TÀI LIỆU OTO BẰNG TIẾNG ANH VỀ ECS and wheel aligment_HMC

WHEEL ALIGNMENT & ECS

WHEEL ALIGNMENT
& ECS

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WHEEL ALIGNMENT & ECS

CONTENTS
WHEEL ALIGNMENT

NECESSITY OF WHEEL ALIGNMENT --------------------------------------------------------WHAT HAPPENS DURING AN ALIGNMENT ------------------------------------------------EQUIPMENT REQUIREMENTS -----------------------------------------------------------------HEIGHT MUST BE RIGHT ------------------------------------------------------------------------DIAGNOSIS PROCEDURE FOR ALIGNMENT ---------------------------------------------CAMBER -----------------------------------------------------------------------------------------------CASTER ------------------------------------------------------------------------------------------------TOE ------------------------------------------------------------------------------------------------------STEERING AXIS INCLINATION (SAI) ---------------------------------------------------------INCLUDED ANGLE ---------------------------------------------------------------------------------STEERING OFFSET --------------------------------------------------------------------------------SET BACK ---------------------------------------------------------------------------------------------THRUST ANGLE -------------------------------------------------------------------------------------STEERING CENTER --------------------------------------------------------------------------------TOE OUT ON TURNS -------------------------------------------------------------------------------DIAGNOSIS BY VEHICLE SYMPTOM ---------------------------------------------------------INTEGRATED FRAME AND BODY (MONOCOQUE) --------------------------------------SUSPENSION SYSTEMS --------------------------------------------------------------------------FRONT SUSPENSION ------------------------------------------------------------------------------REAR SUSPENSION --------------------------------------------------------------------------------SPRUNG WEIGHT AND UNSPRUNG WEIGHT ---------------------------------------------SIMPLIFIED SUSPENSION MODEL ------------------------------------------------------------OSCILLATION OF SPRUNG WEIGHT -----------------------------------------------------------

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WHEEL ALIGNMENT & ECS

SEMI-ACTIVE ECS
SEMI-ACTIVE ECS (Electronic Controlled Suspension) ---------------------------------SKY HOOK SYSTEM ---------------------------------------------------------------------------------SKY HOOK DAMPER - ADVANTAGE OF REVERSE TYPE DAMPER ----------------SYSTEM PERFORMANCE -------------------------------------------------------------------------CONSTRUCTION AND OPERATION OF SHOCK ABSORBER -------------------------ECS SHOCK ABSORBER --------------------------------------------------------------------------DAMPING FORCE CHARACTERISTICS -------------------------------------------------------SEMI-ACTIVE CONTROL ---------------------------------------------------------------------------CONSTRUCTION OF SEMI-ACTIVE ECS -----------------------------------------------------INPUTS & OUTPUTS ---------------------------------------------------------------------------------INPUTS
1) ALTERNATOR 'L' TERMINAL ---------------------------------------------------------------2) BRAKE SWITCH --------------------------------------------------------------------------------3) ECS MODE SWITCH (SPORT/NORMAL SWITCH) -----------------------------------4) VEHICLE SPEED SENSOR ------------------------------------------------------------------5) STEERING SENSOR ---------------------------------------------------------------------------6) THROTTLE POSITION SENSOR -----------------------------------------------------------7) ACCELERATION SENSOR (G-SENSOR) --------------------------------------------------OUTPUTS
1) ACTUATOR RELAY ----------------------------------------------------------------------------2) ECS LAMP ----------------------------------------------------------------------------------------3) SOLENOID VALVE (PROPORTIONAL TYPE) -------------------------------------------DTC LIST -----------------------------------------------------------------------------------------------DIAGNOSTIC TROUBLE CODE -----------------------------------------------------------------WIRING DIAGRAM -----------------------------------------------------------------------------------

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WHEEL ALIGNMENT & ECS

WHEEL ALIGNMENT

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WHEEL ALIGNMENT & ECS

NECESSITY OF WHEEL ALIGNMENT
Wheel alignment is just adjusting the relationship between the suspension and steering
components, the wheels, and the frame of the vehicle. Vehicle manufacturers determine which
angles are adjustable from the factory based on need and feasibility. Various adjustment
mechanisms such as shims, cams, threaded rods and slotted frames usually provide enough
adjustment, providing height is correct, to bring the vehicle into specification. When the angles are
all as specified, the car or truck is properly aligned, and the best possible compromise has been
achieved among minimum rolling friction, maximum tire mileage, stability of the car on the road,
and steering control for the driver. Vehicle accident, road shock and general wear and tear can
make some of these angles out of spec. When that happens, control of the vehicle may be
threatened, and the tires may begin to wear unevenly and rapidly. The car needs to be realigned to
have all the proper angles restored.
The warning signs suggesting the need for alignment are:
-

Irregular wear on tires. Look closely at all four of your tires. If one or more of them

demonstrate excessive wear on one side, or wear in a cupped, scalloped or diagonal stripe
pattern at edges or across the tread, or uneven wear but with "feathered" edges on the
treads, an alignment could be needed.

-

Unusual steering feeling. If the steering feels stiffer than it used to, or if the wheel does not
return to the center position when released, or if the car feels skittish the wheels may be out
of alignment.
If the steering wheel pulls to one side when the front wheels are pointing straight ahead, an
alignment is almost certainly needed.
While driving, if the car wants to pull to one side, tends to wander or weave, or is subject to
front end "shimmy", you should have the alignment checked immediately.
There are three basic wheel angles such as Camber, Caster and Toe which determine
whether a vehicle is properly aligned and goes where it is pointed. These three angles must
be set properly for the alignment to be correct.
Four-wheel alignment is essential on vehicles with front wheel drive (FWD) and independent
rear suspension. The rear wheels should follow the fronts in a parallel path. If the rear wheels
are pointed in a slightly different direction, they affect tire wear and the vehicle's stability.

-

-

Common alignment errors to avoid are:
-

Failing to perform an accurate vehicle inspection, including height measurement, to assure
a quality alignment.

-

Failing to pull the rear turn-plate pins during a thrust alignment.
Overtorquing rear hub attachment bolts, causing possible full or partial contact shim
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WHEEL ALIGNMENT & ECS

-

deformation.
Remembering to inspect the vehicle for the presence of a rear shim prior to cutting a new
one.

Other facts should be known about wheel alignments:
-

A wheel alignment should always start and end with a test drive.

-

The front end and steering linkage should be checked for wear before performing an
alignment.

-

The tires should all be in good shape with even wear patterns.

-

Pulling problems are not always related to wheel alignment, problems with tires, brakes and
power steering can also be responsible. It is up to a good wheel alignment technician to
determine the cause.

WHAT HAPPENS DURING AN ALIGNMENT
Before a wheel alignment, a thorough inspection of the entire undercar, including suspension parts,
bushings, steering linkage, ball joints and wheel bearings, wheels and tires as well as the vehicle's
frame and ride height. Loosened or bent parts need to be checked. Once this inspection is
complete, the car will be checked and adjusted on the alignment machine in order, camber, caster
and toe, beginning with the rear wheels.
Items to be checked before the measurement of wheel alignment are :
-

Tire inflation pressure (under standard condition)

-

Uneven wear of tires or difference in tire sizes

-

Ball joint play due to wear

-

Tie rod end play due to wear

-

Front wheel bearing play due to wear

-

Lengths of left and right strut bars

-

Deformation or wear of steering linkage parts

-

Deformation or wear of parts related to front suspension

-

Chassis-to-ground clearance

Alignment checks are recommended whenever steering, suspension parts, or some front-wheel
drive (FWD) driveline components are replaced, or when new tires are installed, or when
customers complain of vehicle pulling or abnormal tire wear such as scuffing, cupping or more
accelerated wear on one side of the tire.
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WHEEL ALIGNMENT & ECS

The type of alignment performed usually is conditional upon the amount of adjustment that's
feasible on a particular vehicle, as well as the shop's equipment capability. On solid-axle, rearwheel-drive (RWD) vehicles, for example, a thrust alignment is usually performed so the front
wheels are aligned to the rear axle. The drive direction of the rear axle is referred to as the thrust
line, which should in theory be the same as the geometric center of the vehicle.

Thrust line
Geometric
center line

A four-wheel alignment involves adjusting the rear wheels to achieve proper camber and toe and a
thrust angle as close to zero as possible, then adjusting the front wheels to the same vehicle
centerline. Four-wheel alignments are recommended for most FWD cars, MPV(Multi Purpose
Vehicles), some SUV(Sport Utility Vehicles) and RWD vehicles with independent suspension.

EQUIPMENT REQUIREMENTS
To perform a four-wheel alignment, a four-sensor machine is required. Turnplates or rear slip
plates at all four corners are needed during both four-wheel and thrust alignments. The rear
wheels must be allowed to relax to their normal position to achieve proper readings whether they
are to be adjusted or not.
In addition to providing caster, camber and toe readings, alignment machines can be used as a
diagnostic tool. Diagnostic angles such as Steering Axis Inclination (SAI), Included Angle (IA),
Setback and Turning Radius can help the technician to identify problems that otherwise might be
overlooked. When the SAI reading is combined with the camber reading, the sum of the two
angles equals the IA. Using SAI/IA and camber will help identify a bent or shifted component. The
optimum setting on all vehicles for Setback is zero, so either a positive or negative Setback
reading indicates cradle shifting or some other component has moved.
Turning Radius, also referred to as toe-out on turns, is determined by the steering arms relative to
the lower steering pivot. When the vehicle is steered into a turn, the steering arms cause the
wheels to turn at different angles, creating a toe-out condition. If the turning radius is incorrect,
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WHEEL ALIGNMENT & ECS
inspect the steering arm and lower steering pivot components for damage. Using the turnplates on
alignment equipment, a technician can check for a bent steering arm by measuring the amount of
toe-out on turns for each wheel and compare them.

HEIGHT MUST BE RIGHT
Some of today's alignment equipment also can diagnose ride height, which is critical to proper
alignment and suspension geometry. Ride height is the angle that all wheel alignment angles are
built around and should be kept within manufacturer specifications for optimum performance of the
entire steering, suspension and driveline system.
When vehicles have been modified from the manufacturer's original design, factory alignment
settings may no longer apply. Altering tire sizes may upset the spindle's distance from the ground,
which can have an effect on scrub radius. Raising or lowering vehicle height may alter the
suspension and steering systems' geometry during deflection and cause excessive toe change or
stress some parts beyond their limits.
Weak, sagging springs can force the entire steering and
suspension system to go out of proper alignment, which spells
problems for any vehicle. A correct alignment with a sagged
suspension can still produce tire wear and handling problems
during dynamic operation. The best way to fix the ride height is
to replace the springs (Note: springs should only be replaced
in matched pairs). Changes in riding height will affect camber
and toe so if springs are replaced or torsion bars are adjusted,
then the wheel alignment must be checked to avoid the
possibility of tire wear. It is important to note that the only
symptom of weak coil springs is a sag in the riding height. If

the riding height is good, then the springs are good.

[Camber change by
a sagging spring]

Air suspended vehicles may have a specified procedure that is necessary to achieve the correct
alignment height prior to adjustment. On some air suspension systems, it is first necessary to
allow the air in the air spring to reach shop temperature prior to alignment.
Failure to detect incorrect chassis height can often lead a technician to a wrong diagnosis, such
as attributing the lack of adjustment range to a bent frame.

DIAGNOSIS PROCEDURE FOR ALIGNMENT

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WHEEL ALIGNMENT & ECS
Tire, brake and driveline problems are often mistaken for an alignment problem by the vehicle
owner, so the customer should be consulted as to what made them think the vehicle needs
aligning. Begin by asking the customer a few simple questions, such as: What is your vehicle
doing to make you think you need an alignment? Does it pull? When does it pull? Is the steering
wheel straight? Are the tires worn unevenly?
Next, verify the problem with a test drive and a complete inspection of the tires and the wear
patterns they display that indicate a steering or suspension problem. If the customer is getting new
tires, examine the old ones for unusual wear before they come off the vehicle. Explain to the
customer how new tires will experience the same wear as the old ones unless the underlying
cause of the problem is corrected.
If a loose steering or suspension part is discovered, show the customer the actual problem. If

possible, demonstrate a properly functioning part on a similar vehicle in the shop for comparison.
Due to the hectic schedule in most shops, this step is sometimes overlooked even though people
learn best from hands-on experience.
It's essential to always be precise when discussing factory specifications for steering and
suspension components. Some chassis parts must exceed a listed tolerance for looseness to
actually require replacement. In many cases, the part can be within its tolerance range but still
contribute to tire wear, alignment and handling problems. Some amount of looseness within this
spec could create problems for the driver of the vehicle, but the replacement is not required until
the tolerance is reached. When making a service suggestion to the customer, explain that
although the ball joint may be within its listed tolerance, the looseness could allow wheel
movement and create alignment angle changes. A part that is loose, but still within its listed
tolerance, should never be described as bad.
Some steering components such as tie rod ends may not have a listed tolerance. Inspection of
these components may rely entirely on the technician's judgment, using hand pressure or some
other approved method as a measure of excessive looseness.

CAMBER
Camber is the angle of the wheel, measured in degrees, when
viewed from the front of the vehicle. The front wheels of the
car are installed with their tops tilted outward or inward. This is
called camber and is measured in degrees of tilt from the
vertical. When the top of a wheel is tilted outward, it is called
positive camber. Conversely, inward inclination is called
negative camber.

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[Camber]

WHEEL ALIGNMENT & ECS
On many vehicles, camber changes with different road
speeds. This is because aerodynamic forces cause a change
in riding height from the height of a vehicle at rest. Because of
this, riding height should be checked and problems corrected
before setting camber. For many years the trend has been to
set the camber from zero to slightly positive to offset vehicle
loading, however the current trend is to slightly negative
settings to increase vehicle stability and improve handling.
If the camber is out of adjustment, it will cause tire wear on
one side of the tire's tread. If the camber is too far negative, for
instance, then the tire will wear on the inside of the tread. On
many front-wheel-drive vehicles, camber is not adjustable. If
the camber is out on these cars, it indicates that something is
worn or bent, possibly from an accident and must be repaired
or replaced.

[Camber wear pattern]

Positive Camber

Vehicle load

Slight positive camber results in a dynamic loading that allows
the tire to run relatively flat against the road surface. Positive
camber also directs the weight and shock load of the vehicle
on the larger inner wheel bearing and inboard portion of the
spindle rather than the outboard bearing. Positive camber in

moderation results in longer bearing life, less likely sudden
load failure, and as a side benefit, easier steering. Excessive
positive camber wears the outside of the tire and can cause
wear to suspension parts such as wheel bearings and
spindles.
Giving the wheel positive camber causes the load to be
applied to the inner side of the spindle, reducing the force
acting on the spindle and the steering knuckle.
The reactive force, which is equal in size to the vehicle load, is
applied to the wheel perpendicularly to the road. this is divided
into perpendicular force to the axis of the spindle and parallel
force to the axis of the spindle which forces the wheel inward,
helping to prevent the wheel from slipping off the spindle. The
inner wheel bearing is made larger than the outer one in order
to bear this load.

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Inner
wheel
bearing

[Vehicle load & Wheel bearing]
Vehicle load

Outer
wheel
bearing

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[Vehicle load & Wheel bearing]


WHEEL ALIGNMENT & ECS

Negative Camber
Variations in negative camber can be used to improve the
handling of a vehicle. A setting of 1/2° negative on both sides
will improve cornering without affecting tire life greatly. This
negative setting compensates for the slight positive camber
change of the outside tire due to vehicle roll, thereby allowing a
flatter tire contact patch during cornering. Excessive negative
camber wears the inside of the tire and similar to positive
camber, it can cause wear and stress on suspension parts.

Rear Camber
Rear camber is not adjustable on most rear wheel drive vehicles. These vehicles are built with zero
camber setting and are strong enough not to flex or bend under normal load. Most front wheel drive
vehicles have a manufacturers specification calling for a slight amount of rear camber, usually a
small amount of negative camber for cornering stability. If the manufacturers specification allows, a
setting of 0° to -0.5°(30’) is preferred for tire wear and ride stability. If rear camber settings change,
defected rear suspension parts are necessarily replaced. However, most vehicles can be adjusted
by using an aftermarket type of adjustment, such as shims, cam bolts or bushings.

Road Crown and Camber
A crowned road means that the outside/right hand side of the lane is lower than the left side of the
lane. This improves the drainage of the road but adversely affects vehicle handling. Road crown
must be compensated for in alignment settings because a vehicle driving on a crowned road leans
to the right, causing some weight transfer to the right, and the camber changes slightly more

positive. This combination creates a pull or drift to the right. Most alignment technicians adjust the
vehicle with a slightly more positive camber, usually 1/4°(15’), on the left to compensate for the
road crown. This slightly more positive camber will not cause a noticeable pull when driving on a
flat road. However, if camber is unequal from side to side with a difference greater than 1/2°(30’),
the vehicle will pull to the side with the most positive camber. If the specifications allow, 0° to
±0.5°(30’) is usually best for tire life and vehicle handling.

Causes of Camber Changes
- Ride height
Always check a ride height specification prior to
beginning alignment. Changes in ride height from
specifications affect camber.

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Pulling to
the right
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[Misaligned Camber]


WHEEL ALIGNMENT & ECS
- Sagging of spring
As a vehicle ages, the suspension has a tendency
to sag. Excessive vehicle weight or abuse can
cause springs to weaken.
- Sagging of cross-member or sub-frame
Another factor to consider is sagging of crossmember or sub-frame. Modifications to the vehicle
such as raising or lowering the suspension or

changing the total weight of the vehicle can also
affect camber.

Problems Caused by Incorrect Camber
-

Vehicle pulls to one side

-

Rapid wear on inside or outside of tire tread

-

Increased wear on the wheel bearings.

-

Increased wear on ball joints (incorrect camber creates
increased leverage on spindle and spindle support
resulting in increased loads on ball joints).

CASTER
Caster can be defined as the forward or rearward tilt of the steering knuckle pivot points, is also
called the steering axis. Caster is measured in degrees, from the steering axis to true vertical, as
viewed from the side. On strut equipped vehicles, the line extends through the lower ball joint to the
center of the upper strut mount.
The caster angle is formed by the steering axis and a true vertical line passing through the spindle.
The purpose of caster angle is to provide directional control stability for the front wheels to travel a
straight course with minimal effort. Proper caster angle also helps to return the front wheels to a

straight ahead position after a turn. Caster has little affect on tire wear.
Purpose of Caster are :
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WHEEL ALIGNMENT & ECS
-

To aid in the directional control of the vehicle by helping the front wheels maintain a straight
ahead position

-

To help return the front wheels to straight ahead position after a turn.

-

To offset the effects of road crown on vehicle direction.

-

To operate in concert with the vehicle suspension design, camber angle and steering axis
inclination angle to provide the desired camber change during vehicle turns.

Many front-wheel-drive vehicles, caster is not adjustable. If the caster is out spec, it indicates that
something is worn or bent, possibly from an accident, and must be repaired or replaced.

Positive caster

Positive caster is when the top of the steering axis it tilted
rearward. The caster line intersects the ground ahead of the
contact patch of the tire, which provides good directional control.
However, excessive positive caster can cause two problems.

The first is that excessive caster will cause a high level of road
shock to be transmitted to the driver when the vehicle hits a
bump and it causes hard steering.

Forward

The second problem is that a tire with positive caster has a
tendency to toe inward when the vehicle is being driven. If one
side has more positive caster than the other, this causes it to
toe inward with more force than the other side. This will cause
a lead or pull to the side with least amount of positive caster.

[Positive Caster]

Negative caster
Negative caster is when the top of the steering axis
is tilted forward. This places the point contact ahead of
the point of load, which provides easier steering at
slower speeds.
However, it can cause difficulty in returning out of a

turn and wandering & weaving at high speeds and
is affected by any road surface variation such as
small road irregularities or bumps. If the caster is
too negative, the steering will be light and the

vehicle will wander and be difficult to keep in a
straight line.
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Forward

[Negative Caster]
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WHEEL ALIGNMENT & ECS

Zero caster
Zero caster is when the top of the steering axis is
exactly vertical. If the vehicle has unequal caster,
the vehicle pulls to the side with the least positive caster.

A maximum side to side variation of ± 0.5°(30’) is
recommended on most vehicles.

Forward

[Positive Caster]
Movement of spindle while turning
With positive caster, the spindle of inner wheel
moves down and the spindle of outer wheel moves
up while turning.
However, it causes the spindle to rise and fall as
the wheels are turned in one direction or the other.
Because the tire cannot be forced into the ground

as the spindle travels in an arc, the tire/wheel
assembly raises the suspension.
That is why steering effort increases when the
positive caster goes up.

[Spindle movement while turning]

TOE
The toe measurement is the difference in the distance between the front of the tires and the back of
the tires. Toe-in, or positive toe, is defined as the front of the tires being closer together than the
rear of the tires. Toe-out, or negative toe, is when the rear of the tires are closer together than the
front of the tires. Zero toe is when the tires are parallel to each other.
Since most alignment specifications show toe as
total toe of both wheels, it is important to
understand that 1/2 of the total toe should be
applied to each front wheel. A minus (-) indicates a
toe-out and toe-in is shown as a positive (+).
Toe-in : B > A, Toe-out : B < A
It is important to note that although toe has
historically been measured as a distance in

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[Toe & Toe angle]


WHEEL ALIGNMENT & ECS
milliliters or decimal inches (B-A), it is becoming

more common to express toe in degrees (α,β). The
idea is that the angle, rather than an arbitrary
distance, determines the side slip of the tire. This
should not be affected by the tire size, but rather
should be constant for a given measurement.
Ex) Toe-in (B-A) mm(in.) : 0±2mm (0±0.08 in.) or 0.09° ± 0.09° (each of α,β)

Role of Toe angle
The main function of toe angle is to cancel out the camber thrust generated when camber is
applied. When the front wheels are given positive camber, they tilt outward at the top. This causes
them to attempt to roll outward as the car moves forward, and therefore to side-slip. This subjects
the tires to wear. Therefore, toe-in is provided for the front wheels to prevent this by canceling
outward rolling due to camber. Since camber approaches zero in most recent vehicles, the toe
angle value is also becoming smaller.
Suspension rigidity and Toe angle
During driving, forces from various direction are brought to bear on the suspension, with the result
that the wheels tend to toe out. In order to prevent this, some vehicles are given a slight toe-in even
when the camber is zero.

Effects of Toe
Excessive toe increases tire scuffing and results in tire wear and drag on the vehicle. Excessive
toe-in, or positive toe, increases scuffing on the outside of the tire. Excessive toe-out, or negative
toe, increases scuffing on the inside of the tire, and in some cases can cause a darting or
wandering problem.
Early indication of toe tire wear can appear as a feather edge
or scuff on the edge of the tire tread surface. Toe tire wear can
also be found on rear tires as a cupping, feather edge or
smooth edge on the tire tread surface. Too much toe in will
cause the feather edge to point in while toe out will cause the
feather edge to point out. Toe is adjusted by turning the tie rod

turnbuckles.

[Toe wear pattern]

Variation from factory specs is usually caused by worn or bent suspension parts or changes in
caster, camber settings. Toe angle can also be affected by body structure or frame damage.

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WHEEL ALIGNMENT & ECS
Toe adjustment
a. Front Toe adjustment
To adjust front toe-in, change the lengths of the tie rod connecting the steering knuckle.
-

Increasing the tie rod length : increases toe-in.
Increasing
rod length
increases
out.

the tie
:
toe-

[Increase of Toe-in]

[Decrease of Toe-in]

b. Rear Toe adjustment
Rear wheel alignment of an independent rear
suspension is accomplished by adjusting the camber
and toe angle. The method of adjusting the camber
and toe angle differs depending on the type of
suspension. Some models have no mechanism for
adjusting the camber.
By turning the eccentric cam, the arm can be moved to
the left or right to change the direction of the wheel,
thus adjusting the toe-in.
As with front toe-in, if the length of the rear arms are
not made the same in order to adjust the toe-in of the
rear wheels separately, the angles of the left and right
wheels will differ no matter how correct the toe-in is.
For this reason, first of all, correct the angles of the left
and right wheels, then adjust the toe-in.

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[Correct adjustment]

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WHEEL ALIGNMENT & ECS

STEERING AXIS INCLINATION (SAI)
The axis around which the wheel rotates as it turns to the right

or left, is called the steering axis. Steering Axis is an imaginary
line through the upper and lower ball joints (pivot joints) on
short & long arm suspensions (ex. Double Wishbone type
suspension). This axis is found by drawing an imaginary line
between the top of the shock absorber’s upper support
bearing and the lower suspension arm ball joint (in the case of
strut type suspensions).

SAI

Steering Axis Inclination (SAI) is the angle between the
centerline of the steering axis and vertical line from center
contact area of the tire (as viewed from the front). SAI is also
referred to as KPI (King Pin Inclination) on trucks and old cars
with king pins instead of ball joints.
Steering offset, or Kingpin offset is the distance between the
wheel center and the point at which the steering axis intersects
the road surface. It is negative when the point of intersection is
between the center and the outside of the wheel.

Steering offset
[SAI of MacPherson Strut
type suspension]

SAI provides good driving and handling characteristics through
directional stability and weight projection. Directional Stability
is the tendency of a wheel to straighten from a turned position
and remain straight.

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Center
[SAI of Service
DoubleTraining
Wishbone

type suspension]


WHEEL ALIGNMENT & ECS
Since the wheel turns to the right and left with the steering axis
as its center and the offset as the radius, a large offset will
generate a great moment around the steering axis due to the
rolling resistance of the tire, thus increasing steering effort.
If the offset is too large, the reactive forces acting on the
wheels during driving of braking, will generate a moment
around the relevant steering axis, causing the wheel to pull to
the side pull especially at very slow speeds. This moment is
proportional to the size of the offset. As the offset approaches
zero, less moment is generated around the steering axis when
a force is applied to the wheel, and the steering is less
influenced by braking or road shock
Thus, since it has a tendency to maintain or seek a straight ahead position, less positive caster is
needed to maintain directional stability. A vehicle provides stable handling without any defects of
high positive caster because of SAI.

SAI/Camber/IA Troubleshooting Charts (MacPherson Strut type suspension)
SAI

Camber

Included Angle

Problem Area

Equal to Specs

More than Specs

More than Specs

Bent Spindle and/or Strut Body

More than Specs

More than Specs

More than Specs

Strut Tower IN at Top and Spindle or
Strut Bent

Less than Specs

More than Specs

Equal to Specs

Bent Control Arm or Strut OUT at Top

and Bent Spindle or Bent Strut Body

Less than Specs

More than Specs

Less than Specs

Bent Control Arm or Strut OUT at Top
and Bent Spindle or Strut Body

Less than Specs

More than Specs

More than Specs

Bent Control Arm or Strut OUT at Top
and Bent Spindle or Strut Body

Equal to Specs

Less than Specs

Less than Specs

Bent Spindle and/or Bent Strut Body

Less than Specs

Less than Specs

Less than Specs

Strut Top or Bent Control Arm and
Bent Spindle or Strut Body

More than Specs

Less than Specs

Equal to Specs

Strut Tower IN at Top

SAI/Camber/IA Troubleshooting Charts (Double Wishbone type suspension)

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WHEEL ALIGNMENT & ECS

SAI

Camber

Included Angle

Problem Area

More than Specs

Equal to Specs

Less than Specs

Spindle/Knuckle or Upper Control
Arm and/or Control Arm Mount

Less than Specs

Equal to Specs

More than Specs

Bent Lower Control Arm and/or
Lower Control Arm Mount

Equal to Specs

More than Specs

More than Specs

Spindle/Knuckle Assembly

Less than Specs

More than Specs

Equal to Specs

Bent Lower Control Arm

Less than Specs

More than Specs

More than Specs

Spindle/Knuckle Assembly
Bent Lower Control Arm 

Equal to Specs

Less than Specs

Less than Specs

Spindle/Knuckle Assembly

More than Specs

Less than Specs

Equal to Specs

Bent Upper Control Arm

Measuring Procedures
SAI should always be measured after you have adjusted the camber and caster to the proper
specifications or as close to the specifications as possible. Check for worn suspension parts. SAI is
best measured with the front wheels off the ground, brakes applied and alignment equipment
leveled and locked. Raise the vehicle underneath the lower control arms but do not relax the
suspension. Not raising the vehicle from the turntables can cause the control arm bushings to
move when wheels are turned, resulting in an inaccurate reading.
However SAI is typically not adjustable. The most likely cause for SAI being out is bent parts which
must be replaced to correct the condition. A maximum variation side-to-side of ± 1.0° may also
indicate vehicle damage.

SAI

Camber

INCLUDED ANGLE
Included angle is not directly measurable. It is the combination of
SAI and camber. Viewed from the front, the included angle is SAI
plus camber if the camber is positive (Included angle will be
greater than the SAI). If the camber is negative the included angle
is SAI minus camber (Included angle will be less than the SAI).
The included angle must be the same from side to side even if the
camber is different. If a side-to-side variation greater than ± 1.5°
exists, then something is bent, most likely the steering knuckle.
SAI + Camber = Included Angle (I/A)
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Training

Center
[Included
Angle]


WHEEL ALIGNMENT & ECS

STEERING OFFSET
Steering offset, or Kingpin offset is the distance at the road
surface between the tire line and the SAI line extended downward
through the steering axis. The line through the steering axis
creates a pivot point around which the tire turns. Therefore this
distance must be exactly the same from side to side otherwise the
vehicle will pull strongly at all speeds.
Positive steering offset is when the tire contact patch is outside of
the SAI pivot, while negative steering offset is when the contact
patch is inboard of the SAI pivot (front wheel drive vehicles usually
have negative steering offset).

Steering offset (+)
The greater the steering offset (positive or negative), the greater the steering effort and the more
road shock and pivot binding that takes place. When the vehicle has been modified with offset
wheels, larger tires, deflated tires, height adjustments and side to side camber differences, the
steering offset will be changed and the handling and stability of the vehicle will be affected.
Steering offset is designed at the factory and is not adjustable. If you have a vehicle that is pulling
even though the alignment is correct, look for something that will affect steering offset.

SET BACK
Front set back is when one front wheel is set further back
than the other wheel. And rear set back is when one rear

wheel is set further back than the other wheel. Excessive
set-back is normally created by frame or chassis errors.
These errors are brought about in most cases by front
end collision and in some cases by a manufacturing
tolerance error. If the frame is adjusted incorrectly, or
damage is present, it is not unusual to also see a
reduced positive caster reading on the side with the
setback condition.

Set Back

Rear setback may be caused from frame, chassis, and rear chassis mis-alignment due to collision.
If the vehicle has a setback condition, the vehicle may pull to the opposite side of the setback.
Excessive setback can cause an alignment pull to the side with the setback. If the rear axle is
positioned correctly and all other parts and systems of the vehicle are in good working order, a
setback condition will also create different wheelbase measurement side to side.

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Chonan Technical Service Training Center


WHEEL ALIGNMENT & ECS

THRUST ANGLE
Thrust angle is the angle formed by the thrust line and the geometric centerline. The geometric
centerline is a line drawn between the mid-point of the front axle and the mid-point of the rear axle.
If the thrust angle is not zero, then the vehicle will "dog track" and the steering wheel will not be
centered. When toe is different on either of the rear wheels, it creates a thrust angle that causes
rear axle steer. The thrust line dictates the position of the front wheels when driving straight ahead.

It is therefore the most accurate reference when measuring or adjusting the front wheels.
Inspection of the tires can help in diagnosing some wheel alignment failures. The tire wear patterns
associated with improper alignment include single shoulder wear, cupping and feather edging.

Thrust
Angle

Thrust line
Centerline

[ Positive Thrust Angle]

STEERING CENTER
Steering center is simply the fact that the steering wheel is
centered when the vehicle is traveling down a straight and
level road. When setting steering center, the rear toe
should be set first bringing the thrust angle as close to the
vehicle centerline as possible. Then the steering wheel is
locked in a straight ahead position while the front toe is
set. Before locking the steering wheel, the engine should
be started and the wheel should be turned right and left a
couple of times to take any stress off the power steering
valve. Of course, you should always road test the vehicle
after every alignment as a quality control check.

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[ Steering center]

Chonan Technical Service Training Center

WHEEL ALIGNMENT & ECS

TOE OUT ON TURNS
If the right and left steering angles
were the same, they would have the
same turning radius (r1 = r 2), but
each wheel would turn around a
different center, (O1 and O2).
Smooth turning would therefore be
impossible due to side-slipping of
the tires. The result is that, even
though the air pressure in each of
the tires might be equal, and even
though the other wheel alignment
factors might be correct, the tires
would undergo unusual wear.

[At same turning radius (α=β)]

For this reason, the inside front
wheel must steer at a sharper angle
than the outside wheel. This is also
known as the Ackerman effect. In an
actual vehicle, Toe Out On Turns is
accomplished by the steering
linkage is modified in such a way
that the proper steering angles of the
left and right front wheels are

attained, to achieve the desired
turning radii. The steering arm is
either part of the steering knuckle or

[At different turning radius (α<β)]

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Chonan Technical Service Training Center


WHEEL ALIGNMENT & ECS
part of the ball joint and is not
adjustable.
To check toe out on turns, make sure that the readings are at zero on each side when the wheels
are straight ahead and then steer the wheels to the left so that the inner wheel is at 20°, the out
wheel should be less than 20°, optimal reading is 18°. Repeat the test in the other direction, If there
is a problem with the toe-out, it is due to a bent steering arm that must be replaced.

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Chonan Technical Service Training Center


WHEEL ALIGNMENT & ECS

DIAGNOSIS BY VEHICLE SYMPTOM
Vehicle
Symptom

Vehicle
Symptom

Possible Cause
Excessive wheel/rim runout.

Premature
Tire Wear

Power steering reaction bracket loose.

Front End
Shimmy

Tires out of balance.
Incorrect wheel alignment.

Steering gear adjustment loose.

Incorrect tire inflation.

Tires out of balance.

Brakes dragging.

Tires out of round.

Mismatched tires or Radial Pull.
Pulls To
One Side

Frame bent.

Worn steering/suspension components.

Control arm bushing worn.

Ball joint tight or seized.

Power steering valve not centered.

Bent steering knuckle or supports.

Broken or sagging springs.

Damaged suspension components.

Uneven sway bar links.

Front tire pressure low.

Incorrect wheel alignment.

Idler arm bushing too tight.

Incorrect tire inflation.

Power steering fluid low or belt loose.

Wrong tires for vehicle.

Power steering pump defective.

Worn shock/strut.

Steering gear out of adjustment.
Incorrect wheel alignment.

Premature
Tire Wear

Worn or defective shocks/struts.

Steering gear box (rack) mount loose.

Wheel bearings worn or loose.

Hard
Steering

Possible Cause

Vehicle
Wandering

Improper vehicle height.
Rack & Pinion or steering not positioned
correctly.

Incorrect tire inflation.

Stabilizer bar missing or defective.

Suspension/steering system worn.

Worn steering components.

Uneven or sagging springs.

Worn strut rod or control arm bushings.

Improper torsion bar adjustment.

Worn suspension components.

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WHEEL ALIGNMENT & ECS

INTEGRATED FRAME AND BODY (MONOCOQUE)
The integrated frame and body type of construction also referred to as unitized construction,
combines the frame and body into a single, one-piece structure. This is done by welding the
components together, by forming or casting the entire structure as one piece, or by a combination
of these techniques. Simply by welding a body to a conventional frame, however, does not
constitute an integral frame and body construction. In a truly integrated structure, the entire framebody unit is treated as a load-carrying member that reacts to all loads experienced by the vehicleroad loads as well as cargo loads.

+

=

[Integrated frame and body]
Integrated-type bodies for wheeled vehicles are fabricated by welding preformed metal panels
together. The panels are preformed in various load-bearing shapes that are located and oriented so
as to result in a uniformly stressed structure. Some portions of the integrated structure resemble
frame-like components, while other resembles body-like panels. This is not surprising, because the
structure must perform the functions of both of these elements.
An integrated frame and body type construction allows an increase in the amount of noise
transmitted into the passenger compartment of the vehicle. However, this disadvantage is negated
by the following advantages:
-

Substantial weight reduction, which is possible when using a well-designed unitized body

-

Lower cargo floor and vehicle height

-

Protection from mud and water required for drive line components on amphibious vehicles

-

Reduction in the amount of vibration present in the vehicle structure

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