SO2's are 225 (very wide 225's). The 245 is comparable to the SO2 225.
I put 225's (Kumho's) on the rear and the handling was very very crappy. Now I have 245's and the handling is much better, but still not like the SO2's. But I see that you already have 245's, so maybe your tire is a much harder tire than S02's. That makes for a less smooth ride.

 

Yeah, you are right. I had the right idea, but I mixed up the tire sizes. 225 just didn't seem right in my head. I must have been spending too much time in 'vette-land lately.

 

Yeah i talked with Jim before buying the 245's...they're Yoko's, not bad tires by any means...the old tires seemed to have worn evenly, howeverrrrr i had gotten either a broken belt/separating belt before i replaced them and they became undriveable. Allignment i think is a good option, if it doesnt help...then i'll just

 

The more aggressive or euro alignment specs makes the car more nervous feeling at high speeds. It's a handful above 100+, but mid speed cornering is incredible. It's a coin toss, but I sided for more stability. The steering will become quite twitchy with an agressive alignment. I'd definetely have the alignment checked, but if you want high speed stability, keep it to the US alignment specs.

 

improve your own body's balance and reflexes and do not tense-up when you drive at high speeds. the s2000 is a tad light weight but has good aerodynamics and is very stable as long as you keep yourself focused on driving and keep two relaxed hands on the wheel. i have never felt anything like zipping down the freeway at 150 mph on fresh tires and a fresh alignment. the car went everywhere i wanted it to go and no where else.