Choosing wheels is one of the first things you deal with on a car, and also one of the easiest to get wrong. Just one wrong number and the wheel rubs against the fender, you feel vibration on the highway, or your car fails inspection.

The good news is that it's all about five values: bolt pattern, center bore, offset (ET), width, and diameter. Once you understand them, you'll choose wheels without guessing and without unpleasant surprises. Let's go through them in order, including what actually applies in Slovakia for MOT and registration in the technical certificate.

01How to read wheel and tire dimensions

Before you start choosing anything, it's worth knowing how to read what you already have on your car. A wheel usually has a size embossed on it that looks something like this: 8.5J x 18 ET35 5x120. The number 8.5J is the wheel width in inches, 18 is the diameter in inches, ET35 is the offset in millimeters, and 5x120 is the bolt pattern, meaning five bolts on a circle with a diameter of 120 millimeters.

A tire has its own marking, for example 225/40 R18. The number 225 is the tire width in millimeters, 40 is the aspect ratio, meaning the sidewall height as a percentage of the width, and R18 is the diameter, which must match the wheel diameter. If you can read and understand these two lines, most of the work is done, and the rest is just about making sure the numbers match each other and your car.

02Bolt pattern and center bore: numbers that must match

These are two values for which there is no compromise. They either fit, or you simply cannot mount the wheel on the car.

Bolt pattern (PCD)

The bolt pattern, or PCD, tells you how many bolts the wheel has and on what diameter circle they are spaced. It is written, for example, as 5x112, which means five bolts on a circle with a diameter of 112 millimeters, and it must be accurate to the millimeter. In practice, for example, a large proportion of VW, Audi, Škoda, and Seat vehicles use 5x112, BMW uses 5x120, although newer models have switched to 5x112, many Japanese cars including Nissan use 5x114.3, and older cars like the Honda Civic or Mazda MX5 use 4x100. You can find your bolt pattern in your technical certificate, on the original wheels, or in a catalog by make, model, and year of manufacture.

Center bore diameter (hub)

The center bore is the hole in the center of the wheel that sits on the wheel hub and carries the weight of the car. If the bore is smaller than the hub, you cannot mount the wheel. If it's larger, which is common with aftermarket wheels, the wheel is not centered, and you must use hub centric rings. Without them, you will feel vibration at higher speeds, which people often mistake for poorly balanced wheels.

03ET, or offset, and car stance

ET is the value around which most debates revolve, and rightly so, because it determines how the car looks and whether it will rub. Simply put, ET indicates how far the wheel's mounting surface is from its central axis. A lower ET moves the wheel further out towards the fender edge, which is called poke, and a higher ET tucks it deeper under the fender.

The following table illustrates the principle. Specific values vary from car to car, so use it as a guide, not as exact numbers for your model.

If you want to get the wheel further out, you go for a lower ET or help yourself with a thin spacer. If your wheel rubs the fender from the outside, you need the opposite direction, i.e., a higher ET, a narrower tire, more negative camber, or fender flares. Never solve it with just one number; it always works as a whole.

04Wheel width, tire, and stretch

A certain range of tire widths fits one wheel width. When you stretch a narrower tire onto a wider wheel, it creates what is called a stretch, meaning a tensioned tire with the sidewall pulled inward at an angle. It is popular in the stance and drift scene because it helps avoid rubbing against the fender and gives a distinctive look. If, on the other hand, you primarily drive on the road and want comfort and grip, opt for a fuller profile. Therefore, you always choose the wheel and tire width according to what you want from the car, whether it's everyday driving, track, or drift.

05Why the wheel rubs and how to fix it

Most problems with new wheels revolve around rubbing. When your wheel rubs after installation, the first step is to find out exactly where, because the solution from the outside and the inside is completely opposite. On lowered cars, there is less space in the fender, so adjustable suspension and correctly set geometry also play a role. Here's a quick guide to help you determine the cause.

• Rubs the fender from the outside: you need a higher ET, narrower tire, more camber, or fender flares
• Rubs the shock absorber or suspension from the inside: a lower ET or a thin spacer will help
• Rubs only during greater compression: check ground clearance and suspension travel
• You feel vibration at speed: likely missing hub centric rings or the wheel is poorly centered

If you're dealing with rubbing after lowering, check out our suspension and axle parts, where you'll also find spacers and components for fine-tuning geometry.

06MOT and registration of wheels in the technical certificate

This is a part that should not be taken lightly, as it can spoil an otherwise successful build. When you change the size of your wheels compared to what is recorded in your documents, it generally applies that the new size must be approved or homologated for the vehicle, and the change is registered in the technical certificate. During the technical inspection, the technician primarily checks whether the wheel does not protrude from the fender and whether it does not rub during full suspension compression and full steering lock.

That's why it makes sense to opt for parts with certificates and technical assessments, as they will significantly facilitate approval and registration. For each part in our offer, we state whether it has a certificate, so you know in advance what to expect during inspection. Conditions change over time, so always verify the final size with a technician before installation; this will save you time and money.

07Frequently asked questions