Lesson 1/Learning Event 2
Also, the size of the circles that the front wheels travel shows the need
for toeout: The outside wheel is traveling in a larger circle than the
inside wheel. In order to travel in a smaller circle, the inner wheel must
therefore pivot more than the outer wheel. The sharper the turn, the
greater the amount of toeout needed.
The need for the wheels to be toedin in the straightahead position and
then toedout on turns is a difficult design problem. The problem is made
even harder by the fact that when the vehicle is turned to the left, the
left wheel should pivot more, but when turned to the right, the right wheel
should pivot more. Let's take a close took at the steering linkage to see
how this is done.
With the steering arms set at right angles (90) to the wheel spindles, toe
out on turns could not be obtained. Both steering arms would pivot the same
number of degrees when the tie rod moved a given distance lengthwise to the
axle. For example, if the left steering arm and spindle pivot 42, the tie
rod moves the right steering arm the same distance, pivoting it 42. Both
steering arms move the same distance lengthwise to the axle and pivot on
identical segments of an arc.
However, the steering arms are not at right angles to the spindle. If the
tie rod is behind the axle, the steering arms point inward when the wheels
are in the straightahead position. With this arrangement, the wheels will
toeout on turns because the steering arms do not pivot the same amount when
they move the same amount lengthwise to the axle. For instance, if the left
spindle pivots 50 to the left, the right spindle pivots 42. However, both
spindles move the same distance lengthwise to the axle, because the steering
arms are pivoted on different segments of an arc.
Toeout is generally spoken of as the number of degrees over 20 that the
inner wheel is turned when the outer wheel is turned 20. For instance, if
the right wheel is turned 20 and the left wheel 23 on a left turn, the toe
out is 3.