I have an STOCK 05' GT, and am considering this setup. 20" x 8.5 wheel with a 38mm offset with Falken 245/40's. Will this work?

I'm told that this is the correct offset, but I'm not sure. Will they bolt on and drive w/ no problems?

 

I believe that that wheel and tire combo will fit just fine. But why not get some wider tires like 255's or 275's? When finding what tires will fit wheels you can divide the tire by the wheel width (8.5). Anything between 28 and 33 should be fine. That gives you the amount of millimeters per inch of wheel width.