I've been watching this thread for several weeks and I've been off reading about tires/wheels at Volvo sites and high performance automobile sites. I have ZERO experience with this concept that 1/2" change in overall radius can effect such dramatically sensible changes in ride quality, cabin noise, and handling. I've seen that car mass, properly tuned suspension, and the many variables of tire/wheel construction and design (depth, thickness, pressure, compounds, width, tread style, mass) all contribute to the feel of the car on the road and cabin. I do NOT get the sense that merely changing from 20s to 19s makes all that much difference unless one takes all the other factors into consideration and can make an informed decision. And I am left with the (perhaps naïve) impression that Volvo is outfitting the C40 with the best tire/wheel for the twin motor version.