I'm not sure if this is a null question but I'm wondering if I can upgrade the tires on my stock 18 inch Enkei wheels to a beefier size without damaging the AWD system or the chassis. I was thinking of 245/45/18 which I found is a used size by the other option for the G37xs. I'm not sure to what extreme if any I can upgrade the tire size on all four without experiencing negative effects. I don't think I want to get Goodyears again if that helps any...those All-seasons slip a bit too much for me when its damp out but I do want to keep All-Seasons

As long as the diameter is roughly the same it should not be a problem. I'm running G37 19" staggered setup (245-front / 275-rear) on my Q50s AWD with no problem. The only time you get into issues is when the diameter is way off.