Spacers or not

[pmj]

I am after a set of wheels for my S4 but am not sure about the ET and if I need spacers for at ET of 48 and or 45 can anyone advise me please

[MikeFish]

Depends on the width of the new and old wheels.

If you go to a website like this and put in your original wheel width and offset then the width and offset of the new wheel it will tell you by how much less clearance you will have on the inside or by how much it will stick out.
If you tell us the width and offset of both sets we can help you deicde (sorry I'm not familiar with the OEM offest and widths of an S4 (and you don't even tell us which Shape S4 you have). I'ts basically about getting them to stick out the same as the original ones then adjust it slightly if you prefer them to stick out a little more than standard does etc.

[pmj]

Not sure iOn the standard 18" wheel size for a B8 S4

[MikeFish]

Sorry forgot to include link:
http://www.1010tires.com/Tools/Wheel-Offset-Calculator