Wheel offset explained
Offset is the distance in millimetres between the wheel's mounting face and its centreline. It decides where the wheel sits in the arch — further in, or further out.
What ET stands for
ET is short for Einpresstiefe, German for insertion depth, and it is stamped on almost every wheel. ET45 means the mounting face sits 45 mm outboard of the centreline. The number is always in millimetres, even on wheels whose width is in inches.
Positive, zero and negative
| Offset | Mounting face | Wheel sits | Typically |
|---|---|---|---|
| Positive (ET+) | Outboard of centreline | Further into the arch | Most front-wheel-drive cars, ET35–ET55 |
| Zero (ET0) | On the centreline | Centred in the arch | Some off-road and classic fitments |
| Negative (ET−) | Inboard of centreline | Further out, dished look | Deep-dish and heavily modified setups |
Working out the movement
Lowering offset by 10 mm pushes the wheel outward by exactly 10 mm and pulls it 10 mm away from the suspension at the same time. It is a straight one-to-one swap: every millimetre you take off offset is a millimetre gained inside and lost outside.
Changing wheel width complicates this, because the extra width splits either side of the mounting face. Going one inch wider at the same offset adds 12.7 mm to each side. That is why a wider wheel usually needs more offset to stay clear of the strut. The fitment calculator does both sums together.
What actually goes wrong
Too little offset and the tyre catches the arch lip, most often on compression with the steering turned. Too much and the inner shoulder fouls the strut or spring — which is worse, because it can wear through a tyre sidewall without ever being visible from outside.
Offset also changes scrub radius, which alters steering feel and loads the wheel bearings differently. Large changes are not purely cosmetic. Anything beyond about 10 mm from standard is worth checking properly.
Related
How are these fitment figures calculated?
Fitment North calculates declared wheel and tyre geometry from the dimensions shown on the page, using the same tested method as the wheel-offset and tyre-size calculator. Tyre diameter uses rim diameter plus two calculated sidewalls; offset comparisons split width changes across inner and outer edges before applying the offset difference. Results are measurement aids, not vehicle approval. Confirm ratings, clearances and manufacturer guidance before fitting parts.