Servicing Manual Steering System

During a turn, centrifugal force causes

body roll. This is the movement of the

vehicle body as it leans out toward the

outside of the turn. The side forces against

the bottom of the tires cause their tops to

tilt toward the inside of the turn. In a left

turn, the result is positive camber of the left

front wheel and negative camber of the

right front wheel.

Camber is a tire wear angle. Any camber,

positive or negative can cause uneven and

rapid tire wear. Tilting the wheel puts more Figure 44 Changes in camber during a left turn.
load and wear on one side of the tire tread. (Ford Motor Company)

Incorrect camber at both wheels can cause hard and unstable steering and wander.

Unequal camber can contribute to low-speed shimmy. Sagging springs can change

camber. When a rear spring sags, it affects the camber of the diagonally-opposite front

wheel. For each one inch (25 mm) of rear-spring sag, the camber of the front wheel can

change as much as ¾ degree.

Steering Axis Inclination

The steering axis is the line around which a
front wheel swings for steering. In figure
45, the steering axis is a line drawn
through the centers of the ball joints. The
steering knuckle pivots about this line to
swing the wheel right or left. On a strut
suspension, the steering axis is a line
drawn through the center of the upper strut
mount and the lower ball joint.
Steering-axis inclination (SAI) is the inward
tilt of the steering from the vertical as
viewed from the front of the vehicle. It is
the angle, in degrees between a vertical
line and the steering axis. The inward tilt is
desirable for three reasons.
1. It helps steering stability by returning

the wheels to straight ahead after a turn
is completed. This is called steering-
wheel returnability.
2. It reduces steering effort, especially if
the vehicle is not moving.
3. It reduces wear.

SAI also helps keep the front wheels rolling

straight ahead. Figure 45 Steering-axis inclination, or SAI (Mazda
Motors of America, Inc.)

The inward tilt of the steering axis causes the front of the vehicle to raise slightly as the

wheels swing away from the straight ahead. When a front wheel is rolling straight ahead,

the outer end of the spindle is at its highest point. As the steering knuckle pivots away

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from the straight ahead, the outer end of the spindle begins to drop. This is because the
spindle and steering knuckle pivot around the steering axis, which is tilted inward.
However, the tire is already in contact with the road and cannot move down any farther.
So the steering knuckle, ball joints, suspension and vehicle body are raised upward. The
tilt is slight—one inch (25 mm) or less. But it is enough for the weight of the vehicle to
help bring the wheels back to straight ahead after completing a turn. This same action
provides steering stability. It tends to make the rolling wheels resist any small force that
tries to move them away from straight ahead.
Steering-axis inclination is not adjustable. It is designed into the steering knuckle. If
camber can be adjusted to specifications, steering-axis inclination usually is correct.
When SAI is not within specifications, the spindle, steering knuckle, ball joints or other
parts are bent or worn. Replace the defective parts.

Scrub Radius

Scrub radius or steering offset is the distance between the steering axis and the tire
contact-area centerline at their intersections with the road surface. If the steering axis
intersects the road surface inside the tire centerline, scrub radius is positive. If the point
is outside, scrub radius is negative. A zero scrub radius means the steering axis and tire
centerline intersect at the road surface.
Scrub radius is not an alignment angle and usually cannot be directly measured.
However, it affects steering effort, stability, and returnability. Rear-drive vehicles with
unequal-length front-suspension control arms often have positive scrub radius. Front-
drive vehicles with MacPherson-strut front suspension usually have negative scrub
radius. This tends to turn the front wheels inward as the vehicle moves forward. It also
helps maintain directional stability is a tire blows out, and helps maintain straight-line
braking if a front-wheel brake grabs or fails. Any unequal forces applied to the steering
act inboard of the steering axis.

Included Angle

The included angle is the camber angle
plus the steering-axis-inclination angle. It is
not an adjustable angle. However, an
improper included angle often indicates a
bent spindle or strut.

.

Figure 46 Included angle is the camber angle plus
the steering-axis inclination (SAI) angle. Positive

camber is shown.

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Caster

Caster is the tilt of the steering axis toward Figure 47 Caster is the tilt of the steering axis
the front or rear of the vehicle. If the tilt is toward the front or rear of the vehicle. Positive
toward the front, the wheel has negative (-)
caster. A rearward tilt provides positive (+) caster (backward tilt) is shown. (Chrysler
caster. Caster is measured in degrees. Corporation)
There are three reasons for using caster
1. To maintain directional stability and Figure 48 Positive caster causes the steering axis
to pass through the road surface ahead of the
control. center of the tire contact area. This causes the
2. To increase steering returnability.
3. To reduce steering effort. steering axis to lead, or pull the tire and wheel along
the road. (Chrysler Corporation)
Directional stability is aided by positive
caster. Figure 49 Effect of sagging springs on caster. (Ford
It covers the steering axis to pass through Motor Company)
the road surface ahead of the center of tire
contact with the road. This places the push
on the steering axis ahead of the road
resistance to the tire. The tire trails behind,
as the positive caster causes the steering
axis to lead or pull the tire and wheel down
the road.
Positive caster tends to keep the wheels
pointed straight ahead. It helps overcome
any tendency for the vehicle to wander or
steer away from straight ahead. However,
negative caster makes steering easier.
Then only steering-axis inclination needs to
be overcome by the driver to steer away
from straight ahead.

Vehicles with power steering often have
more positive caster than vehicles with
manual steering.The positive caster helps
overcome the tendency of power steering
to hold the front wheels in a turn. The
additional positive caster requires greater
steering effort. However, the driver does
not notice because of the power assist.
Positive caster tends to make the wheels
toe out.
Excessive positive caster may cause
increased steering effort, steering-wheel
snapback after a turn, low-speed shimmy
and increased road shock in the steering
wheel. A decrease of positive caster can
result from spring sag. This is one reason
to check the suspension height.

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Toe

Toe is the measurement of how much the wheels point in or out from the straight-ahead
position. The measurement is made in inches, millimeters or degrees. Ideal running toe
is zero. This means the wheels are parallel while rolling straight ahead. When the wheels
point in, toe is positive (+). The amount the wheels point inward is toe-in. If the wheels
point out, toe is negative (-). The amount the wheels point out is toe-out. Zero toe means
the wheels run parallel. They are the same distance apart at the front as they are at the
rear.
Toe is set with the vehicle standing still. Typically, the front wheels of a rear-drive vehicle
are given a slight toe-in of about 1/8 inch (3mm). When the vehicle moves forward, road
resistance usually causes the front tires to spread apart or toe out. This compresses the
steering linkage and takes up any play. As a result the tires become parallel and roll
straight ahead with zero toe. On some front-drive vehicles, the front tires tend to pull in
as the vehicle moves forward. These vehicles are often given a small amount of toe-out.
A tire has to move in the direction the vehicle is traveling. Any toe-in or toe-out drags the
tire sideways as it rolls. The greater the toe or toe angle, the faster the tire wears. Zero
toe allows the tires to roll straight ahead, with neither toe-in nor toe-out.

Turning Radius

Turning radius is the difference in the Figure 50 Turning radius, or toe-out-on-turns. (Hunter
angles of the front wheels in a turn. It is Engineering Company)
also called toe-out on turns and turning
angle. During a turn, the two front wheels
travel on concentric circles which have a
common center. The inner wheel turns
through a greater angle and follows a
smaller radius than the outer wheel. This
is because the outer wheel must travel a
greater distance and make a wider turn
than the inner wheel.
In figure 50, when the inner wheel turns at
an angle of 20 degrees, the outer wheel
turns 8 degrees. The inner wheel toes out
more to reduce tire scrub (scuffing) and
wear.

This difference in toe-out on turns is achieved by the proper relationship among the
steering arms, tie rods and steering gear. The inner- and outer-wheel angles should not
vary more than 1.5 degrees from specifications. If turning radius is not within
specifications, check for a bent steering arm or tie rod.

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Setback

Wheel setback is the difference in vehicle Figure 51 Setback or difference in vehicle wheelbase
wheelbase from one side to the other from one side to the other. (Ford Motor Company)
(Figure 51). It occurs when one wheel is
behind the other wheel on the same axle.
Setback results from production
tolerances during vehicle manufacture
and from collision or impact damage. It
can also result from improper placement
of the engine cradle or subframe. A
vehicle will drift or pull toward the side
with the shorter wheelbase.
Setback of more than ¾ inch (19 mm) is
excessive.

It usually indicates bent parts. Excessive setback also causes the center point of the
steering gear to be off. Correct any problem with excessive setback before performing a
wheel alignment.

Thrust Angle

When all four wheels are properly aligned Figure 52 Thrust angle on a vehicle with (A) a live
and the steering wheel is centered, the rear axle and (B) independent rear suspension.
vehicle should travel forward in a straight (Ford Motor Company)
line. However, if a rear wheel has improper
alignment or setback. When the vehicle
moves forward it may not move straight
ahead. The direction of travel is determined
by three lines that run the length of the
vehicle. These are the vehicle centerline,
the geometric centerline that connects the
midpoints of the front wheels and rear
wheels. The thrust line is a line from the
midpoint between the two rear wheels. It
determines the direction the vehicle will
travel if unaffected by the front wheels.
If the thrust line makes a 90-degree angle
with the rear-axle centerline, the thrust line
falls on or coincides with the vehicle
centerline.

The vehicle will travel straight ahead. If the thrust line does not coincide with the vehicle
centerline, a thrust angle is formed between the centerline and the thrust line. The thrust
line then represents the path the vehicle will try to take. This condition is also called
tracking.
The thrust angle affects handling by causing a pull in the direction away from the thrust
line. In a rear-drive vehicle, this may be caused by chassis damage or improper
positioning of the rear axle. Also, independent rear suspensions can have unequal toe
adjustments on the rear wheels. The result can be tire wear similar in appearance to
wear caused by improper toe.

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INSPECTING STEERING AND SUSPENSION COMPONENTS

INSPECTING STEERING LINKAGE

Looseness in the
steering linkage can
cause wheel shimmy,
uneven braking
problems, and
excessive tire wear. To
check fro loose
steering linkage, turn
off the air-suspension
switch (trunk switch) on
vehicle with air springs.

Figure 53 An air suspension system with air springs at all four wheels.
(Chrysler Corporation)

Raise the vehicle until the front tires clear the floor. Start the engine if the vehicle has
power steering. [Use a brake-pedal depressor or have an assistant apply the foot or
service brakes. This eliminates any play caused by loose wheel bearings.

Grasp both tires at the front and push out
and then pull in. On vehicles with 16-inch
(406 mm) diameter or smaller wheels, the
maximum movement at the front or rear of
each tire should be ¼ inch (6.5 mm) or
less. Excessive tire movement indicates
worn linkage parts such as wear in the tie-
rod ends or rack ball socket. Replace the
defective parts and any tie-rod end that has
torn boot. Then align the wheels.

Another method of checking the steering Figure 54 Inspecting steering linkage. (Ford Motor
linkage is the dry-park check. Park the Company)
vehicle on a dry surface with the weight on
the wheels.

With the engine off and the steering wheel unlocked, watch the various connecting parts
when the steering wheel is moved. Movement between the tie-rod end and the steering
arm indicates a worn tapered-hole in the steering arm or loose ball-stud in the tie-rod
end. Check each tie-rod end and other wear points for excessive looseness, binding and
roughness.

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CHECKING STEERING GEARS

When there is excessive looseness in the steering, find out if the looseness is in the
steering gear. Sometimes a steering-gear adjustment eliminates the looseness.
However, an adjustment cannot correct for defective bearing or excessive wear.

1. Recirculating-ball steering gear.
With the wheels on the floor, turn the steering wheel one way and then the other. If
excessive steering-wheel movement is required to move the pittman arm, the steering
gear is worn or needs adjusting. Two adjustments on the recirculating ball steering
gear are the worm-bearing preload and the overcenter preload. The worm-bearing
preload takes up the worm-shaft ensplay. The overcenter preload removes backlash
between the worm and the sector gear. These adjustments are usually made on the
steering gear after removing it from the vehicle.

2. Rack-and-pinion steering gear.
The rack is supported at two points in the housing. The rack bushing supports the
right end. The rack yoke supports the left or control-valve end. A spring behind the
yoke pushes the rack into the pinion. This rack-to-pinion preload is the rack-yoke
clearance. It maintains the proper mesh between the pinion and the rack. The rack
housing includes an adjuster plug, screw, or shim pack for adjusting rack-yoke
clearance.

Figure 55 Construction of rack-and-pinion power steering gear. (Moog Automotive, Inc.)

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CHECKING WHEEL BEARING

Wheel bearings are usually either ball or
tapered-roller bearings. These may be
adjustable or non-adjustable. The front hubs of
rear-drive vehicles and the rear hubs of front-
drive vehicles are often supported by two
adjustable roller bearings. The inner bearing
and outer bearing mount on the stationary
spindle and should have no preload. Front-
drive vehicles have two ball or tapered-roller
bearings in each steering knuckle. These
bearings are permanently lubricated and not
adjustable.

1. Checking adjustable wheel bearings Figure 56 Adjustable wheel bearings in the hub
Turn off the air-suspension switch (trunk of a non-driving wheel. (Chrysler Corporation)
switch) on vehicles with air springs.

Raise the vehicle until the tires clear the
ground. Support the vehicle so the ball
joints are loaded. This means they are
carrying the weight of the vehicle. Grasp
the tire at the top and bottom and rock it in
and out. If the outer edge of the tire moves
more than 1/8 inch (3 mm), have an
assistant apply the brakes and rock the tire
again. If this eliminates the movement, the
wheel bearings are loose.

2. Checking non-adjustable wheel bearings

To check non-adjustable wheel bearings on

General Motors and other vehicles, raise Figure 57 Non-adjustable wheel bearings used
the tires off the ground. with strut suspension. (Toyota Motor Sales

USA, Inc.)

Remove the wheels and the disc-brake calipers or brake shoes. Install two wheel

nuts to hold the drum or disc in place. Mount a dial indicator against the hub.

Measure the endplay while pushing in and pulling out on the drum or disc. If the

endplay exceeds 0.005 inch (0.13 mm), replace the hub-and-bearing assembly. The

wheel bearings cannot be replaced separately.

INSPECTING BALL JOINTS

Various methods are used to check ball joints. Some have built-in wear indicators. In
others, the amount of wear is measured. Replace any ball joint that has a torn boot.

1. Wear-indicating ball joints
Many ball joints have a built-in wear indicator in the cover. This is slightly protruding
boss into which a grease fitting may be threaded. On a new ball joint, the boss
protrudes 0.050 inch (1.27 mm). It recedes into the cover as the ball joint wears. To
check a wear –indicating ball joint, the weight of the vehicle should be on the wheels

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so the ball joints are loaded. Wipe the grease fitting and boss to remove all dirt and
grease. Observe the cover, or scrape a fingernail, steel scale, or screwdriver across
it. If the boss is flush with or inside the cover, the ball joint is worn and should be
replaced.
Similar check of the lower ball joints is
made on Chrysler front-wheel-drive
vehicles. However, the wear indicator is
that the grease fitting loosens as the
ball joint wears. With the weight of the
vehicle on the wheels, try to move the
grease fitting with your fingers. Replace
the ball joint if the grease fitting has any
movement.

2. Ball joints without wear indicators

To check ball joints without wear

indicators, raise the front end. Support

the vehicle at the proper points to

remove the load from the ball joints.

Attach a dial indicator to the control

arm. Place the dial indicator plunger

against the steering knuckle or pinch-

bolt around the ball-joint stud. The dial

indicator will show any movement

between the ball-joint stud and its

socket.

Check vertical movement by lifting the

tire and wheel with a pry bar while

observing the dial indicator. Some ball

joints are preloaded with rubber or

springs under compression. They

should have very little vertical

movement. These ball joints are

marked as preloaded in specification Figure 58 Support points for checking ball joints in
tables. various coil-spring front-suspension systems.

Check horizontal movement by grasping the top and bottom of the tire, and moving it

in and out. More horizontal movement as indicating ball-joint wear. Replace the ball

joint if either vertical or horizontal movement exceeds the manufacturer’s

specifications. Then check the wheel alignment.

CHECKING SHOCK ABSORBERS AND STRUT DAMPERS

One test of shock absorbers and strut dampers is the bounce test. Bounce the vehicle at
each corner by pushing down and releasing it. The vehicle should return to its original
height and stay there. If it continues to bounce up and down, the shock absorber or strut
damper is probably defective and should be replaced. Check the shock absorber or strut
for wetness and leaking fluid. A shock absorber or strut damper that has lost fluid will not
work properly and should be replaced. The units are sealed and fluid cannot be added.

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STEERING AND SUSPENSION SERVICE

SERVICING STEERING AND SUSPENSION

After inspecting the steering and suspension, correct any defects found before starting a
wheel alignment. Follow the procedures in the vehicle service manual. Servicing the
steering and suspension includes:

• Removal, installation and adjustment of tie rods.
• Removal and installation of other steering-linkage parts.
• Removal and installation of steering gears.
• Removal and installation of ball joints and control arms.
• Removal and installation of struts and shock absorbers.
• Removal and installation of wheel hubs.
• Installation and adjustment of wheel bearings.

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Qualification : Automotive Servicing NC II

Module Title : Servicing Manual Steering System

Learning Outcome #3 : Perform wheel balancing

Assessment Criteria :

1. Wheel balancing machine is set-up.
2. Wheel weight location and size are identified.

Resources :

• Automotive Mechanics Pp. 675 - 710
10th Edition Pp. 749 - 762
Crouse and Anglin
Pp. 1 - 70
• Power Train and Under Chassis
Course Manual Pp. 1 - 12
Pp. 96 - 97
• Nissan Diesel Chassis Repair Manual
Model CK 20 – TK 20 Series Vol.2

• Mathematics II SEDP Series

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LEARNING EXPERIENCES

Learning Outcome #3 : Perform wheel balancing

Learning Activities Special Instructions

• What are the equipment used in wheel • For more information about balancing the

balancing wheel read references listed below

Your first task on this activity is to setup the

tire balancing machine.

1. Identify wheel deformities.

1.1 Read • Automotive Mechanic

a. Wheel runout Crouse – Anglin

b. Wheel balance Pp. 760 – 765

¾ Your next task is to have a review on
tire and wheel repair.

2. Review on tire and wheel repair. • Automotive Mechanic
2.1 Read Crouse – Anglin
a. Tire repair Pp. 761 – 763
b. Temporary tubeless tire repair
c. Tubeless tire repair
d. Wheel repair

¾ What science/math concept would • Mathematics II
help you understand wheel balance? SEDP series

Pp. 96 - 97

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Qualification : Automotive Servicing NC II
Module Title
Learning Outcome #4 : Servicing Manual Steering System
Assessment Criteria
: Conduct wheel alignment

:

1. Steering and suspension component conditions
accurately prior alignment.

2. Wheel alignment equipment positioned/installed as per
manual instruction.

3. Equipment reading interpreted accurately and required
adjustment done as per manufacturer specification.

4. Wheel alignment is adjusted

Resources :

• Automotive Mechanics 10th Edition

Crouse and Anglin pp. 675 - 690

pp. 691 - 710

• Nissan Diesel Chassis Repair Manual
Model CK 20 – TK 20 Series vol. 2, pp. 5 - 8

• The Automotive Drive Trains and Chassis Unit

Felizardo Y. Francisco pp. 125 - 134

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LEARNING EXPERIENCES

Learning Outcome #4 : Conduct wheel alignment

Learning Activities Special Instructions

• Do you have an experience in • For more information about conduct

conducting wheel alignment? wheel alignment read references listed

• What are the procedures in conducting below.

wheel alignment?

• What are the component parts of wheel

alignment?

1. Correct sequence in conducting • Power Train and Under Chassis

steering and suspension alignment. Course Manual

1.1 Read on procedure in Pp. 1 –70

conducting steering and

suspension alignment.

1.2 Familiar on the component • Automotive Mechanic

parts of wheel alignment. Crouse & Anglin

Pp 675 – 710

¾ After knowing the procedure

and familiarization of • Nissan Diesel Chassis

component parts has a self – Repair Manual

check. Refer to the answer Pp 1 – 70

key for your answer.

¾ What Math concept can help

us understand the actual • Task Sheet Template

wheel alignment?

¾ Let us consider the next

activity and find out the math

concepts relevant to wheel

alignment.

1.3 Perform task sheet an Angles • Automotive Mechanic

and degrees. Crouse & Anglin

¾ After performing 1.3 be sure Pp 675 – 710

to have a self – check with • Power Train and Under Chassis
your instructor.
Course Manual

Pp. 1 –70

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2. Correct reading / interpreting of

wheel alignment / equipment for

adjusting.

2.1 Perform actual adjustment • Automotive Mechanic

and refer to repair manual on Crouse & Anglin

wheel alignment adjustment. Pp 675 – 710

¾ After performing the activity,
have your instructor check
your works, and answer the
questions in the self – check.

3. Record data on steering alignment
inspection.

¾ Fill out data on the checklist • Automotive Mechanic

for referral on the next Crouse & Anglin

alignment. Pp 675 – 710
¾ Stored data on the

storeroom.

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CHECKING TIRE AND TIRE PRESSURE

TIRES AND TUBES

Purpose of Tires Figure 59 A tire-and-wheel assembly. The tire is the
The automotive chassis includes the brake, only contact between the vehicle and the road
steering, and suspension systems. The surface. (Bridgestone Tire)
chassis components that drive the vehicle
and support its weight are the wheels and
tires. Only the vehicle tires have contact
with the road surface.
Tires have two functions. First they are
airfilled cushions that absorb most of the
shocks caused by road irregularities. The
tires flex as they meet those irregularities.
This reduces the effect of road shocks on
the vehicle, passengers, and load. Second,
the tires grip the road to provide good
traction. This enables the vehicle to
accelerate, brake and make turns without
skidding.

Types of Tires
There are two types of ties: tube and
tubeless. Tube tires have an inner tube
inside the tire. This is a round rubber
container that holds the air which supports
the vehicle. Both the tube and tire mount
on the wheel rim. The tire valve is part of
the tube and protrudes through the rim.
Compressed air is forced through the valve
to inflate the tube. The air pressure in the
tube then causes the tire to hold its shape.
Tubes are used in some truck and
motorcycle tires. Tubes are seldom used in
passenger and light-duty vehicles. Most
automotive vehicles use tubeless tires. The
tire mounts on an airtight rim so air is
retained between the flange and the tire
bead.

Figure 60 Tire and rim cut away to show the tube.
(ATW)

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Tire Construction Figure 61 In a tubeless tire, the tire bead rests
The tire casings for tube and tubeless tires are between the ledges and flanges of the rim to
made in the same way. Layers of cord or plies
are shaped on a form and impregnated with produce an airtight seal. (ATW)
rubber. The tire sidewall and treads are then
applied. They are vulcanized in place to form
the tire. To vulcanize means to heat the
rubber under pressure. This molds the tire into
desired form.
The number of cord layers or plies varies.
Passenger-car tires have 2, 4, or 6 plies.
Heavy-duty truck and bus tires may have up to
14 plies. Tires for heavy-duty service, such as
earth-moving machinery, may have up to 32
plies.
All tires do not have the same shape or profile.
The aspect ratio or profile ratio differs. This is
the ratio of a tire's section height to section
width. Three aspect ratios are 80, 70, and 60.
The lower the number, the wider the tire
appears. A 60-series tire is only 60 percent
high as it is wide.

Bias and Radial Plies

Plies can be applied two ways: diagonally or

radially. For many years, most tires had diagonal

or bias plies. These plies crisscross. This makes

a tire that is strong in all directions because the

plies overlaps, However, the plies tend to move

against each other and produce heat, especially

at high speed. Also, the tread tends to close or

"squirm' as it meets the road. Radial tires were

brought out to remedy these problems. In a radial

tire, the plies run parallel to each other and

vertical to the tire bead. Stabilizer belts are

applied over the plies to give strength parallel to

the beads. Belts are made of rayon, nylon,

fiberglass, or steelmesh. Figure 62 Construction of a tubeless radial

tire. (Ford Motor Company)

All new cars and most light-duty vehicles

have radial tires. The radial-tire sidewall is

more flexible than the bias-ply. Therefore,

the radialtire tread wraps around the edge

of the tire to compensate for the flexible

sidewall. The result is that the radial tread

does not hell up as much when the Figure 63 Three aspect ratios of car tires. The lower
vehicle rounds a curve. This keeps more the number the wider the tire appears. (ATW)
of the tread on the road and reduces the

tendency of the tire to skid.

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The radial tire provides better fuel economy than a bias-ply tire. This is because the
radial has less rolling resistance and less engine power is required to roll the tire. The
radial also wears more slowly. It has less heat buildup and the tread does not squirm as
the tire meets the road.
Some bias-ply tires are belted. These tires are bias-ply tires to which stabilizer belts have
been added under the tread.

Figure 64. Three basic tire constructions (Firestone Rubber Company)

Tire Tread Figure 65 The difference in the amount of tread a bias
Tire tread is part of the tire that meets tire and a radial tire put on the road during a turn.
the road. It has a raised pattern molded
into it. There are many designs,
depending on the intended use of the
tire. Many passenger vehicles use mud-
and-snow tires. These can be identified
by M+S or M&S molded into the
sidewall. They provide quiet running with
good traction in mud and snow.

Mud and snow tires are used on four-wheel-drive pickup trucks. Its tread pattern is
deeper and wider or "more aggressive" than normal tread designs. This provides better
mud-and-snow traction with acceptable wear on paved surfaces. The tread compound is
also designed to resist tearing and chunking.
The treads shown are symmetric and nondirectional. "Nondirectional" means the tire can
run equally well in either direction. The tire can be installed with either sidewall facing
out. The tire must be installed for forward rotation in the direction of an arrow on the
sidewall.

Directional and asymetric sports car tread are used as the rear of the Chevrolet Corvette.
"Asymetric" means the inside half of the tread is not the same as the outside half. The
tire is installed on the side of the car marked on the sidewall, and with the specified
direction of forward rotation. This tire provides better braking and handling characteristics
than a comparable symmetric, nondirectional tire. Different size tires are used at the front
and rear of the Corvette. As a result, each tire is position specific. It can run only in a
specified wheel-position on the car. Other tires are classified as snow tires, studded tires,

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and off-road tires. Snow tires have large rubber cleats that cut through snow to improve
traction. Studded tires have steel studs that stick out above the tread. These improve
traction on ice and snow. However, many states regulate or ban studded tires because of
possible damage to the road surface. A variety of off-road tires are available. These often
have tread patterns using knobs or cleats. Off-road tires usually make noise and wear
prematurely when driven on the highway.

Figure 66 Types of tire tread. (Goodyear Tire and Rubber Company)

Some tires use two different compounds in the tread. Con compound is softer than the
other for improved traction. In general, the softer the compound, the better the traction.
The harder the compound, the longer the tread life.

Tire Valve
Air is put into the tire or tube trough a spring-loaded tire valve or Schrader valve. On tube
tires, the valve is on the inner tube and sticks out through a hole in the rim. Tubeless
tires use a separate tire valve mounted in a hole in the rim.
Spring force and air pressure hold the tire valve in its normally-closed position. A cap is
usually threaded over the valve stem end to protect it from dirt. The cap also keeps
guard against air leaks. Some tire valves have a non-movable valve core. The core is
three-pronged white plastic. A special deflator is required to let air out of the tube.

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Tire pressure
The amount of air pressure in the tire
depends on the type of tire and how it is
used. Passenger-car tires are inflated from
about 22 to 36 psi (152 to 248 kPa).
Heavyduty tires for trucks and buses may
be inflated to 100 psi (690 kPa). The
maximum inflation pressure is marked on
the tire sidewall. A tire placard or tire
information label lists the recommended
inflation pressure for each tire.
This label is usually located on a door
edge or door jamb, or inside the glovebox
door. The label also lists maximum load
and tire size (including spare). Running the
tires at the specified pressure helps
provide better vehicle handling while
avoiding premature tire wear.
Underinflated tires wear on the outsides of
the tread.
Also, the tires flex excessively which
produces extra heat and more rapid wear.
Overinflation causes the center of the
tread to wear. The tire cannot flex normally
and this puts stress on the sidewalls and
plies.

Tire Pressure Monitoring Figure 67 A tire placard or information label lists the
Some vehicles have an electronic low-tire recommended inflation pressure for each tire on the
pressure warning system (TPWS). This
system senses or monitors the tire vehicle. (Ford Motor Company)
pressure in a moving vehicle. When the
pressure drops in a tire, an Figure 68 A tire-pressure sensor on the wheel inside
instrumentpanel light illuminates to alert the tire, which signals when the tire pressure is low.
the driver. A tire-pressure-sensor and
transmitter mounts inside the tires on each (EPIC Technologies, Inc.)
wheel. When the tire pressure fall below
25 psi (172 kPa), the tire pressure sensor
sends a radio signal to the receiver-control
module in the instrument panel. This turns
on the
LOW TIRE PRESSURE light.
The receiver-control module also has
selfdiagnostic capabilities and can store
fault codes. If no signal is received from a
tirepressure sensor, the control module
turns on a SERVICE LTPWS light

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The tire-pressure sensors are peizoelectric devices and do not need batteries. In a
piezoelectric device, a small voltage appears across a crystal when a pressure is
applied. In the tire-pressure sensors, the vibration produced by the rolling tire generate
the voltage. Therefore, the system works only when the vehicle is moving or the tire is
being vibrated.

Tire Size and Sidewall Markings
The format for the metric tire-size designation found on most tires is shown. Various
letters and numbers may appear in each position. Each marking has a special meaning.

TIRE INSPECTION
Cautions for Servicing Tires
Several cautions must be followed to avoid personal injury and to prevent damage to the
wheel and tire.

1. Matching tire and wheel width. Do not
try to install a narrow tire with a high-
aspect ratio on a wide rim. For
example, a tire with an 80 aspect ratio
must not be installed on a wide rim that
requires a 60 tire.

2. Matching tire and wheel diameter. Do

not try to mount a 16-inch tire on a

16.5-inch wheel, or a 15-inch tire on a

15.5-inch wheel. The result could be a

deadly explosion when inflating the tire. Figure 69 Wheel with locking wheel cover and lock
Check the rim size. It may be stamped bracket. The special key wrench is needed to
near the center of the wheel disc. remove or install the lock bolt. (Ford Motor

Company)

3. Mixing tires. All tires on a vehicle should be the same size, construction (radial or

non-radial), and speed rating unless otherwise specified by the vehicle manufacturer.

If two radials and two non-radials are on the vehicle, put the radials on the rear. Snow

tires should be installed in pairs on the drive axle (either front or rear), or on all four

wheels. Never put non-radial (bias or belted-bias) snow tires on the rear if radials are

on the front. Match tire sizes and construction on four-wheel drive vehicles. Tires

affect vehicle stability and handling. Mixing tires may cause handling problems.

4. Respecting compressed air. A terrific force is contained in an inflated tire. An
explosion of the tire-and-wheel assembly can result from improper or careless
mounting procedures. Never stand over a tire while inflating it. If the tire explodes, the
sudden release of compressed air has enough energy to throw a person more than
30 feet (9 m) in the air. People have been seriously injured or killed by exploding
tires.

5. Protecting your eyes Wear eye protection (safety glasses, safety goggles, or a face
shield) when demounting and mounting tires. When deflating a tire, avoid the air
stream from the tire valve. The air comes out at high speed and can blow dirt or
debris into your eyes.

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Checking Tire Pressure and Inflating Tires
Before checking tire pressure and adding air, know the correct pressure for the tire. The
specification is in the owners manual and on the vehicle tire-information label. When the
vehicle is carrying a heavy load, pulling a trailer, or driving at sustained highway speed,
higher tire pressure may be necessary. Maximum pressure should never exceed the
maximum pressure marked on the tire sidewall.
Inflation pressure is given for a cold tire. Pressure increases as tire temperature rises.
Highway driving on a hot day can increase the tire pressure from 5 to 7 psi (35 to 48
kPa). As the tire cools, it loses pressure. Never bleed a hot tire to reduce its pressure.
The pressure will then be low when the tire cools. Install the cap on the tire valve after
checking pressure or adding air.

Tire Inspection
The purpose of inspecting tires is to determine if they are safe for further use. When
defects or improper wear patterns are found, inform the driver. Recommend the services
that will correct the cause of the abnormal wear.
Tires have tread-wear indicators or wear bars. These are filled-in sections of the tread
grooves that will show when the tread has worn down to 1/16 inch (1.6 mm). A tire with a
wear bar showing is worn out and should be replaced. Too little tread remains for
continued safe driving. A tread-depth gauge can be inserted into the tread grooves to
measure tread depth of at least 1/32 inch (0.8 mm) in any two adjacent grooves at any
location on the tire.
Check for bulges in the sidewalls. Bulges mean plies have separated and the tire could
fail at any time. Tires with separated or broken plies should be replaced.

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Qualification : Automotive Servicing NC II
Unit of Competency : Service Steering System
Module Title : Servicing Manual Steering System
Name of Task Sheet : Measurement of angles
Learning Outcome : Conduct wheel alignment

Equipment and Resources:

5. Mathematics an Integrated Approach.
6. Protractor, Pencil and Calculator

Procedure :

One system of measurement a complete revolution is divided into 360 equal parts,
each of which is called a degree of rotation or simply a degree. If the rotation is
counterclockwise, the measure is ordinarily taken as positive. If the rotation is clockwise,
the measure is negative.

Y mla = -40
mla = 320
B
O

+320 a
Degrees can be divided into decimal degrees. Each
degree can be divided into 60 equal parts called
minutes (denoted by ’) and each minute can de divided
into 60 equal parts called seconds (denoted by “ ).
Thus,

10 = 60’ and 1’ = 60”

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The equal sign is used to indicate that we have written 2 names for the same
amount of rotation.

Step one: Find the degree measure of an angle formed by rotation of:

a) 1 ¾ revolution clockwise b) 17/34 revolution counterclockwise

Step two:
a) 1 ¾ (-360 ) = - 6300
b) 17 / 32 (3600) = 191.250, or 1910 15’

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Terms and Definitions

¾ Diagnosis – a conclusion arrived ¾ Steering system - the
mechanism that enables the
at through critical perception or driver to control the direction of
the vehicle travel.
scrutiny, hence, keen
¾ Power steering – a steering
understanding of appearances. It system that uses hydraulic
pressure from a pump, or from
includes a conclusion as to what an electric motor, to multiply the
driver’s steering force.
has already happened, or a
¾ Tie – rod – in the steering
recommendation of what should be system, an adjustable – length
rod that, as the steering wheel
done. turns, transfer the steering force
and direction from the rack or
¾ Caster – the forwarded or linkage to the steering arm.

backward tilt of the kingpin from ¾ Wheel – a disc or spokes with a
hub (revolving around an axle) at
vertical the center and a rim around the
outside for mounting the tire.
¾ Camber – the inward or outward
¾ Kingpin inclination – the
tilt of the front wheels from vertical. inclination or the inward tilt of the
kingpin or centerline of the
¾ Front – end geometry – the ballpoint from vertical.

angular relationship between the

front wheels, wheel attaching

parts, and vehicle body or frame.

Includes camber, caster, steering

axis inclination, toe, and turning

radius.

¾ Steering axis inclination – the

inward tilt of the steering axis from

the vertical as viewed from the

front of the vehicle.

¾ Steering axis – the line around

which a front wheel swings for

steering.

¾ Toe – the amount, in inches,

millimeters, or degrees, by which

the front of a wheel point inward

(toe – in) or outward (toe – out).

¾ Turning radius – the difference in

the angles of the front wheels in a

turn; the inner wheel toes out

more. Also called toe – out on turn.

¾ Wheel alignment – a series of test

and adjustments to ensure that the

wheels and tires are properly

positioned with the road and with

each other.

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