Use a tape measure, measure the front and the back of the tire, measure straight up, that should put you basically where you need to be, when I changed mine, measured within a eighth toe out, tires are wearing normally.
"Its a Ford. Nuff said. Everything else is just a glorified tonka toy"
"ASE" Certified" Parts Professional
92 F150 302 4x4 Long bed Extended cab
2001 Taurus wagon