I wondered the age, because if they are old worn out tires, the sidewall may have more flex and allow your car to be a little squirly. If you get some run-flats like my Kelly Springer tires were, they are stiff and stable as hell. The tire shop had a bit of a time getting them mounted, but eventually got the job done.
Also, my 245's up front followed the lines of the road big time, jerking the steering wheel around. I dropped down to 235's which made the tires less square, and my road tracking problem went away. If your car isnt lowered though, the 235's will look small and give you a huge fender gap.