wheel spacers on 2004 superb what size do you have?

Hello I have a B5 skoda superb 2004 1.9tdi AWX So seen as nobody really does anything to these cars I thought id wing it and ask

I have standard 17 inch alloys with 225/45/17 tyres on ,

What size wheel spacers do you guys have on your passat?

Ive currently got 20mm on the back and the wheel fills the arch alot better and some how has made the wheels look bigger they looked tiny before.

Although now im worried about the tyres hitting the rear arches when goin over speed bumps etc or havin a full load can this happen ? They look as if theyl just sit inside .

What size should I get on the front should I opt for 15mm or would it be ok to fit 20mm has the arches dont go that far down to the tyre ?

Ive not lowered my car and got told it would look daft with spacers on and not lowered but let me tell ya on the back so far it looks ten times better the wheels now look like they belong on this big car and dont look like 15s in middle of a big arch...