It's a small difference but not ideal.

Stock diameter with 215/55 is 26.3, while youth new 225-50 are 25.9" in diameter.

Either way, I would put the correct size tires on. You either want 215/55 or 235/50. If you are using this car year round in snow and only use 1set of wheels, go with the 215/55.

Did you not sake for a specific tire size before you went In for tires? Or did they put something different on?

With wad, you should replace all four at once anyway. On some gm models, the all wheel drive system will go into error if you change only two because it senses the difference between new tires and worn old tires. The g35 system has some slip built in, but do not hit the snow button with two different tire sizes or you can cause some damage then

 

You don't have to run 215/55 or 235/50, you just have to run the same diameter front and rear and be close to the stock diameter of 26.3". Here are the sizes you can run on a 17x7:

215/55-17 (26.3" - stock)
225/50-17 (25.9" - 1.7% smaller than stock)
225/55-17 (26.7" - 1.7% larger than stock)
235/50-17 (26.3" - stock +0 sizing)

They're all close enough to 26.3" so you won't have problems with the VDC, and as long as they're all the same diameter, your AWD won't be affected. Notice I said same diameter. You can run a 215/55-17 up front and do a simulated stagger with a 235/50-17 in the rear without any problems other than you can't rotate them and have to watch your tire wear a little closer. I run 225/55-17's in the winter and don't have any problems

 

oops i meant 225/45 front and rear 245/45