the 18's should clear the calipers, though would still benifit from spacers to fill the arches. No the standard Rays are 8.0 at the front and 8.5 at the back...... dont't know about the standard standard ones though.....
Technically if you kept the tyre sizes the same as stock i.e. different size tyre on the front compared to rears you would still have a wider footprint at the back i think - im sure somebody more knowledgeable can clarify this for you?
I think it's generally accepted that its a better idea to have a wider tyre on the back than the front of a high(ish) powered rwd car, especially on a torquey (sp??!) engine.
I havn't totally ruled out the idea of them yet - just a lot lower down on the priority list now i have spacers for the Rays, and would probs rather spend the money on a plenum spacer & Abbey Re-Map (which will have to wait till i get back from NZ anyway!)
Post some pics up if you do get them though mate - i'm sure they will look great. - if you want to get a rough idea of how they will look try and find a pic of a Z with the Volk TE-37 20Inch models fitted (i think theres a few pics floating around the interweb of an amuse Z with these??)
like this:
https://www.performancenissanparts.com/ ... s/5955.jpg
Jak