Well consider this. The stock sidewall is 4.3 inches. 225/45 has a sidewall of 4 inches. 255/40 also has a sidewall of 4 inches.

Bottom line, the kind of tire will play a HUGE part in ride quality. So I submit the biggest factor is the fact you went to the RSA's. As much as people hate RSA's, they actually have pretty dang good ride quality. They also handle decently. Now the grip is horrible, and the reliablity as well. But again, very good ride quality for the type of tire.

Here is my setup...
18 X 8 wheel with +30mm offset. I have PS2 255/40's mounted on them.
My konis are set to max stiffness. The rear AGX's are set to #8 (max stiffness). The tire pressures are 33psi front and 32psi in the rears. Progress rear sway bar with rear end links set to 1 inch spacing. I have progress springs all the way around with the rears raised with a custom spacer by .8 inches to counter the drop of the rear springs plus leveling. The car sits at 26.5 inches in the front & 26.75 inches in the rear at 1/4 tank of gas. With a full tank the rears go down to 26.5 inches.

The car handles like a dream. I constantly whip it into turns and weave it left & right just to feel the car talking to me. The car is ridiculously fun to drive. Because of the total weight of the wheels+tires (48.5 pounds) she is very responsive (plus a slightly lower gear ratio). I can feel each and every corner of the car. The lean is minimal but the ride quality (here is the kicker) is superb. Taught but subtle. Isn't bothered by large potholes and tracks perfectly. You can let go of the wheel and speed over potholes without altering your direction.

Tires are the only thing making contact to the ground-be sure not to compromise this very important aspect of grip, handling, road noise, ride quality, longevity, looks, ability to deal with rain, heat, snow, turn in response, braking, and one of my favorites driver feedback.

There is no question about it, a lighter wheel will outperform a heavier wheel. Period!!!

"Unsprung Weight Transfer is calculated based on the weight of the vehicles components that are not supported by the springs. This includes tires, wheels, brakes, spindles, half the control arm's weight and other components. The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression--which induces a force on the unsprung weight. In time, the unsprung weight then responds to this force with movement of its own. The amount of movement is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip when tracking over an imperfect road. For this reason, lighter wheels are often sought for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality is deteriorated.

Pneumatic or elastic tires help by providing some springing for most of the (otherwise) unsprung mass, but the damping that can be included in the tires is limited by considerations of fuel economy and overheating. The shock absorbers, if any, damp the spring motion also and must be less stiff than would optimally damp the wheel bounce. So the wheels execute some vibrations after each bump before coming to rest.

High unsprung weight also exacerbates wheel control under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control.

 

I noticed the most change in off-the-line acceleration. Its like a lightened flywheel: you notice it more when you rev your engine. It takes less energy to get the mass to rotate with both lightened flywheel, lightened crank pulley, and lighter rims.

 

I agree. I can either do the flat black without the chrome or gunmetal. That will *sort of* offset the small wheel. Honestly, I never really cared about having big rims, but I do understand that puny rims on such a big sedan will hurt the overall appearance. We'll see.

Joshua