No Math Ackerman Compensation Visualization Kit

Materials required: a sheet of paper, a round lid for making circles, a pen or pencil, and a straight edge such as the edge of a piece of junk mail.

Suppose you are going straight and about to make a right turn. When you turn right, pretend you move along the arc of a circle. The problem is that the right front wheel moves along the arc of a circle that has a smaller radius than does the left front wheel. So if the left wheel stays tangent to the outside arc and if the right wheel is parallel to the left wheel, then the right wheel is not moving tangent to the inside arc and there will be tire scrubbing. Similarly if the right wheel stays tangent to the inside arc of the right wheel, then the left tire scrubs. So you want the right wheel turned a little more than the left wheel so both wheels can stay tangent to their respective arcs. To simplify the discussion, pretend the king pins are vertical. Now pretend you were sitting in your trike and just stood up, so you are standing over the front wheels looking down. Here is a rough sketch of the relevant parts

Now make a sketch, completely out of scale, to visualize why the right wheel turns more than the left when turning right because the lines through the kingpins and tie rod ends point inward:

Using a round lid, draw two nearby circles resting on the edge of your sheet of paper. Arcs along the circles will represent the arcs that the tie rod ends move along.

Now I mark the length of the tie rod along a straight edge (I used an index card) and I move the right hand mark up along the arc on the right hand circle, representing the motion of the right tie rod end, and I keep the other mark on the left hand circle, whose arc represents the motion of the left tie rod end:

Now to see what has happened, I remove the index card, and indicate how each wheel has turned:

The dashed red lines indicate the new directions of the wheels. Of course, the drawing is not to scale and the inclinations of the lines through the kingpins and tie rods are exaggerated in order to see more clearly why the right wheel turned more than the left wheel.