Rims - All you need to know about bolt pattern, ET and sizes

2024-01-15

One of the quickest ways to change the look of your car is to replace old wheels with new ones. This can give your car a completely different feel and style, as well as making it more unique. Plus, a small upgrade can reduce the desire for a new car!

But it can be quite complicated with all the numbers and terms you need to know. For example, what does ET mean? And does the material matter? Let's find out!

Rim size is measured in inches

Rim size is one of the easiest things to figure out, as it is usually measured in inches. The most common sizes are somewhere between 18" (45.72 cm) and 20" (50.8 cm). One inch is equivalent to 2.54 cm, but for those who are unsure, most tape measures nowadays have centimetres as well as inches.

Bolt circle and bolt pattern

The rim's bolt pattern, or bolt circle as it is also called, indicates two things. One is how many bolts are needed to form a circle, and the other is the longest distance between the bolts - their diameter. The bolt pattern is written as '5x112' or '5/112'. The number 5 indicates how many bolts are needed. 112 is the diameter of the bolt circle in millimetres.

You need to know what your car's bolt pattern is when you buy new rims so that you buy ones that fit.

If you don't know your car's bolt pattern, you can measure it yourself. To begin with, count the number of bolts on the rim. If it's an even number (four, six or eight), measure the diameter from the centre of one bolt hole to the centre of the bolt hole opposite/across. This gives you, for example, 4/120 (4 bolts of 120 mm in diameter), so you should choose rims with that bolt pattern.

However, if you have an uneven number of bolts, you need to measure the diameter in a different way. This is because no bolt will sit exactly opposite another. In this case, you measure from the outer edge of a bolt hole to the centre of the bolt hole furthest from the "starting bolt".

ET, insertion depth and offset

"ET" is an abbreviation of the German word "Einpresstiefe" - "inpressing depth". It is called "offset" in English, but the term "ET" is often used in English as well. The ET measurement is the depth of compression, i.e. how much the centre of the rim protrudes. The measurement itself indicates how many millimetres from the centre of the rim the hub meets the rim.

A low ET value means that the rim comes further out, and a high ET value means that the rim sinks further into the wheel arch.

The ET measurement is engraved on the back of all rims. Check the dimensions of your current rims and choose the same when buying new ones.

Spacers

A spacer is a disc that helps the rim fit as well as possible into the wheel arch of the car by making it slightly wider. The rim comes out further towards the edge of the disc, giving it a lower ET measurement.

A good way to find out how wide the spacers can be is to measure. How much space is left between the tyre and the fender edge? The inner fender should not touch the car when it is heavily loaded.

Spacers can also be used to change the bolt circle if the rims have a different dimension than the car. This requires at least 15 mm thick conversion spacers, and you need to check that there is room for them along with the ET dimensions of the new rim.

It is important to check that the rim is still free and cannot damage the car if you choose to fit spacers.

Materials and manufacturing methods

In terms of materials, there are generally two types to choose from: steel and aluminium.

The advantage of steel rims is that they are often cheap, but the disadvantage is that they are easily scratched or otherwise damaged.

Aluminium wheels, or light alloy wheels as they are also known, are a more durable option. The disadvantage of this type of rim is that they are slightly more expensive.

Another factor that affects the properties of a rim is how it is made - a cast rim is cheap but heavy. A forged rim is light but expensive.

Simply put, rims are like many other things: the higher the price, the higher the quality. Forged aluminium rims are therefore generally the best type of rim.

Here at SC Styling, you can buy complete rim packages. This means you get four rims with balanced tyres - all you have to do is fit them to your car on delivery!