Originally Posted by SMOKEY53

They will require more steering input at low speed, round car parks etc.

Spacers are literally as they sound, donut shaped pieces of alloy that sit between the wheel hub and the wheel itself that space or 'push' the wheel out further. Makes the track of the car wider, people do it mostly for cosmetic reasons to give the car a more aggressive stance but sometimes they're also used to clear big brake kits, or to overcome incorrectly fitting wheels that would otherwise foul on suspension components or brake calipers.

If you scroll up, you'll see the sig pictures that 4.8isX5 has - that's an example of spacers.

If you were going to put 325s on the front, you'd want to space the rears out so that the track width increases similarly front to back. Too much track increase on the front can cause erratic handling, in extreme cases it can cause snap oversteer. Plus it will just look weird.