ET value of a rim: what is it?
The ET value of a rim is the distance in millimetres between the mounting surface of the rim and the centreline of the wheel. This value determines how the wheel is positioned relative to the wheel hub.
The importance of the ET value lies in allowing the wheel to rotate freely with minimal wear, in line with the vehicle’s specifications. Choosing the correct ET value is essential to prevent damage, excessive wear and altered driving behaviour.
Wheel construction and relation to ET value
The determination of the ET value is directly related to the design and construction of the truck wheel. A truck wheel generally consists of two parts:
- the rim (which holds the tyre)
- the disc (which connects the rim to the hub)
The wheel is mounted to the vehicle hub via the disc using wheel nuts or bolts. The position of the disc relative to the wheel hub forms the basis for the ET value. This distance is expressed in millimetres.
Position of the wheel relative to the wheel hub
To determine the ET value of a wheel, we look at a cross-section of the wheel. When the disc is mounted exactly in the centre of the rim, this is referred to as ET0. In that case, there is equal space on both the inner and outer sides of the wheel.
The ET value therefore represents the distance between the wheel hub and the mounting surface of the rim.
Since both vehicle and wheel manufacturers aim to minimise wear, the wheel should be centred as accurately as possible over the hub. It is also important that the wheel can rotate freely without contacting brake discs or other vehicle components.
An incorrect ET value can result in improper load distribution on the wheel hub, leading to increased wear and altered steering behaviour.
Reading the ET value on the inside of the rim
In practice, the ET value is the number in millimetres that indicates how far the centreline of the wheel deviates from the mounting surface on the hub. As a rule of thumb:
- The higher the ET value, the further the wheel sits inward
- The lower the ET value, the further the wheel protrudes outward
The ET value can usually be found on the inside of the rim and is always listed in our product range overview. If you use the same ET value as the wheel you are replacing, you will always be technically correct.
Example: if a wheel has ET35 and you fit a wheel with ET25, the wheel will sit 10 mm further outward. This changes the position relative to the hub, which can lead to increased wear and changes in steering behaviour due to an altered track width.
Frequently asked questions about the ET value of a rim
What is the ET value of a rim?
The ET value is the distance in millimetres between the mounting surface of the rim and the centreline of the wheel. It determines how the wheel is positioned relative to the hub.
Why is the ET value important?
The correct ET value ensures that the wheel is properly centred over the hub. This prevents excessive wear, interference with components and abnormal steering behaviour.
What happens if the ET value is incorrect?
An incorrect ET value can lead to additional load on the hub, increased wear on tyres and suspension components, and a change in track width.
Where can I find the ET value of my rim?
The ET value is usually marked on the inside of the rim and can also be found in product specifications and range overviews.
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