ET stands for "einpresstiefe," which translates to "insertion depth" in German. It is a number stamped on the rear spokes or mounting face of an alloy wheel, and it indicates the measurement in millimeters of how far the wheels center line is from its mounting face. The ET value is important because it determines the position of the wheel against the wheel arches. A positive ET value means that the mounting face is toward the front face of the wheel, while a negative ET value means that the mounting face is toward the rear face of the wheel. Zero offset wheels have their mounting face even with the center line of the wheel and are by definition "ET 0". The offset is not the only factor responsible for the location of the wheel against the wheel arches, as the wheel width also plays a role. When planning any ET changes, the standard distance between the wheel and any crucial points of the vehicle should be carefully investigated, including the edges of the wheel arches, brake calipers, MacPherson struts, and other nearby components.