All other things being equal (which of course they never are), sedans will usually get better fuel economy than hatchbacks or wagons due to aerodynamics. The larger rear "face" of the hatchback gives a larger wake with resulting higher overall drag. The extra steel and glass hurt some, but the added drag hurts more.
My tires last longer now, at higher pressures, than they used to when I went by the book. They were always worn on the outer edges with deep tread in the middle. Going by the book resulted in classic examples of underinflation. I finally learned my lesson on that.
There's an awful lot of very old information out there re. tire pressures, rooted in the old bias ply tire days, before belted radials.
Please have a look here re. tire pressures.
Driving Under Pressure (full article) - CleanMPG Forums
(photo from the article)
