Anyone advise against 255/45/18 bfg g-force comp 2 -A/S on stock 06 rims? Also will 255/45 look odd with the stock 225/45 in the front? Thank you!

 

Using the "1.2 Factor" (that is, a tire's width should not exceed 1.2x or 120% of the wheel's width) for MAX PERFORMANCE. You can physically mount a tire up to as much as 1.3 or even 1.4x the wheel width but your performance/handling drops off. This works fine for trucks but don't recommend for a Z.

Doing the math..... an 8.5" wheel x 25.4 = 216mm

216mm x 1.2 = 259mm max tread width. Obviously, 255 is right in range.

 

I'm running 255/40 on the rears with 245/40 on the front. What exactly do you mean by look odd?

 

It won't look odd, but you will experience significant understeer with the setup you describe.