But I am actually curious about how to model this CoF thing. It is frequently not as constant as it thought to be. So maybe there are some interesting models?
Regarding the tires, it is an interesting question. I would guess, that it should be vice versa. In the limiting case, if you deflate your tires completely, you definitely increase friction force (and CoF as well, since the car weight is the same). So it seems to be counter intuitive to ask to over inflate the tires on snow. My guess would be it is needed to keep the texture of the tire in the optimal shape, since the outside air temperature may be low. This low ambient temperature could drop the pressure inside the tire and deteriorate the performance of the thread. But this is a wild guess. 🙂