A: Great question! First, new surfaces have more grip because the aggregate in the pavement is more porous and rougher at a minute level. Think of each of those bits of stone in the asphalt, and how the edges on them are rough and even a bit sharp. Over time, with cars sliding over them constantly, those edges become polished smoother and smoother, and the porous empty areas between each stone are filled with rubber. So, with time, the track surface becomes smoother and smoother, and the tire doesn’t dig into it as well.
In my experience, new surfaces do not like old tires necessarily. I think it depends on the type of tire and its rubber compound. When they resurfaced Watkins Glen a few years ago, the grip went up a ton – probably the grippiest track in North America (whereas Laguna Seca is currently the least grippy track). On new race tires, it was amazing how fast you could go, but as the tires ran longer, some of the grip went away. I think it was the porous sharp, aggressive stones in the asphalt ripped up the tires quickly. And maybe – just maybe, because I’m not sure – why an older tire might be better for you on new surfaces – because they’re harder from the heat cycles, the ultimate grip might not be as high, but the grip level they do have lasts longer.