The more I read the more confusing it becomes. I currently own a 2008 350Z Enthusiast model with stock tire and wheel sizes. Wheel F 18x8 R 18x8.5, Tires F 225/45-18 R 245/45-18. I want to put Bridgestone Potenza RE760 Sport all around. First setup is F 245/45-18, R 275/40-18, Second setup would be F 245/40-18, R 245/45-18. I don't track but drive aggressive. Thanks for the help.

 

There is a sticky with more detailed info, but a short answer is that your first potential setup will not work. You want your rear tire to be slightly taller than your front in order for traction control to not go haywire. In the first setup, your 245/45 fronts will be taller than your 275/40 by a small margin. Not only that, but squeezing 275 width tires on a 8.5" rim is going to be tacky-looking at best, unsafe at most.

Second setup is fine. Square setup (width-wise) will provide more neutral response and helps curb understeer.

 

Personally I wouldn't put 275 on an 8.5" wheel or 245 on 8". In your case, I'd run the stock size combination unless a pair of rear wheels used upfront, then I'd run the 245/40 & 245/45 combination.