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      08-01-2010, 01:55 PM   #6
cryptic23
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Drives: bmw x6
Join Date: Jul 2010
Location: UNITED KINGDOM

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Yes of course you do, you can not just put any wheels on a car.

Your car requires a unique offset. This is where the wheel will sit in relation to the bodyline of the vehicle, realistically you can go 5-7mm outside these recommendations, but always consult a technician if you are unsure, as there are often other factors that need to be considered. Offset is usually stamped on the wheel in the X6 case et40 and back et37. This is measured in millimetres of et (et is the short form of the German word 'Einpresstiefe' which literally translates as insertion depth).

Basically the wrong ET and the wheels will not fit properly.A wheels offset is the distance from the centre of the wheel to the face of the bolting plate.Effectively the offset is also the distance from the centreline of the wheel to the hub face.

Therefore :

If you put a wheel on the same hub with a bigger offset, the wheel will sit further inside the wheel arch because the wheels bolting face will have to move further in to meet the hub. Alternatively if it has a smaller offset it will sit further out from the wheel arch.
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