[wdfifteen]

Looking from the front of the truck, imagine a circle with its center at the joint at the tie rod end and the rack, with a radius that is the length of the tie rod. As the wheel moves up and down the tie rod end describes an arc on the circle. As it moves through the arc its distance from the center line of the truck changes and the wheel moves in toward the center or out from the center (changes toe) accordingly. Ideally you want the tie rod to be horizontal when the suspension is at its static height.