will these wheel dimensions fit on my Z?

Size:
18x10

Offset:
+30

Backside:
6 5/8

Bolt Pattern:
5x4.5


Also will I run into problems if I keep my front at 17" and go 18" in the rear?
I believe the 06 Z comes that way...

 

You would be fine if those are back wheels.

If that is your front wheels, it might stick out a bit.

If you want to go 17 Front, 18 Rear the car wont complain, the 06 comes 18"/19", I was considering going 275/40R17 Front, 275/40R18 Rear but ended up just going 18s all around.

Chris

 

sorry, yes, it's for the rear, I currently have 17's and want to go to 285 in the rear with the same style wheels and they only come in 18 in fitting the 285's and keep the 17's in the front

 

I did not notice the bolt pattern, is a 5x4.5 the same as a 5x114.3 bolt pattern?

 

I don't know but it's the same that my current wheels have

 

Yes 4.5000 inches equals 114.3000mm.

 

I am finally ordering these...

Is the Backside of 6 5/8 going to be ok?