I have 18"s on the rear on my SRT-6, and I HATE them. I can feel the added wobble in the taller sidewalls when cornering. It's awful. Sure, I get a little bit gentler ride in the back, but that feeling that the car is on rails through a corner is gone.

I'm going back to 19"s before the spring Dragon.

And just in case you're curious, I also have a set of 16"s for the rear for drag racing. They wobble like rubber hose in a wind storm. But they do fit over the rear brakes.