Is your ackerman off? When wheels are turned sharp the outer tire should not be turned as sharply as the inside tire. I had this problem on a 66 pu when spindles were changed to disc. brakes. It would wear the outside edges of the tires more than the rest. With a solid axle vehicle an imaginary line should go from center of kingpin thru center of steering arm ( where tie rod ends connect ) and intersect at the center of rear end. If incorrect differnt lenth steering arms or bending of arms (typically out toward tire) would be required.