Hey guys need some help deciding on new Rim's for my 06 sti.

I was hoping to get some Rota Grid R's (18"x9.5) just for looks, then swapping back to stock 17" rims for track days. The rota's won't fit with that offset without guard rolling, camber etc. I don't want to do anything like that to my car, but I found a picture with some really nicely fitted Grid R's:





It doesn't look like the owner has rolled the guards or has any camber. the Rims sit nicely in the guard. What I was looking at here are the disks behind the Rim, what are they? where can I buy them? Will this ultimately have an affect on my handling/ performance when I try and put the stock 17" rims back on and use the car on the track? Sorry if I sound like a noob, any help on this would be great, thanks guys.