Ackerman is the difference in turn radius between
the front tires. On oval track cars it can be
desirable to create a situation where the left front
tire turns faster than the right front tire. The
Ackerman effect can help the car turn better through
the center of the turn. You can measure the amount of
Ackerman you currently have by using a set of turn
plates. Typically, Ackerman is measured by turning the
right front 10 degrees to the left. If you have
Ackerman, the left front will travel further than the
right front. A typical amount would be three degrees
in 10 degrees of steering. To simplify, moving the
right front from zero through 10 degrees of steering
will cause the left front to move say 13 degrees in
Ackerman is created by your front end geometry. Tie
rods that angle forward from the inner pivot point out
to the spindle will have more Ackerman.
You can usually adjust the Ackerman by moving the
left front tie rod end in a slotted spindle arm.
Moving the tie rod end closer to the ball joint will
create more Ackerman. Some cars use an offset slug
design to make the adjustment. Offset wheelbases have
an effect as well. In the shop you should check the
Ackerman on your car at the minimum and maximum
setting. Having this knowledge in your note book will
help you make the quick adjustment at the track.
On 3/8 mile and under tracks more Ackerman is
usually more desirable. On 1/2 mile tracks and above
less is generally needed. Just like with rear stagger,
too much Ackerman will make the car loose on turn exit
or will cause premature tire wear. Too much Ackerman
can over heat the left front so that it will not
perform on the long run. The amount your run depends
on your set up and the track. Some tracks like more
and others less.
Sometimes you can see the effects of excessive
Ackerman by inspecting the wear pattern on the left
front. If you see a graining pattern in the tire
surface or if you have very high pyrometer readings in
the left front you may want to consider reducing the
amount of Ackerman.
Just as with rear stagger the right amount of
Ackerman will help you through the middle of the turn.
Too much and you will not be good on the long run.
Through trial and error you can fine tune the car with
Ackerman. If your car is just a bit tight in the
center then more Ackerman may be the cure. Try adding
small amounts as anything beyond what you need will
just tear up the left front. Too much can also slow
the car down as your horsepower has to over come the
the dragging of the left front through the turn. The
dragging condition will also be very hard on the
performance of the left front tire.
On small tracks Ackerman can be added in aggressive
amounts to see if there is a gain to be had. On large
tracks a finer adjustment should be utilized. Remember
that Ackerman will have the most effect on the car at
the apex of the turn. At the apex, the steering is
turned to the maximum amount for that turn. While
Ackerman has an effect whenever the wheels are turned
the effect is going to be most dramatic at the apex.
There are times when the car will cut to the center
better on turn entry due to the effects of Ackerman.
In this condition, chassis set ups or track layouts
load the left front tire more helping the car get to
the center. While the turn in benefit helps, it may
cause a loose condition on exit due to the steering
being overturned at that point in the corner. A
balance must be found. You may find that you notice
the Ackerman effect on higher banked tracks due to the
loading of the left front where as on flat tracks the
left front has less weight on it causing more of a
undesirable dragging condition.