The HF toe-in tool looks like it registers off the sidewall of the tire. The problem I see with this is that the sidewall is not necessarily straight and can wobble. The afore mentioned method, that is, marking a line on the axial centerline of the tire, while rotating it the full 360deg is the most accurate method. A scriber was mentioned, that will give a fine line and give you the most accurate reference. A white pencil would work but by the time the tire came round full circle the line would be an eight of an inch wide, not to accurate of a reference point.
As far as the horizontal height of your front to back measurement being affected by the caster angle, a little trig will show you that the measurement could be taken up or down a few inches from the horizontal center line and it would be little affected, at least not enough to be noticed by the resolution of a tape measure.
Back tilt of the kingpin is positive caster angle, forward tilt of the kingpin is negative caster angle, PERIOD! Kingpin inclination and camber are best left to the alignment shop, they are a little more difficult to measure accurately in the garage. You could change the Caster at home but the Camber angle can’t be changed with out cold bending of the axel.
Denny Graham
Sandwich, IL
