They're very close to the same height, just a little wider.
The 245/45's will be about 0.2 of an inch smaller diameter than 225/50's (less than 1%), sidewall height is almost identical.

 

You're going to notice the imperfections in the highway more as you go faster in any car. Driving the G at around the speed limit it should be pretty smooth and quiet. Bring it up to around 80 and you might notice little bumps that you didn't notice before. This is because the suspension has less time to react to the changes in the roadway at higher speeds.

As far as the suspension being jittery, I don't really think it is. Maybe more than some sedans, but less than many. Its definitely smoother than the Mazdaspeed6 I used to drive, and also smoother than the Maxima SE I had before that.

 

i notice it more when i am going around 80. i guess i ll just get used to it.
i came from a honda accord, so big change.

i'll try 225/50 like the manufacture recommended next tire change, which wont be for a while.

fun car tho =)

 

Did you test drive the vehicle before you bought it? How did it feel then, compared to now?

 

Nothing is wrong with you're car. They just have really tight suspensions. So you do feel alot of road bumps and if you hit a big enough dip it will feel like you are going airborne. I should know as I was driving "sporty" on the highway and hit a few dips. Lets just say its nerve wrecking but the car never lost control.

 

they dont have to be big enough dips. i do feel like im going airbone, but i never lose control.
i m just being paranoid or something. i just gotta get used to the sporty setup.

 

i can't complain about the ride quality on my 08 G35S... i came from 06mustang GT on 20's with bald tires.

 

I lowered mine and put on 19s. Let's just say I feel more of the road, but not that bad.