WHEEL ALIGNMENT 2B-3
3. Road test the vehicle. If there is improvement, install
the original tires to find the offending tire. If there is
no a straight improvement, install good tires in place
of all four offending tires.
4. Install original tires one at a time to find the offending
tire.
RADIAL TIRE LEAD/PULL
Lead/pull is the deviation of the vehicle from a straight
path on a level road with no pressure on the steering
wheel. Lead is usually caused by:
lIncorrect alignment.
lUneven brake adjustment.
lTire construction.
The way in which a tire is built can produce lead/pull in
the vehicle.011-center belts on radial tires can cause
the tire to develop a side force while the vehicle rolls
straight down the road. If one side of the tire has even a
little larger diameter than the diameter of the other side,
the tire will tend to roll to one side. Unequal diameters
will cause the tire to develop a side force which can
produce vehicle lead/pull.
The radial lead/pull diagnosis chart should be used to
determine whether the problem originates from an
alignment problem or from the tires. Part of the lead
diagnosis procedure calls for tire rotation that is different
from the proper tire rotation pattern. If a medium- to high-
mileage tire is moved to the other side of the vehicle, be
sure to check for ride roughness. Rear tires will not cause
lead/pull.
WHEEL ALIGNMENT 2B-9
GENERAL DESCRIPTION AND SYSTEM OPERATION
FOUR WHEEL ALIGNMENT
CASTER
Caster is the tilting 91 the uppermost point of the steering
axis either forward or backward from the vertical when
viewed from the side of the vehicle. A backward tilt is
positive, and a forward tilt is negative. Caster influences
directional control of the steering but does not affect
tire wear. Weak springs or overloading a vehicle will affect
caster. One wheel with more positive caster will pull
toward the center of the car. This condition will cause
the car to move or lean toward the side with the least
amount of positive caster. Caster is measured in degrees.
CAMBER
Camber is the tilting of the top of the tire from the vertical
when viewed from the front of the vehicle. When the
tires tilt outward, the camber is positive. When the tires
tilt inward, the camber is negative. The camber angle is
measured in degrees from the vertical. Camber
influences both directional control and tire wear.
If the vehicle has too much positive camber, the outside
shoulder of the tire will wear. If the vehicle has too much
negative camber, the inside shoulder of the tire will wear. The first responsibility of engineering is to design safe
steering and suspension systems. Each component
must be strong enough to withstand and absorb extreme
punishment. Both the steering system and the front and
the rear suspension must function geometrically with
thebody mass.
The steering and the suspension systems require that
the front wheels self-return and that the tire rolling effort
and the road friction be held to a negligible force in order
to allow the customer to direct the vehicle with the least
effort and the most comfort.
A complete wheel alignment check should include
measurements of the rear toe and camber.
Four-wheel alignment assures that all four wheels will
be running in precisely the same direction.
When the vehicle is geometrically aligned, fuel economy
and tire life are at their peak, and steering and
performance are maximized.
TOE
Toe-in is the turning in of the tires, while toe-out is the
turning out of the tires from the geometric centerline or
thrust line. The toe ensures parallel rolling of the wheels.
The toe serves to offset the small deflections of the wheel
support system which occur when the vehicle is rolling
forward. The specified toe angle is the setting which
achieves 0 degrees of toe when the vehicle is moving.
Incorrect toe-in or toe-out will cause tire wear and
reduced fuel economy. As the individual steering and
suspension components wear from vehicle mileage,
additional toe will be needed to compensate for the wear.
Always correct the toe dimension last.
