of the wheel. This value must match the diameter of the tires you plan to mount on the wheel. It’s generally true that larger wheels enhance the appearance of a car, but it’s important to keep in mind that the bigger the wheel, the more space it takes up in the wheel well. This can cause rubbing against the fenders or inner wheel arch lining. Larger wheels can also affect the functioning of the ABS system and the speedometer reading. However, with the correct tire size, it is possible to install larger wheels while maintaining the same overall rolling diameter.

For example:

Original wheel: 205/55 R16 (wheel 16")
New wheel: 225/45 R17 (wheel 17")
The overall diameter remains almost the same.

Upgrading to larger wheels also brings other issues that should be considered. Bigger wheels require lower-profile tires, which reduce shock absorption and negatively impact ride comfort. They are also heavier, which can slow down acceleration and slightly increase fuel consumption. Additionally, the larger the diameter, the higher the cost of both wheels and tires—resulting in greater overall expenses. The ideal solution is to choose wheels that were offered by the manufacturer for your vehicle model as standard or optional equipment. If a different trim level of the same car came with larger wheels, it’s highly likely that those wheels will fit your car without any issues. For tuning enthusiasts, the perfect combination with larger wheels is the installation of lowering springs or adjustable coilovers, which give the vehicle a more aggressive look and improve handling.

Wheel width:

It is also measured in inches (e.g., 7", 8", 9") and indicates how wide the wheel bed is – the area where the tire "sits". The correct width must match the width of the tires as well as the vehicle’s specifications. This dimension is often listed along with a letter (e.g., J), such as 7J, 8J, etc. The letter "J" refers to the shape of the bead seat – the edge of the wheel where the tire contacts the rim. This edge is technically called the "bead seat profile." There are other bead profile designations as well, such as K, JK, B, P, D, etc., which are typically used for trucks, vintage vehicles, or special applications. The differences between them lie in the exact curvature of the wheel’s edge. However, tires for regular passenger cars are typically compatible with the “J” profile as standard.

Each wheel width corresponds exactly to a specific tire size. Here are a few examples:

(Wheel width) 6.0" - 175 – 195 mm (tire width)
(Wheel width) 6.5" - 185 – 205 mm (tire width)
(Wheel width) 7.0" - 195 – 215 mm (tire width)
(Wheel width) 7.5" - 205 – 225 mm (tire width)
(Wheel width) 8.0" - 215 – 235 mm (tire width)
(Wheel width) 8.5" - 225 – 245 mm (tire width)
(Wheel width) 9.0" - 235 – 255 mm (tire width)
(Wheel width) 9.5" - 245 – 265 mm (tire width)
(Wheel width) 10.0" - 255 – 275 mm (tire width)

Besides regular use, it is possible to change the appearance of the vehicle by using tires of different widths.

If you want to achieve the “stretch” style, you need to mount a narrower tire on a wider wheel, which causes the tire sidewalls to stretch and creates an aggressive look for the whole setup. This style is mainly used on lowered cars, where the wide wheels need to fit precisely into widened fenders. However, it’s important to keep in mind that the tire no longer performs as it should and cannot function across its full range. This can lead to air leaks or damage (tearing) of the sidewall, which may result in serious consequences. For this reason, we do not recommend using this style for regular road driving.

Examples of "stretch" combinations:

(Wheel width) 8.0" - 195/40 R16 (tire width)
(Wheel width) 8.5" - 205/40 R17 (tire width)
(Wheel width) 9.0" - 215/35 R18 (tire width)
(Wheel width) 9.5" - 225/35 R18 (tire width)
(Wheel width) 10.0" - 225/40 R18 (tire width)

In the motorsport world, there is also the "meaty" style, which is the exact opposite of "stretch." In this case, the tire is wider or taller than what would be considered the correct size for the given wheel width. The tire isn’t stretched like in the stretch style; instead, the sidewalls are firm and bulging. This style is popular among performance cars, track-day builds, and off-road vehicles. A lower profile tire (e.g., 30 or 35) looks slim, while a higher profile (e.g., 45 or 50) creates a fuller appearance. This not only looks “meaty” but also improves comfort and protects the wheel from curbs. Advantages of this style include better grip and traction, increased comfort, and enhanced wheel protection. However, it’s important to watch out for tire rubbing against the wheel wells and distorted speedometer readings due to the different rolling diameter.

Examples of "meaty" combinations:

(Wheel width) 8.0" - 225/45 R17 (tire width)
(Wheel width) 8.5" - 245/40 R18 (tire width)
(Wheel width) 9.0" - 255/40 R18 (tire width)
(Wheel width) 9.5" - 265/35 R19 (tire width)

Offset (ET):

Offset (ET) indicates the distance between the wheel’s centerline and the mounting surface that contacts the hub. It is measured in millimeters and can be positive, negative, or zero. A positive offset (e.g., ET35) means the wheel is positioned further inside the fender. A negative offset (e.g., ET-10) means the wheel sticks out more from the fender. An incorrect offset can cause the wheel to either protrude beyond the fenders or be recessed too far inward. Both situations can affect driving dynamics, suspension geometry, and safety. The ideal fitment can be achieved by changing the offset or by using wheel spacers while keeping the original wheel dimensions. This allows the wheel to be pushed outwards from the hub slightly, which helps create an aggressive look and aligns the wheel’s outer edge with the fender, similar to race cars. Lower offset values also provide more concavity to the wheel design.

Practical example:

Stock wheel: 7.5Jx17 ET45
New wheel: 9.0Jx17
To maintain a similar fitment, it is necessary to reduce the offset: instead of ET45, you can use ET30 – ET35.

The wheel will stick out more towards the fender, but at the back it remains in the original position, so there is no risk of the wheel colliding with the shock absorber, brake caliper, or wheel arch liner.

Bolt pattern (PCD):

PCD (Pitch Circle Diameter) refers to the diameter of the circle that passes through the center of all the bolt holes on a wheel. It is usually expressed with two numbers separated by an "x". For example, 5×120 means the wheel has five bolt holes evenly spaced around a circle with a diameter of 120 millimeters. Similarly, 5×112 indicates five holes around a circle with a diameter of 112 mm. This specification is one of the most important when choosing the right wheel for your vehicle. However, it is usually not marked on the wheel or the hub itself. To find the exact bolt pattern, you should consult your vehicle dealer, the owner’s manual, or a wheel retailer who can assist you. Bolt patterns cannot be mixed, although there are some exceptions.

Wheel spacers for changing bolt pattern – as the name suggests, these spacers modify the bolt pattern of your vehicle to a different one, allowing you to use wheels from another vehicle with that specific bolt pattern. However, it is important to pay attention to the thickness of the spacer as well as the dimensions of the wheel.
Use of "floating bolts" – in this case, it is possible to fit 4x100 wheels onto 4x98 hubs without spacers, as bolts with a floating seating surface can compensate for the difference in bolt pattern.
Use of wheels with dual bolt patterns – these wheels have two sets of bolt holes, allowing them to be mounted on two different bolt patterns.

Center hole:

The center hole on the wheel rim and the wheel hub play a key role in the safe and proper mounting of the wheel on the vehicle. Although they are often overlooked in favor of parameters such as the bolt pattern (PCD) or offset (ET), the correct size and alignment of the center hole are essential for safety, stability, and ride balance. The center hole on the rim ensures precise centering of the wheel on the hub before tightening the bolts/nuts. If it does not fit exactly, eccentric mounting may occur, causing vibrations, uneven tire wear, and increased stress on components. Adjusting the center hole can be addressed in several ways.

Centering rings – Changing the center hole size can be achieved by installing centering rings or an adapter spacer. Available options include aluminum or plastic rings.
Spacer adapters with center hole modification – In addition to widening the track, these spacers also modify the center hole size, allowing wheels with a smaller center bore to be installed on vehicles with challenging fitment requirements.

Wheel load:

Wheel load (also known as load rating) indicates the maximum weight that a single wheel can safely support during operation. This value is usually expressed in kilograms (kg) and is either marked on the wheel itself (e.g., on the inside of the rim) or specified in the manufacturer’s technical specifications. If a wheel is rated for 500 kg, it means that the maximum allowable vehicle load on four such wheels is 2000 kg. A wheel that is not rated for the vehicle’s weight may deform, crack, or fail, especially when driving over uneven surfaces or during aggressive driving.

If you are unsure about the basic specifications of your vehicle, we recommend visiting the following websites, which can help you with both the bolt pattern and the specific fitment.

Bolt pattern, threads, offset, center hole - https://www.wheelfitment.eu/car/
Comparison of the fitment of original wheels versus new ones - https://www.willtheyfit.com/

Bolts and nuts:

Depending on the type of vehicle, bolts or nuts may be used to attach the wheel to the hub. Both types have their differences, including thread types and seating surfaces.

Bolts - M12x1,25; M12x1,5; M14x1,25; M14x1,5 are the most common types. They can also differ in the seating surface of the head – conical (60°), spherical, or flat.
Nuts - If the vehicle uses nuts, studs are installed in the hubs. Just like with bolts, there are thread types such as M12x1.25, M12x1.5, M14x1.25, and M14x1.5. The seating surfaces can also be conical (60°), spherical, or flat. When it comes to nuts, it is important to pay attention to whether they are open-ended or closed-ended.

Bolts and nuts can also have different outer diameters. Japan Racing requires narrow nuts and bolts for their wheels to fit through the narrow installation hole.

Wheel certification:

Certified wheels are approved for regular road use and have homologations such as ECE, KBA, ABE, TÜV, or JWL/VIA. These markings guarantee that the wheel has passed tests for strength, load capacity, and safety. However, it should be noted that many companies, such as BRAID or EVO Corse, focus primarily on high-level rally where certification is not required. Using uncertified wheels on public roads is illegal and can lead to issues during vehicle inspections (MOT), loss of warranty, or invalid insurance coverage in case of an accident. Motorsport wheels are designed for the track, not for the road – they are extremely lightweight but often lack certification, making them unsuitable for regular traffic.

Japan Racing Certificates - https://jr-wheels.com/tuv-certificates