Mo tires, Mo problems

So I picked up two new rears for the rx8 and got them mounted yesterday(decided to go cheap this time, usually run Kumhos exclusively), and threw them on last night. They're a bit wider, went from a 225/45 to a 245/40 on the same 8in wheel. Immediately realized that they wouldn't fit nicely when they rubbed through the first turn. Ran home and pulled the spacers off and went for another spin. Now it under steers a bit harder(expected and I can live) but the real issue is the rear being REALLY floaty and it being very twitchy under decel. Guess I'll be rechecking my rear toe and maybe throwing some more caster on the front tonight. -_-