ET – wheel offset
One of the important standardized dimensions for metal rims and cast wheels is the amount of clearance referred to as ET. The amount of runout indicates how many millimetres the seating plane of the rim is offset from its centre plane. In other words, the ET value influences how much the wheel will be visually recessed inside the body or, conversely, extended outwards.
You’ve probably wondered why the wheels of some cars are almost flush with the wheel arches, while on another car of the same type, the wheels protrude outward from the wheel arches. Or perhaps you’ve just noticed that a vehicle looks much better in the catalog than in reality. Why is that? Where’s the small difference? The answer is simple. In short, the wheels are important for the car, and it’s not just about the size of the rim or the width of the tire, it’s the overall impression of the wheel seating in the body line that is important.
Changing the offset (ET) has a significant impact on how the wheels align with the vehicle’s side lines. If a vehicle has so-called “flush” wheels in the side body line, it usually doesn’t make a good impression. The vehicle appears narrower and less sporty at first glance. Vehicle modifiers and manufacturers are well aware of this, so they adjust the depth of the wheel in the body.
The ET value itself about the wheel’s position in relation to the side line doesn’t say much. You have to compare it with the ET value of the original wheel. When you use wheels with a smaller offset than the original on the same vehicle, the wheels will protrude outward. If the modification is done tastefully, the vehicle will have a more elegant appearance. A similar effect can be achieved with so-called wheel spacers.
It’s essential to realize that this is not just an optical modification; changing the ET actually alters the track width and steering radius. These changes affect several crucial factors, which we’ll mention later. Using wheels with a different ET is, in a way, an undemanding form of tuning. However, keep in mind that in most countries, this is a modification that requires official approval. The correct ET value must match the value in the vehicle’s technical certificate and is checked together with tire dimensions during the technical inspection.
Definition of ET:
ET, or wheel offset from the German term EinpressTiefe, is a standardized value expressed in millimeters. ET represents the distance from the mounting (contact) surface of the wheel’s rim/disc to the center plane of the wheel. If ET is zero, the mounting surface of the rim/disc lies in the center plane of the wheel. Positive ET values move the mounting surface of the rim/disc toward the outer edge of the wheel, while negative ET values move it toward the inner edge of the wheel.
What Can Changing ET Cause?
- Rubbing of tires on the body edges, especially when the vehicle is loaded or when the wheels flex on uneven surfaces
- Rubbing of tires in the wheel arches during turning
- Rubbing of the inner surfaces of rims/discs with the brake components
- Change in steering radius, affecting the force required on the steering wheel
- Change in track width, affecting the driving stability of the vehicle
Where to Find the ET Value?
You can find the size of the ET (wheel offset) of a specific rim/disc on the inner or outer edge. The offset size is a standardized dimension specified by the manufacturer. ET values are indicated on each rim/disc, for example, 6.5J x 16 ET 48.
