I can't say anything about your offset since I am not an offset expert. Actually, I am not even a tire/wheel expert. I think you should be fine with 245/40/18 front and 265/40/18 rear for your 8.5" and 9.5" respectively. These your stock 06 rims?

From what I heard, you can add about 20 mm to your tire width for the stock 35th anniversary wheels (aka '06 standard rims). I want to go with 245/45/18 front and 265/45/18 for the rear. Problem is the tire I want for the rear comes in 275/40/18...so I am hestitant getting that tire size for my 9.5" rim.

 

zzz350 i work at a place where i have to get down into a garage so thats why im worried about putting a lowering kit on the z. On my other car i put a bag system on my car to get into the garage but don't feel like doing that to the z.

 

If you can live with the more expensive tires, go with 19". They do look much better.

 

Then you should probably stick to 18"