Haha gutted, could of swapped them over on the way though Hamilton
The offset is stamped into the face of the centre with the size of the rim as well (like this 7JX17H2ET39) so that's with it bolted in to the front. The centre is 9mm thick and were it bolts up to the rim is 8mm so by bolting it in from behind it should give an offset of 22. Having said that your rims could be completely different (thinner,thicker,different backspace ect)