I have the stock 17's 225-55-17.

It is not a stag fitment. Should I keep it the same if I go 19 or 20's or should I stag it? I may go for 19's since I daily this car average driving a month is 3500-5000 miles. I also did not want my speedo to be off either =\ any suggestions on tire size and offsets?

2010 G37 Sedan

 

Are you planning on lowering it? If not I'd stay w/ smaller 18s and I prefer a staggered setup, although you're ability to rotate your tires will be limited side to side. If you lower your G then for sure 19 or 20s. Here's my staggered setup. Wheels are 8.5x20 +40 & 10x20 +45, Tires are 245/35/20
295/30/20 speedo is just about dead-on.


Here's a good calculator to play around with
https://www.myg37.com/forums/tire_rim_calculator.php

 

Still debating lowering it or not. Since the g37 anniversary edition comes with 19's it didn't look too bad.