Wheel spacers needed?

[doonbeg]

...when switching from the standard 19" OEM alloys on my 3.0d Sport to OEM 17" alloys (Style 57)? I have to spend 10 days driving about in Scotland from next week so I'm finally going to have to stick my winter wheels on! (Vred Wintrac Ext 4's). Also, there's a massive difference in the two wheel sets so is it necessary to muck about with the geometry at all?

Btw, in the recent few days worth of icy/snowy weather in Surrey my rear drive 911 on winter tyres was a LOT more effective than the E53 on (admittedly quite worn) Michelin Diamaris..! Goes to show how good the winter rubber is.