Hi everyone. I have an 06 350z coupe with 225/45/18 front and 245/45/18 rear (factory). I have a friend who mounted 255/40's on my front wheels and we installed them on my car with no clearance problems. (the dimentions of those 2 sizes are very very similar. the 255 40's are only slightly larger in diameter) (of course the width is about an inch wider) (thats what i'm after...) --- My question is the rears.... I want to put 275/40's on the rear. Those two tires are virtually identical !! (245/45 and 275/40) once again, the width is greater by apprx. 1 inch... --- Has anyone done this to their Z ???

That is very common with 18's....go ahead! No problem!
front: 255/40/18
rear: 275/40/18