Wheel_Alignment Handouts

Diagnosis Technicain - Suspension and Steering

Wheel Alignment

Description

Description

Caster Camber

Toe

Steering axis inclination

Turning radius

The vehicle must have proper straightline performance for stable driving, cornering performance for driving around curves, recovery force for returning to the straight-line condition, the capacity to soften the shock transmitted to the suspension when the tires are impacted, etc. Therefore, the wheels of a vehicle are mounted at specific angles to the ground and specific suspensions for each purpose. This is called wheel alignment. The wheel alignment has the following five factors: • Camber • Caster • Steering axis inclination (kingpin inclination) • Toe (toe-angle, toe-in and toe-out) • Turning radius (wheel angle, turning angle) If even one of these elements is incorrect, the following problems can occur: • Difficult steering • Poor steering stability • Poor recovery on curves • Shortened tire life (1/1)

©2003 TOYOTA MOTOR CORPORATION. All right reserved. -1-


Wheel Alignment

Camber

Description 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". In early automobiles, the wheels were given positive camber in order to improve the durability of the front axle, and to cause the tires to contact the road surface at right angles to prevent uneven tire wear on roads where the center of the road is higher than the edge. In modern automobiles, the suspension and axles are stronger than in the past and road surfaces are flat, so there is less need for positive camber. As a result, tires are being adjusted more toward zero camber (and there are some vehicles with zero camber). In fact, negative camber is now commonly employed in passenger cars to improve cornering performance.

0 Negative

Positive Camber

Camber

90

Uneven wear of tire Exce Excess ss on posit positiv ive e side side

Exce Excess ss on nega negati tive ve side side

Outside

Inside

Outside

Inside

SERVICE HINT: If the wheels are given ex cessive positive or negative camber, this causes uneven tire wear. If the wheels are given ex cessive negative camber, the tires wear quicker on the inside; if the wheels are given excessive positive camber, the tires wear quicker on the outside. (1/1) Negative Camber

Camber thrust

Positive camber

Negative camber

Inside

Outside

Load

O

Camber thrust

Inside

Outside

Load

Camber thrust

O

When a vertical load is applied to a cambered tire, force is generated in the horizontal direction. This force is called "camber thrust" and operates to the inside of the vehicle for negative camber and the outside of the vehicle for positive camber. During cornering, because the vehicle leans to the outside, the tire camber becomes more positive, the camber thrust to the inside of the vehicle is reduced, and cornering force is reduced. The negative camber suppresses the positive camber of the tires during cornering and helps maintain proper cornering force.

(1/1)

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Wheel Alignment

Camber During Cornering Negative camber

When a vehicle turns a corner, the camber thrust on the outside tires acts to reduce the cornering force due to the increase in positive cambe r. Centrifugal force tilts the turning vehicle due to the action of the suspension springs, changing the camber.

Centrifugal force

Small positive camber Straight-ahead driving

Cornering force

Positive camber

Centrifugal force

Large positive camber Straight-ahead driving

Cornering force

HINT: Cornering is always accompanied by centrifugal force, which tires to force the vehicle to turn in a larger arc than intended by the driver unless the vehicle can generate a sufficient counterforce - that is, centripetal force - to balance this. This centripetal force is generated by the deformation and side-slipping of the tread that occurs due to friction between the tire and the road surface. This called cornering force. (1/1)

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Wheel Alignment

Zero Camber and Positive Camber Zero camber

Positive camber Reduction of vertical load

Prevention of wheel slip-off

F F1

Spindle F2

F F’

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Zero camber The main reason for adopting zero camber is that it prevents uneven wear of the tires. If the wheels are given negative or positive camber, the inclination of the tires relative to the road surface generates a difference in the rotation radii for the inside and outside of the tires when the tires rotate and the tires wear unevenly. Zero camber prevents this. Positive camber The roles of positive camber are as follows: • Reduction of vertical load In case of zero camber, the load to the spindle is applied to F’ direction. Load F’ applied to the spindle changes to load F applied to the direction of the spindle joint by attaching the positive camber. Therefore, the moment load applied to the spindle and steering knuckle is decreased. • Prevention of wheel slip-off Load F against the wheel can be divided into F1 and F2. F2 is a force for the direction of spindle axis and pushes the wheel inside. This force prevents the wheel from slipping off from the spindle. • Prevention of undesirable negative camber due to road This prevents the top of the wheel from inclining inward due to deformation of the suspension components and bushings caused by the load of the passengers and cargo. • Reduction of steering effort This is explained in detail in the section on steering axis inclination. (1/1)


Wheel Alignment

Caster and Caster Trail

Description Caster is the forward or backward tilt of the steering axis. Caster is measured in degrees from the steering axis to vertical as viewed from the side. Backward tilt from the vertical line is called "positive caster", while forward tilt is called "negative caster". The distance from the intersection of the steering axis centerline with the ground, to the center of the tire-to-road contact area is called "caster trail". The caster angle affects the straight-line stability and the caster trail affects the wheel recovery after cornering.

Positive

Negative 0

Caster

Front Caster angle

SERVICE HINT: If the wheels are given ex cessive positive caster, the straight-line stability is improved, but cornering becomes difficult.

90

Caster trail

(1/1)

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Wheel Alignment

Straight-line Stability and Wheel Recovery

Straight-line stability due to caster angle

without Caster angle

with Caster angle

Wheel recovery due to caster trail

Jack-up torque

Front

P

P’ T’

T

a’

a

O’

O

Trail

F

Caster trail

P, P’ a, a’ O, O’ F, F’ F1, F2 F’1, F’2 T, T’

: : : : : : :

F ’1

F ’2

F2

Front

F1

F’

Driving force Steering axis Center of tire-road contact area Reactive force Composite force F Composite force F ’ Recovery force

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• Straight-line stability due to caster angle When the steering axis rotates, during cornering, if the wheels have caster angle, the tires are inclined relative to the ground and jack-up torque is generated that attempts to lift the vehicle body as in the figure. This jack-up torque functions as a recovery force that attempts to return the vehicle body to the horizontal and maintains the straight-line stability of the vehicle. • Wheel recovery due to caster trail If the wheels are given caster angle, the contact point of the line extending from the steering axis is forward of the center of tire-road contact. Therefore, since the tires are pulled from the forward direction, the force pulling the tires holds down the force attempting to destabilize the tires and maintains straight-line performance. Also, when the tires face sideways due to steering or disturbance during straight-line travel, side forces (F2 and F' 2) are generated. These side forces act as rotation forces around the steering axis due to the caster trail and are forces attempting to return the tires to their original positions (recovery force). At this time, if the caster trail is long, for the same magnitude side force, a larger force works to return the steering wheel. Therefore, the longer the caster trail, the greater the straightline performance and recovery force. (1/1)


Wheel Alignment

Nachlauf and Vorlauf Geometry Offset

Steering axis

Large change in trail Nachlauf geometry

Offset

Caster trail Ordinary geometry

In general, the caster angle must be increased in order to increase caster trail. However, even if the caster angle remains the same, the caster trail can be set as desired by offsetting the steering axis to the front or rear from the wheel center. Nachlauf geometry enables caster trail to be increased by offsetting the steering axis to the front from the wheel center. Vorlauf geometry enables caster trail to be decreased by offsetting the steering axis to the rear from the wheel center. In actual vehicles, various settings are made by Nachlauf and Vorlauf geometry in order to match vehicle characteristics.

Small change in trail Vorlauf geometry

(1/1) Steering Axis Inclination

Description The axis around which the wheel rotates as it turns to the right or left is called the "steering axis". 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). This line is tilted inward as viewed from the front of the car an d is called "steering axis inclination"( S.A.I) or "kingpin angle". This angle is measured in degrees. Furthermore, the distance "L" from the intersection of the steering axis with the ground to the intersection of the wheel centerline with the ground is called the "offset", "kingpin offset" or "scrub radius".

Steering axis inclination Steering axis centerline

Wheel centerline

90

Offset L

(1/1)

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Wheel Alignment

Roles of Steering Axis Inclination 1. Reduction of steering effort

2. Reduction of kickback and pulling to one side

1. Reduction of steering effort Camber = zero Steering axis inclination = zero

1. Reduction of steering effort Since the wheel turns to the right or 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. This offset can be reduced in order to reduce the steering effort. Either of the following two methods can be used to make the offset small: (1) Give the tires positive camber (2) Incline the steering axis.

Large offset Steering axis inclination

Positive camber

Small offset

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2. Reduction of kickback and pulling to one side Large moment

Driving or braking force

Large offset

Wheel Alignment

2. Reduction of kick-back and pulling to one side If the offset is excessively large, the force due to driving or braking generates a moment around the steering axis whose magnitude is proportional to the amount of offset. Also, any road shock applied to a wheel will cause the steering wheel to jerk or kick-back. These phenomena can be improved by reducing the amount of offset. If there is a difference between the left and right steering axis inclination angles, the vehicle will typically pull to the side of the smaller angle (having the larger offset).

Small moment

Driving or braking force

Small offset

3. Improvement straight-line stability The steering axis inclination causes the wheels to automatically return to the straight-ahead position after the completion of turning. HINT: In front engine, front-wheel-drive cars, the offset is generally kept small (zero or negative) to prevent the transmission to the steering wheel of shock from the tires generated during braking or by striking an obstruction, and to minimize the moment created around the steering axis by the driving force at the time of quick starting or acceleration.

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Wheel Alignment

SERVICE HINT: If there is a difference between the steering angle on the left and right, there will also be a difference between the moments around the steering axis on the left and right during braking and the braking force will be greater on the side with the smaller s teering angle. Also, any difference between the left and right offsets generates a difference in the drive reaction force (torque steer) on the left and right. In either case, a force acts that attempts to turn the vehicle.

Small moment

Large moment Large angle small offset

Small angle large offset

(1/1)

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Wheel Alignment

Toe (Toe Angle, Toe-in and Toe-out)

Description

A Toe angle

Toe angle Front

B Toe-in : A < B Toe-out : A > B Role of toe angle No toe angle

Toe-in

Gravity (pull)

Gravity (pull)

Toe angle (toe-in and toe-out) Toe is the inclination of the wheel front and rear as seen from above the vehicle. The wheel installation angle is called the toe angle. When the front of the wheels are closer than the rear of the wheels, this is called "toe-in". The opposite arrangement is called "toe-out". Roll of toe angle Conventionally, the primary purpos e of toe angle has been to cancel out the camber thrust generated when camber is applied. Toe angle therefore prevented the front of the wheel from opening to the out side when toe-in was applied for positive camber. As a result of an increasing use of negative camber and improved performance of the tires and suspension in recent years, however, the need to cancel camber thrust has diminished. Thus, the primary purpose of toe angle has changed to ensuring straight-line stability. When a vehicle rides up on an incline on the road surface, the body tilts to one side. The vehicle feels as if it is about to turn in the direction in which t he body is tilted. If the front of each wheel is turned to the inside (toe-in), however, the vehicle will try to move in the direction opposite that in which the body is tilting. As a result, straight-line stability is maintained. SERVICE HINT: If toe-in is excessive, the side slip force causes uneven wear of the tires. If toe-out is excessive, it is difficult to secure straight-line stability. HINT: Side slip is the total distance that the left and right tires slip to the side while the vehicle is running. Both in the case of toe-in and negative camber, side slip occurs towards the outside. (1/1)

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Wheel Alignment

Turning Radius (Wheel Angle, Turning Angle)

Description

When the rotational angle of left and right wheels is the same (the knuckle arm is parallel to the vehicle centerline) Front

Side-slip

r 1

r 1 = r 2

r 2

L O1

O2

L Tie rod

Knuckle arm

When adjusting the rotational angle of left and right wheels (the knuckle arm inclined to the vehicle centerline)

r 1

r 2

r 2 r 1

L L

L L

L

L

L

O

L

The turning radius is the turning angle of the left and right front wheels during cornering. Giving the left and right different turning angles matches the centers of turning for all four wheels and increases the driving stability during cornering. For example, in the type of steering system in which the tie rods are located behind the spindles, if the left and right knuckle arms are mounted so as to be parallel with respect to the vehicle's center line, the left and right steering angles will be equal (α = β). Each wheel would turn around a different center (O1 and O2) even if they have the same radius (r1 = r2), so side slipping would be generated on one of the tires. However, if the knuckle arms are inclined with respect to the vehicle's center line, because the left and right wheels have different turning angles (α < β), they can be set to turn with different turning radii (r1 > r2) and around the same center (O), so the proper steering angle can be obtained. SERVICE HINT: If the turning radius is improper, the inside or outside tire slips sideways during cornering and smooth turning is not possible. This also generates uneven wear on the side slipping tire. (1/1)

Wheel Alignment Service Description

Frequent inspection and correction of wheel alignment are ordinarily not necessary under normal conditions of use. However, if the tires are worn un evenly, if steering is unstable, or if the suspension has had to be repaired due to an accident, the wheel alignment must be inspected and corrected. 1. General Wheel alignment covers several items such as camber, caster, steering axis inclination, etc., and each item is closely related to the other items. When inspecting and correcting, it is necessary to consider all items and how they relate to each other. 2. Where to measure and cautions concerning tester handling Recently a large number of new alignment tester models have come into use. However, note that the high-precision testers may be quite complex, and errors may oc cur without your being aware of it. Therefore, maintenance of the testers must be performed periodically to assure that they are always reliable. Always measure wheel the alignment with the vehicle parked on a flat, level area. This is necessary because, no matter how accurate the alignment tester is, correct values cannot be obtained if the place where the measurement are to be carried out is not level. 3. Necessity of inspection before measurement of wheel alignment Before measuring the wheel alignment, each factor that could affect the wheel alignment must be checked and necessary corrections made. Proper execution of this preparatory operation will give the correct values. Standard wheel alignment values are determined by the manufacturer with the vehicle in its "normal" condition. Therefore, when inspecting wheel alignment, it is necessary to have the vehicle as close to its normal condition as possible in which standard values are determined. (See Repair Manual for standard values.) Items to be checked before measurement of wheel alignment area. • Tire inflation pressure (under standard conditions) • Markedly uneven wearing of tires or difference in the sizes. • Tire runout (radial and face) • Ball joint play due to wear • Tie rod play due to wear • Front wheel bearing play due to wear

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• • • • •

Wheel Alignment

Lengths of left and right strut bars Difference between left and right wheelbase Deformation or wear of steering linkage parts Deformation or wear of parts related to front suspension Lateral body inclination (chassis ground clearance) (1/2) Description 4. Important of chasis-to-ground clearance adjustment before alignment adjustment

4. Importance of chassis-to-ground clearance adjustment before alignment measurement In a vehicle with independent front suspension, wheel alignment factors will vary depending upon the load because of changes in chassis-to-ground clearance. It is therefore necessary to specify the wheel alignment factors for the specified clearance. Unless otherwise specified, refer to the Repair Manual, etc. 5. Road test

Bounding *1

After adjusting the front axle, suspension, steering, and/or front wheel alignment, carry out following road test to check the result of the adjustments:

Toe

• Straight-ahead driving

(1) The steering wheel must be at the correct position + Camber

(2) The vehicle should run straight ahead on a flat road. (3) Excessive steering shimmy or flutter should not occur.

Caster Rebounding *2

*1 State in which shock absorbers is shortened *2 State in which shock absorbers is lengthened

• Turning The steering wheel should turn easily in either direction, and should return quickly and smoothly to the neutral position when released. • Braking The steering wheel should not pull to either side when the vehicle is broken on a flat, smooth road. • Checking for abnormal noise No abnormal noise must be heard during the driving test.

6. Measurement results and how to use them If the measured values deviate from the standard values, it makes the measured values within the standard values by adjusting adjustment mechanisms or replacing parts. (2/2)

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Wheel Alignment

Front Wheel Alignment Service

Toe-angle To adjust toe-in, change the lengths of the tie rod connecting the steering knuckle arms.

1. Tie rod behind the spindles A

A

Short

Long

B

B

1. In the type in which the tie rod is behind the spindles, increasing the tie rod length increases toe-in. In the type where the tie rod is in front of the spindles, increasing the tie rod length increases toe-out.

Steering rack housing Tie rod end

Steering rack end

2. Double tie rod type

A

2. In the double tie rod type, toe-in adjustment is carried out with the lengths of the left and right tie rod kept identical. If the lengths of the lef t and right tie rods are different, even correct toe-in adjustment will bring about incorrect turning angle adjustment.

B A = B

(1/1)

1. Separate camber adjustment

2. Separate caster adjustment

Camber and Caster Click on the bulb mark or the underlined sentence. The adjustment methods for camber and caster depend on the model. Below are typical methods. Since the toe-in changes if the camber and/or caster are adjusted, the toe-in must always be checked after the camber and/or caster adjustment.

3. Simultaneous camber and caster adjustment (1)

(2)

(3)

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Wheel Alignment

Steering knuckle movement

1. Separate camber adjustment On some models, the steering knuckle bolts can be replaced with camber adjusting bolts. Camber bolts have a smaller shank diameter allowing camber adjustment. This type of adjustment is used on strut type suspensions.

Shock absorber

Adjusting bolt

Lower arm

Front view

Strut bar bracket

Adjusting nut or spacer Strut bar

L

Lower arm

Movement of lower ball joint center when strut bar length is changed Top view

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2. Separate caster adjustment The caster is adjusted by changing the distance "L" between the lower arm and strut bar by using the nut or spacer of the strut bar. This type of adjustment is used on strut type or double wishbone type suspension, in which the strut bar is located in front of or behind the lower arm.


Wheel Alignment

3. Simultaneous camber and caster adjustment

(3)

(1) Movement of lower ball joint center when center of lower arm is shifted by turning of cam

Upper arm Lower arm Front shims

Rear shims

Top view

Upper arm shaft

Adjusting cam

Frame

Adjusting cam (2)

Movement of upper ball joint center when number of rear shims is increased or decreased

Lower arm

Movement of upper ball joint center when number of front shims is increased or decreased

Front

Movement of ball joint center when number of front and rear shims is increased or decreased simultaneously

(1) The eccentric cam type mounting bolt is at the inside end of the lower arm. Turning this bolt moves the center of the lower ball joint to incline and adjusts both the camber and caster. This adjustment method is used on strut type or double wishbone type suspensions. (2) Turning the eccentric cam type mounting bolts at the front and rear of the lower arm changes the installation angle of the lower arm and changes the position of the lower ball joint. This adjustment method is used on strut type or double wishbone type suspensions. (3) The upper arm mounting angle, that is, the upper ball joint position, is changed by increasing or decreasing the number and/or thickness of the shims. This adjustment method is used on double wishbone type suspensions. (1/1)

Standard values

Measure values

Left-right error

0° 20 45 ( 0.33 0.75 ) 30 (0.5 ) or less

+0 10 (+0.16 )

Left-right error

3 20 45 (3.33 0.75 ) 30 (0.5 ) or less

+4 20 (+4.33 )

Camber

Caster

Example of Camber and Caster Adjustment The following is an example of adjusting the Supra JZA80 (1998). (For details, refer to the Repair Manual.) (1) Measure the camber and caster.

Gauge

Alignment tester

(1/2)

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Front cam graduation (Longer)

r t e s C a ) ) ) ) ) ) ) ) ) 8 3 3 0 8 8 3 8 3 . 8 . 3 3 . 0 8 . 8 3 5 4 . 5 4 4 3 3 . 3 . 3 . 2 . ( ( 4 ( ( ( ( ( ( ( 8 ) 0 0 5 5 0 2 5 0 5 5 5 3 2 0 . ) 5 0 5 2 0 4 4 3 4 4 3 3 3 3 2 ( 3 3 2 . ) ( 0 8 2 0 2 . 2 ( 3 ) 5 . 8 0 2 ( 1 5 0 1 ’

’

’

’

’

’

’

’

Wheel Alignment

r t e 0 s a C 4 2 3 ) 3 4 . (

Camber

’

Caster

’

3

’

Camber 0 40’ ( 0.67 )

4

0 25’ ( 0.42 )

2

0 10’ ( 0.17 )

1

0 05’ ( 0.08 ) (Shorter)

3

-6

-5

-4

-3 -2

-1

’

’

0

1

0 20’ ( 0.33 )

2

3

4

5

Rear cam graduation (Longer)

-2

0 50’ ( 0.83 )

0 10’ ( 0.16 )

-3

1 05’ ( 1.08 )

-2

-1

0

1.8 Rear cam

2.2 Front cam Front cam : Rear cam :

-4

1 20’ ( 1.33 )

1

) -4 -3

(3) Adjust the front and/or rear adjusting cams according to the values read from the chart.

6

-1

0 35’ ( 0.58 )

2

Camber

(2) As shown in the chart, read the distance from the marked point to 0 point.

(Longer) 1.8 (Shorter) 2.2

(Shorter)

Front and rear cams

Front

Front cam

(Longer)

Front cam

(Shorter)

Rear cam

(Shorter)

(Longer)

Rear cam

(Longer)

(Shorter)

(2/2) Turning Radius (Wheel Angle, Turning Angle) The type with a knuckle stopper bolt can be adjusted, but the type without this bolt cannot be adjusted.

Knuckle stopper bolt

A

Tie rod end

B

Steering rack housing

HINT: In the case of rack-and-pinion steering gear, the wheel angle is typically determined by the point at which the steering rack end makes contact with the steering rack housing. Consequently, there is usually no knuckle bolt. If the lengths of the left and right tie rod ends are different, this can cause the wheel angle to be incorrect.

Steering rack end A = B

(1/1)

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Wheel Alignment

Rear Wheel Alignment

Description

Dual-link strut type

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.

Semi-trailing arm type

Outside

Suspension arm Outside Toe-out

Toe-in

Toe-in

Toe-out

Standard centerline Centerline

Double wishbone type Upper arm

No. 1 arm

Eccentric cams

Top view

No. 2 arm Toe angle change

Front view

Eccentric cam

Lower arm

Camber change

(1/1)

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Wheel Alignment

Exercise Use the Exercises to check your level of understanding for the material in this Chapter. After answering each Exercise, you can use the reference button to check the pages related to the current question. When you get a incorrect answer, please return to the text to review the material and find the correct answer. When all questions have been answered correctly, you can go to the next Chapter.

Chapter Page with Related Text

Exercises

All Answers Correct

Next Chapter Page with Related Text

Incorrect Answer

Return to page of related text for review

Exercises Incorrect Answer

Return to page of related text for review

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All Answers Correct


Wheel Alignment

Question- 1 The following illustrations show the wheel alignment. From the following word group, select the words that correspond to 1 to 4. 1.

2. 0

Front

Front

90

3.

4 0 Wheel centerline

90 90

a) Toe angle b) Caster and caster trail c) Steering axis inclination and offset d) Camber e) Turning radius

Answer: 1.

2.

3.

4.

Question- 2 The following statements pertain to the roles of the wheel alignment. From the following word group, select the words that correspond to 1 to 4. 1. Effects the linear stability and wheel recovery after turning.

2. Reduces the steering effort and reduces the kickback and pulling to one side.

3. The contact angle between the tire and road, as it affects cornering performance.

4. Makes the difference in the turning angle of the right and left wheels to improve turning performance.

a) Camber b) Caster and caster angle c) Toe angle d) Steering axis inclination e) Turning radius

Answer: 1.

2.

3.

4.

Question- 3 The following 1 to 4 below pertain to the inspection performed before wheel alignment measurement is conducted. Select the statement that is False. 1. Tire inflation pressure 2. Tie rod play due to wear 3. Steering wheel freeplay 4. Difference between left and right wheelbases

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Wheel Alignment

Question- 4 The following statements pertain to malfunctions caused by poor wheel alignment adjustment. From the following sentence group, select the sentence that correspond to 1 to 4. 1. Uneven tire wearing caused by side slip

2. Accelerated wearing of the inner facing side of the tire

3. The vehicle has become more easily affected by the shock from the brakes and road.

4. Accelerated wearing of the outer facing side of the tire

a) Camber is overly negative b) Camber is overly positive c) Caster is overly positive d) Offset is small e) Toe-in is excessive

Answer: 1.

2.

3.

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4.

Wheel_Alignment Handouts

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