outer edge of the tires. In extreme cases of toe-in or toe-out, feathered edges develop
on the tread across the entire width of the tread face of both radial and bias-ply tires.
Because the objective is to have a zero toe angle under running conditions, most truck
specifications require a zero or a slight toe-in setting. When a fully loaded vehicle is
moving at highway speeds, there is a slight tendency of steering tires to toe-out. Any
looseness in the steering linkage and tie-rod assembly also will contribute to the toe-out
tendency. On newer vehicles, most radial steering tires are set with zero toe angle and
bias-ply tires are set with a fractional toe-in.
1.4.1 Measuring Toe
Toe is specified in either degrees or fractions of inches, depending on the type of
alignment instruments you are using. When a toe-in setting is required, settings of 1/16
inch ± 1/32 inch are usually specified. The toe specification usually depends on whether
radial or bias-ply tires are used. Adjustment of toe angle or dimension requires
lengthening or shortening the tie-rod dimension. This is achieved by loosening the tie-
rod end clamp and then rotating the cross tube.
To determine the cause of excessive tire wear that you suspect to be related to toe
angle, you should first check kingpin inclination, camber, and caster. Correct, if
necessary, in this order. You should not make an adjustment to toe angle until the other
factors of front-wheel align are known to be within specifications.
When measuring toe angle, the front suspension should be neutralized. To neutralize
the suspension, roll the vehicle back and forth about half of a vehicle length. This
relaxes the front suspension and steering linkages. Neutralizing the front suspension is
important before making front-end adjustments, especially if the vehicle has been
jacked up on either side to scribe the tires. This operation causes the front wheels to
angle as each is returned to the floor. When
possible, use a scissor jack that cradles both
sides of the front axle when working on front
ends.
If you begin by neutralizing the front end,
both front wheels should at this point be in
the exact straight-ahead position. Toe-in
measurements should be taken across the
hub centerline, front, and rear on each tire
(
Figure 9-7
. Make sure that the wheels are
on the ground and fully supporting the
vehicle weight. Measure and record the
measurements. The difference between the
front and rear measurements is the toe
specification.
1.4.2 Adjusting Toe Angle
After measuring toe, you can use the
following procedure to adjust toe angle:
Figure 9-7 - Determining toe.
1.
Use the steering wheel to turn the steering gear to the exact mid-position
(overcenter).
2.
Loosen the clamping bolts on both tie-rod ends. Raise the weight off the axles.
NAVEDTRA 14050A
9-8