Downsized from 19" to 17" and somehow... ride quality is worse?

Up until about 90kmh in EV mode on a freshly laid road - quiet. Older roads - loud. Even in a prime SE, which doesn't have front laminated glass. I definitely think its the wheel arches. I believe its the same in other priuses too historically, and most hatchbacks as well. When you don't have a full on closed off trunk, road noise in the back will be higher than if you have a closed off trunk.

For priuses in general, I've seen numerous examples of people sound proofing/deadening the wheel arches making a massive difference for road noise in the past. So the gen 5 is likely no exception. I wouldn't mind figuring out a good way to sound deaden the arches in the future, but in a way that doesn't hold moisture thanks to the whole salted roads thing. I've seen so many videos about using specially made foam/sound insulation rather than sound deadening stick on mats for the arches, but if they ever hold salty water from the winter, that's a recipe for disaster. I kinda just live with it. Better than the NVH of my much older 2003 lol You notice it so much even coming from the modern prius on the highway lol

 

Wider and heavier tire & wheel combo almost always cause worse ride quality. No surprise here.
And Prius is a bare bone economy car with no sound deadening to keep the weight down and true to its eco root. Any increase of tire noise will surely stand out more.

 

The brand and type of tire will effect ride quality as much as the size. Also as the tire gets older ride quality will get worse. The CC2 for example are excellent all around tires but aren't known for their ride quality nor are they quiet tires.

If you bought the CC2 for year round performance you got the right tire. But if you wanted something quiet and something that drove a little smoother you got the wrong tire. With tires you can't have your cake and eat it too.