[JBo]

At 14-16 pounds for street tires you should be underinflated. Never heard of an underinflated tire wearing out in the middle unless the rim width was narrow in relation to the width. jack the rear end up and put tire shine on a foot or two of the tire, slide butcher paper under the tires, lower the car and gently roll the car fore and aft. jack car back up and pull the paper out and "read" it, color or dampness should be uniform across tread. if not, accepted technology says to inflate to put more in center, delate to move to edges of tire. Less inflation allows tires to cup as the side walls expand over the sidewalls. The only kicker here is side wall construction(stiffness) could effect it as well.