It's hard to quantify as everybody's "harsh or firm " is different. I will say that I much prefer the ride with my winter set up. (16" stock rims/Michelin Alpins) over my summer set ,(17" Racing Harts/Sumitomo HTRZ III's). If I could do it over ,I'd stay with 16' wheels and a bit taller tires for summer. It's a noticeably more comfortable ride and probably not much handling trade off. Also , I'm in the northeast, so the winters really tear up the roads and they are slow to be repaired.
