What Is ET?
ET is a common notation for wheel offset, derived from the German word Einpresstiefe, meaning insertion depth. It is usually expressed as ET followed by a number in millimeters, such as ET35 or ET45.
In most wheel listings, ET35 means a +35 mm offset: the wheel’s mounting face is positioned 35 mm toward the wheel’s outer face from the wheel centerline. ET is also known as offset notation.
ET describes wheel position, not the bolt pattern, center bore, wheel diameter, or wheel width.
How ET Offset Is Measured
Wheel offset is the distance between:
- The wheel’s centerline
- The wheel mounting pad that contacts the vehicle hub
The three basic offset positions are:
- Positive offset: The mounting pad is toward the outside face of the wheel. This is commonly written as ET35, meaning +35 mm.
- Zero offset: The mounting pad sits on the wheel centerline, written as ET0.
- Negative offset: The mounting pad is toward the back or inside of the wheel. This may be written as ET-10 or ET−10, meaning −10 mm.
ET values are measured in millimeters. The marking may be stamped or cast on the back of a wheel, near the spokes, or included in a wheel specification such as 18×8 ET45.
Why ET Matters for Wheel Fitment
ET determines how far a wheel sits inward toward the suspension and brakes or outward toward the fender. A change in ET can affect:
- Inner clearance to the brake caliper, strut, and suspension components
- Outer clearance to the fender or bodywork
- Tire position relative to the wheel arch
- Steering and suspension geometry
- Whether the wheel can achieve a Direct Fit on the target vehicle
A lower positive ET generally moves a wheel farther outward, while a higher positive ET moves it farther inward, assuming the wheel width stays the same. However, offset should not be evaluated in isolation. Changing wheel width also changes the wheel’s inner and outer edges, even when the ET number remains unchanged.
For example, moving from ET45 to ET35 on the same-width wheel moves the mounting position and wheel approximately 10 mm outward. That does not guarantee clearance, because brake, suspension, fender, tire, and vehicle-configuration requirements still need to be checked.
ET Compared With Other Wheel Dimensions
ET is only one part of wheel compatibility:
- Bolt pattern / PCD determines whether the wheel’s lug-hole pattern matches the vehicle hub.
- Center bore determines whether the wheel fits over the vehicle’s hub. A larger wheel bore may require hub rings; a smaller bore cannot fit over a larger hub.
- Wheel width changes the total inner and outer position of the rim.
- Wheel diameter affects the tire size and overall wheel-and-tire package.
- Lug hardware and seat type must also match the wheel and vehicle requirements.
Two wheels can have the same ET but different widths, resulting in different clearances. Two wheels can also have the same ET and width but different bolt patterns or center bores, so ET alone does not prove interchangeability.
Common ET Fitment Mistakes
- Treating ET35 as a bolt-pattern specification
- Assuming the same ET fits every vehicle
- Comparing ET values without considering wheel width
- Assuming a spacer changes ET without checking the resulting clearance and hardware requirements
- Ignoring brake clearance, tire size, or fender clearance
- Assuming a wheel with matching ET is a Direct Fit when its center bore, PCD, or lug-seat design is incompatible
When comparing a donor vehicle wheel with a target vehicle, use ET together with the wheel width, bolt pattern, center bore, diameter, hardware, and clearance checks. Depending on the complete specifications, the result may be Direct Fit, Fits With Hub Rings, Fits With Spacer, Adapter Required, Check Fitment, or Not Directly Compatible.