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Figure 12-6.—Difference of radii between inner and outer wheels. | Up
Construction Mechanic Advanced - Construction methods and practices | Next
Alignment Procedures |
rear of the front wheels, as shown in figure 12-5. Note
that line B is shorter than line A. The setting is taken at
spindle height with the wheels in the straight-ahead
position. Toe-in is measured in fractions of an inch. It is
a tire wearing angle. The purpose of toe is to compensate
for the normal looseness required in the steering linkage
and to balance the effect of camber on the tires. The
natural tendency of the wheel is to rotate like a cone
around the point. If both front wheels are forced to
follow a straight path by the motion of the vehicle, there
is a continual tendency for the tires to slip away from
each other. Toed-in wheels tend to travel toward each
other and counteract this condition. By properly relating
camber and toe-in, tire wear is reduced to a minimum.
The motion of the wheel is balanced between two
opposing forces, and pull on the steering mechanism is
reduced.
Of all the alignment factors, toe-in is the most
critical. A bent tie rod will change the amount of toe.
Toe-in is adjusted last by your turning the tie rod sleeves.
5. TURNING RADIUS. The front-end assembly
of the modern motor vehicle requires careful design and
adjustment because each front wheel is pivoted
separately on a steering knuckle. Because of this
construction, the front wheels are not in the same radius
line (drawn from the center of rotation [fig. 12-6]) when
a vehicle is making a turn. Because each wheel should
beat right angles to its radius line, it is necessary for the
front wheels to assume a toed-out position when
rounding curves. If they do not, the tires slip, which
causes excessive tire wear. The inner wheel (the one
closer to the center of rotation) turns more than the outer
wheel, so it will travel in a smaller radius. This
difference in the turning ratios of the two wheels is
called toe-out. It is usually specified as the number of
degrees over 20 that the inner wheel is turned when the
outer wheel is turned 20 degrees. The-out on turns may
be checked, but there is no provision made for its
adjustment. The steering linkage must be examined
carefully for bent or defective parts if this angle is not
within the manufacturer’s specifications.
6. TRACKING. Tracking (fig. 12-7) is the ability
of the vehicle to maintain a right angle between the
center line of the vehicle and both the front and rear axles
or spindles. (The rear wheels should follow the front
wheels.) If this angle is off, the vehicle will appear to
be going sideways down a straight road. This problem
could be caused by shifted or broken leaf springs or a
bent or broken rear axle mount, bent frame, bent steering
linkage, or misadjusted front-end alignment.
Figure 12-7.—Rear wheels must track correctly.
ADJUSTING WHEEL ALIGNMENT
In the preceding paragraphs, we covered the
principles of the different angles involved in front-end
alignment. In the following paragraphs, we will cover
safety, tools, and alignment procedures.
SAFETY PRECAUTIONS
You should keep the following precautions in mind
when you are working under a vehicle:
1. While repairing or adjusting the steering system
and the wheel alignment, be sure the vehicle is and will
remain stationary. At least one wheel should be blocked
on both sides, even if the equipment is on a level surface.
2. Make yourself familiar with a suspension
system before you work on it; know the “jack” points.
You need to know which components bear the weight of
the vehicle.
3. Make use of jack stands!
4. When using alignment
manufacturer’s instructions.
equipment, follow the
12-5
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