I'm picking up my new (to me) G37x Coupe tomorrow. I'm planning on using the stock 18" wheels for winter tires, and am trying to figure out what I'm going to do in the spring.

I really like the look of the 19 wheels that come on the Sport model, and I've seen some decent deals on them. The issue is that the default tire sizes are too far apart for my comfort with the AWD system.

Is there any reason I couldn't put 250/40 or 255/40 tires on the rears instead of the 245/45's that come on the sport model? That would put the rears much closer to the diameter of the fronts (225/45).

I've been using this tool to compare widths:
Tire Size Calculator - Discount Tire Direct

I'd still prefer to find same width wheels for all four corners, but am considering my options...

Also, lowering isn't an option due to snow and a very steep dirt/gravel road I need to take occasionally.

 

Haven't been able to find out how much tolerance the car has in it, but I'm going to assume none. Some awd systems barely have 1/32nd tolerance in size from front to rear w/out causing drive train problems. Only two diameters I see that are exact are 225/45-19 and 255/40-19, but not much available in that combo. Personally when in doubt stick with the same size all around.

 

Thanks. I'll just keep to same size wheels when I'm ready for summer tires in the spring.