How much difference will I notice in ride comfort between riding on 235/45/17 vs 245/40/18 tires and wheels?

I have some aftermarket 17" wheels that have never fit perfectly even with spacers. They are just too sensitive to any misalignment and almost impossible to keep properly balanced. I am getting ready to buy some OEM 18" Lexus GS430 wheels for my GS400 in order to hopefully eliminate this balancing issue and get a better fit. I am just wondering how much ride comfort I will be giving up for this swap.....to me personally I don't really want to swap ride comfort for cornering ability and looks but I am tired of dealing with my balancing issues with wheels that don't fit properly.

I am hoping that overall I will be better off with the OEM 18's than 17's that don't get the job done.

 

18s with those tires will ride pretty smooth. Probably won't even notice the difference.

 

The difference is negligeble. Tires has more to do with ride quality at those wheel size. You can still have a decent amount of sidewalls with 18s.

 

it will still be very confortable with 18's

 

I have 245/40/18 up front on my other car. Ride quality is ok but you need a tire with good sidewalls if you have potholes and such.