My stock 17" Serapis will become my winter wheels. Whatever I end up going with will be strictly summer. I found a good deal on a used set of Heicos in 19x8, 235x35/19. I think I may pass on them though, as the 18 would get me the performance/appearance that I'm after without the risk of wrecking tires/rims.The "35" is a ratio and is going to be dependent upon what your width is. I ran a 245/35 18 and it wasn't too bad. Though our roads are very smooth here.
Personally, I think 19" wheels are overkill. They can look great, but they're heavy, they make your brakes look tiny, and you can't run a tire with a sufficient sidewall. Insufficient side wall means a harsher ride, more likely to crack/bend a wheel when you hit a pothole, and a loss in cornering performance. It has been debated that 17" wheels are actually the optimal setup for these cars; you can run tires that will have proper flex through the corners, the ride will be fairly decent, and your overall wheel/tire weight may be less. This is part of why Volvo sold the 250 Polestar Luxury Editions with 17s, even though all their R-design counterparts had 18s.
I've driven a few P1 Volvos with 19s (on springs and coilovers) and the ride was significantly more harsh than my car on 235/40 18s.
I assume you have a separate set of winter wheels in Connecticut? If you're just going for summer show (and don't mind your brakes looking small) 19s aren't bad. But if you're going for a balance of style and performance, stick with 18s.
Maybe you can find a local P1 owner with 19s who would be willing to take you for a ride. Then you can judge for yourself if it will be too jarring for you.
