i sold tires for 6 years, Ive seen it all. mileage warranties are only there to get you back in the store when they run out of tread early. all warranties are prorated. (i worked at goodyear) having put them on my sisters and moms cars, (i don't like many good year tires) the goodyear assurance triple treads are one of THE best tires you can put on your car for your family's safety. not a sales pitch haha i hate 90% of goodyear tires, they just payed rent and food bill as far i saw. but the triple treads really make a difference in rain and in the vehicles handling. i first hand took driving tests on road courses with them and saw how they are made. they are top notch. you might spend 100$ more for the set then some other tires, but believe me you dont want to skimp on tires and they destroy those yokohamas (soft rubber! blech). look into them
always get your vehicles alignment checked when you get new tires or soon after, its a quick way to throw money out the window if you dont, and keep them rotated
best tires you can put on your car - heres a link
http://www.tirerack....lay.jsp?type=AS <--- rating
http://www.tirerack....ance TripleTred <--actual tire
Im not trying to be pushy but your comment about it being the grocery getter is the most important comment, those vehicles need the best tires you money can afford on them, they are involved in the most accidents and suffer the most punishment of any vehicle on the road.
nitrogen is really a waste of money, your better of just checking your tire pressure every other week with a 99 cent gauge and getting FREE air in the any way. tires pressure increases with temperature and air loss really isn't that big of an issue now a days, most tires have a haylibutal (cant even spell it) lining the prevents any air escaping from them. Besides, air is 80% nitrogen anyway, you are already using a blend. haha its just not worth the money