I can't say I noticed any difference in ride quality going from 255/50/16 down to 255/40/18.Partially for looks, partially to save on raw materials for the tire companies. Overall, I like the look better than the old tires that had massive sidewalls. There's probably a performance gain to be had too but ride comfort is sacrificed. Like anything, it's a trade off.
So we've been talking about this for a few days now. Have you decided on something yet?
I did notice a marked improvement in cornering response due to less flex.
Long story short, I think the primary reason that more companies are reducing the number of 15 and 16" "performance" tires is lack of demand, especially in such small contact patches as we have with 215 and 225 series tires.
There are enough tires out there for replacement for older cars, especially in a very common passenger car size like 225/60/16, but not many "performance" types in that size. For Muscle Cars, you have the specialty aftermarket repops like Coker, but as we well know, if you want to upgrade the performance on your 1960's or 1970's muscle/pony car, more modern sized (larger diameter, wider series, lower profile) improves cornering, traction, and acceleration dramatically.