You think I'm gonna rub? Snow tires!
 

So after sliding all around the snow storm on Saturday, I decided to order some Blizzaks. However, they only had run-flats in 245/45/18 for the rears. But I didn't want run-flats, so I found the regular Blizzak LM-25 in 255/45/18.

The reason I ask about rubbing with rear passengers is I have:
RWD S Sedan
Stock 18x8.5 +50
Tanabe NF210 springs
20mm spacers

The fronts I left at 225/50/18, so I'm not worried about that; just the rear.

We do know that a 255/40-19 will fit in the rear w/out rubbing, and it has the same width and overall diameter as the 255/45-18 you purchased. All being stock like we take our fitments from, there should be no rubbing issues.