ET (Offset): The German Wheel Measurement Standard Explained

ET (Offset): The German Wheel Measurement Standard Explained

Every wheel has an ET number stamped on it — usually something like ET35 or ET45. ET is the German abbreviation for Einpresstiefe, which translates to "insertion depth" — what the rest of the world calls offset.

What ET Measures

ET is the distance in millimeters from the wheel's centerline to the mounting surface (the hub face). A positive ET means the mounting surface is toward the outside of the wheel; a negative ET means it is toward the inside.

• ET45 = the hub mounting surface is 45mm outboard of the wheel centerline (high positive offset, typical of modern FWD cars)
• ET0 = the mounting surface is exactly on the centerline (neutral offset)
• ET-20 = the mounting surface is 20mm inboard of centerline (negative offset, typical of trucks and deep-dish wheels)

Why ET Matters

ET determines where the wheel sits relative to the suspension and fender. Get it wrong and you get:

• Too high an ET: The wheel tucks too far inward. It rubs on the suspension strut, and the tire sits tucked under the fender — ugly and potentially dangerous.
• Too low an ET: The wheel sticks out too far. It rubs on the fender, looks like the wheels are about to fall off, and puts extra load on the wheel bearings.

Changing ET Safely

Going from ET45 to ET35 moves each wheel 10mm outward. That is usually fine — it fills the fender better and clears suspension components. Going from ET45 to ET20 moves it 25mm out, which on most cars will rub the fender.

As a rule of thumb, a 5-10mm change from stock is safe. More than that requires test-fitting.

The Relationship with Width

ET is not a standalone number. A 8-inch wide wheel at ET35 sits in a completely different position than a 9-inch wheel at ET35 — because the extra inch of width splits evenly (half inward, half outward) from the centerline.

When comparing two wheels, you have to account for both width and ET together. The number that actually matters is the distance from the hub face to the outer edge of the wheel — and that changes with both width and offset.

The Stamp

Every wheel has ET stamped on the back, usually alongside the width and diameter (e.g., 18x8 ET45). Always verify the stamped ET when buying used wheels — it is the one spec that determines whether the wheel will actually fit your car.