What are the widest possible wheels/tires that can be put on the Z?

Tire wise, the highest I've heard of is 295 in the rear.

 

the fattest wheel i've read about was a 11" SSR on the Brembo show car.

pretty sure you can do better

anything can be done with modifying

the veilside car with the v3 kit is running 20" with a negative offset, they are using a 10" rear, but they could have gone with 12s or more.

 

How wide can you go without modifying anything (ie rolling fenders, etc), especially taking into account lowering the car? 18x9? 18x9.5?

 

my track rims will be 10.5 rear on a 18in rim, if that helps

 

It helps if you're lowered and they don't rub

 

sorry,
no rub, wheel-CE28n, offset:+28 lowering in a couple months once i get my coilovers

 

20x10's don't rub either.

 

I think they were running 315's on the rear of that car. Looked awesome

 

Wald's show car.
19x12 in the rear, car is on bags btw.

Better pics do exist, this is all I could find ATM.

 

Is 315 possible as a simple bolt-on without touching anything else?
According to tire calcs, 315/35/18 could work perfect.

 

it depends on the tire brand. Some tires are blocky and others are rounded. that is a pretty damn big tire, most likely you will have rubbing issues.

 

The recomended rim size for a 315mm tire is an 11-12in wide rim. Anything narrower will actually reduce the contact patch of the tire as the outer contact edge will be drawn "under".