Ackerman illustrated


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Ackerman is the term used to describe steering geometry that causes the inside front wheel to turn "tighter" than the outside front wheel. There are a number of methods to obtain this "effect". The most common method is illustrated below.

As you can see in the illustration, Ackerman is a geometric issue, that is caused by angling the pitman arms toward the center of the kart. It can also be caused by using multiple attachment points for the tie-rods at the steering shaft (explained at the bottom of the document).


In the first example at left, you can see that the pitman arm has no offset at all... (ie: the pitman arm points directly back, and is at 90 degrees to the spindle).

I've rotated the front spindle/wheel assemblies based on 1" of tie-rod movement (magenta), and 2" of tie-rod movement (blue).

Note that in the first example, both wheels turn the same amount (in this case; 36 degrees)

In the second example, I have offset the pitman arms 15 degrees (towards the center of the kart).

Once again, I've shown what happens with 1" and 2" of tie-rod movement. As you can see, the inside front wheel now rotates 42 degrees vs. 34 degrees for the outside front wheel.

Please note that these examples assume you have a single attachment point for the tie-rods at the steering shaft.



These examples are a close approximation of what actually happens. To be 100% accurate, I would need to figure in the small amount of cosine error introduced because of the tie-rods being at a slight angle after the 2" of movement, but the error is negligable.

Ackerman effect increases as the pitman arm inclination angle (towards the center of the kart) is increased. If the pitman arms were perpendicular to the spindle, (ie: pointed straight back), AND both tie-rods were connected to the same point on the steering shaft, there would be no Ackerman effect.


Ackerman can also be caused by having a tie-rod attachment (at the steering shaft) as in the illustration at left. If the tie-rods are each bolted to one hole, (ie: the left tie-rod to the left hole, and the right tie-rod to the right hole), you increase the Ackerman effect. If the tie-rods were to be attached in a manner that would make them cross over each other (ie: one to the front side of such a tab, and the other to the back side, allowing them to "cross over" each other), you would create anti-Ackerman.....in other words, you would offset the Ackerman created by angling the pitman arms as in the illustration above.