I have a 2007 g35x sedan and i just got a set of 15 spoke 19's take offs that come on the '11-'13 sport coupes/Q60 sport. Im currently running the oem 17's with the oem tire sizes (P225-55R17). I also would like to know what size i need for my new 19s. Obviously since i have AWD, the whole set is 19x8.5.

figures you guys can help me out, this is my very first set of tires im going to be buying. THANKS!

 

Check out Toyo's Proxy 4 Plus, I ran them on my coupe all through the snowy NE winter last year and they were OK in the snow considering RWD should be better on your X. They have great tread wear, quiet and handle great through the nicer months.

 

Largest selection will come from 245/40-19. In that size, a very popular option would be Continental's DWS. On a touring based tire, the Pirelli P7AS Plus is the top dog.

 

If it was my car I'd buy winters for the 17" wheels and summer / all season tires for the 19". You could go 225/55R17 or, perhaps better, 215/60R17. There's not as many winter tire choices in 215/60R17 as there in OEM size, but they're narrower for better winter traction and have a slightly taller sidewall for a better ride on crappy winter roads. The 215s are also about 0.4" or 1.5% taller, so a teeny bit more ground clearance and slightly different speedometer error. FWIW, the speedometer in our G35X is optimistic by 3% or more, so a taller tire would actually correct some of that error.

 

Okay, so a quick look at Tire Rack for 19" winters - Blizzak LM32 in 245/40R19 are $268 each, for a total of $1,072. The same tires in 17" are $198 each for the rears (225/55R17) - a total of $792. That's a difference of $280 to put toward 17" wheels.

Not enough? Well, the good news of going to 17" is that you now have choices of other tires. Staying with Blizzaks (so as not to be accused of using low end tires), you can use WS80 tires. At Tire rack these are $132 each (225/55R17) - a total of $528. 215/60R17 are slightly less by $13 a tire, and there are many tire brands and models in these sizes around this price point and even lower cost.

 

^^ DWS ftw. Ran these on my coupe last winter and they handled the snow without any issues, which was super surprising given the RWD. I'd get another set in a heartbeat.
Also that size is perfect for 19s.