I'm considering using 255/40/17 on the front for the track, since I've already got them. The rear I am considering using my existing 18" wheels and most likely using 275/40/18, or 285/30/18. I have Tein Flex and will be able to corner balance this setup beforehand. I also have the base model so no VDC to throw off. Does anyone see a potential problem with this?
I figure that even Nissan staggers 18s and 19s now, so it should work alright. R compounds...

 

The rim diameter is irrelevant. As long as you clear your brakes and you still have room for rubber, anything will work.

It’s the tire diameter that counts for VDC, ABS and such.
Tire width will affect steady state balance in a corner.

 

So different diameters front and rear won't promote understeer or cause some sort of imbalance?

 

I think you should run 275/35/18 if you plan to run 255/40/17 up front. That is, unless you plan to adjust relative ride height (between front and rear) to accommodate the extra tall rear end. Changing ride height between front and rear will affect the car's handling.

 

Ah, good point. I forgot about the roll center being shifted.