The 255 will give you more of a "muffin top" look, if that's what you're looking for. More rim protection of course, but if you're trying to get a square sidewall look then it isn't for you.

 

what do you mean by muffin top? i created this post and was thinking of running 235x19 and 255x19. do the smaller tires tend to look like that? does it go away when running a 275? just a bit confused. thx

 

He's referring to a more "pinched" mount so the middle of the tread rides a bit higher. A 9" rim won't be much trouble for a 255, but the main disadvantage for running a pinched mount would be sidewall roll under hard cornering. If it were a 8" rim then it would be a definite no-go but the 255/40/19 has a standard mount range of 8.5 to 10" wide rims so you're in the green
Here's a good tire source for rim/tire fit, scroll down about 2/3rds and you'll see a small calculator titled An ideal rim-width calculator (plus there's plenty of other good info and calculators on those pages).
Car Bibles : The Wheel and Tyre Bible

 

Pinched. That's the word, Brad. Pinched vs. Stretched.

Although I suppose muffintop works. Too funny.

 

My set of wheels dont say "ENEKI"... are they knock offs? is there any way of telling apart?
I just realized this today....

 

Yours is a 2009. I believe Enkei started stamping "Enkei" on the lip in 2010.

 

Does Enkei make all the wheels for every G37? I love those IPL wheels.

 

Rays made some for the earlier G35s but AFAIK Enkei supplies all of them now.

 

If they made IPLs with better offsets, the G35 crowd would be ALL over them and not the OEM Rays

 

yes spacers will def get them pushed out towards the fender...I run 20mm spacers with 245/40-19s all the way around