4.4.3 System operation principle 

4.4.3.1 Wheel alignment 

The driver turns the steering wheel to drive the vehicle in the desired direction. However, when running on the 
straight road, the driver shall keep the vehicle running straightly through continually operated the steering wheel 
of turn the vehicle through great force during turning a corner; thus, the driver shall consume great physical 
strength and suffers from great mental pressure.  In order to solve this problem as well as prevent the tires from 
being worn untimely, the wheels are installed on the body (or chassis) at a certain angle according to the certain 
requirements. These angles are summed up to be called as wheel alignment. Positioning refers to a comprehensive 
noun of the angle relationship among the front and rear axles, wheel, steering part and suspension part. 

If the wheel correctly positions, it is very easy to turn. During straight running, the driver only needs to regulate 
the steering wheel slightly to locate forward ahead and also turn with minimal intensity. In other words, it is very 
easy to turn if various angle relationships of forming wheel positioning are regulated correctly. However, even if 
one of the items is improperly adjusted, the following problems may be caused: difficult to steer, weak steering 
stability, bad steering returning and shortened service life of tire. 

There are such alignment angles as: toe-in, tire camber, main pin caster angle, main pin camber angle, steering 
angle, included angle, and thrust-angle, scrub radius, etc. 

The  above  angle  and  size  depends  on  the  suspension 

system, tire driving system (front engine front-wheel driving or front engine rear-wheel driving, two-wheel 
driving or four-wheel driving), and steering system (manual steering or power steering) used in the vehicle.Adjust 
these factors, so that the driving performance and the steering stability reach the best state. 

And can extend the 

service life of the parts. 

Commonly, the regulated angle is only recommended for the toe-in value during maintenance. 

1.  

toe-in 

. 

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The toe-in is used for measuring the distance of the wheel rotating forward or deviating from the center line of the 
vehicle.  Another comprehension to the toe-in is the contrast between the distance between the front of the two 
wheels and that between the rears of the same two wheels. If the vehicles are completely parallel, the two 
measured values should be equal and also the tie-on angle is zero. If the front of the wheel leans to the center line 
inward, the toe-in angle is positive.When the wheel is tilted outward, the toe-in angle is negative.The positive 
toe-in angle and the negative toe-in angle are also called as the toe-in of the front wheel and the toe-out of the 
front wheel commonly. 

Toe-in plays the role in compensating the trend that the tires roll inward or outward due to camber angle and road 
surface resistance, thereby ensuring the straightness of the vehicle. 

Forward 

Forward 

Back- 

ward 

Back- 

ward 

Front toe angle 

(wheel inward) 

Zero-toe-inangle 

(wheel inward 

parallel) 

Negative toe-in angle 

(wheel outward) 

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2. Camber 

angle 

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The camber angle is the inclination angle of the tire relative 

to 

the 

vehicle 

reference 

line. When the top of the 

wheel inclines outwards, the camber angle is positive at this time.When the topside of the wheel is tilted inward, 
the camber angle is negative at this time.The camber angle can be set to affect the control of the vehicle direction 
and the tire wear. 

Various suspensions and steering devices are designed to minimize the abrasion of the tire tread and transfer 
traction through maintaining the wheel to run perpendicular to the ground and straightly when starting the vehicle. 

An inappropriately set external camber angle will cause the tire to be excessively rapidly or unevenly worn; a too 
large positive camber angle will result in the wear of the side edge of the tire tread.When the load over the 
external side edge of the tire tread is higher than that over the internal side edge,such uneven wear will be resulted 
in. 

Overlarge negative camber angle may wear the inside of the tire tread.The load of the inside of the tire tread 
higher than that of the outside may cause uneven wear. 

3.    Kingpin caster angle 

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The kingpin caster angle is the one of inclining the kingpin axis forward or backward. 

The kingpin caster angle 

is obtained by the measurement of the angle between the steering axis and the perpendicular line when observing 
from the side. 

If tilted backward from the vertical line, it is called a positive kingpin caster angle; and if tilted forward, it is 
called a negative kingpin caster angle.  There is a point of intersection between the center line of the steering axis 
and the ground; the tire contacts with the ground with a center point; and the distance between the two points is 
called as kingpin caster shift. 

Vertical reference 

line 

Vertical reference 

line 

Positive camber

Vertical reference 

line 

Depression

Zero camber 

angle 

Negative 

camber

Embossing

Front

 

Kingpin caster angle

Kingpin rear inclined/moved distance

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The kingpin caster angle can produce the stability for straight running: if the vehicle has a positive kingpin caster 
angle, the left journal is to sink when the wheel turns left. (This is because bearing journal rotates around steering 
shaft, while this axle line is tilt) However, because fixed on the wheel assembly and can not move downward due 
to ground, the journal does not move downward as a matter of fact, but a left steering knuckle is forced to move 
upward.  It leads to the body to rise slightly; the steering is completed; the steering knuckle is forced to move 
downward due to the lifted body weight; thus, the journal returns to the original position to drive right ahead. 

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4.4.4 Diagnosis information and procedures 

4.4.4.1 Diagnosis descriptions 

Refer to 4.4.2 Description and operation, get familiar with the system functions and operation before starting 
system diagnosis, so that it will help to determine the correct diagnosis steps, more importantly, it will also help to 
determine whether the situation described by the customer is normal. 

4.4.4.2 Visual inspection 

1. 

Check whether there is after-sales optional device which will affect wheels and tires. 

2.  Inspect the easy to access system components to identify whether there is obviously damage or potential 

fault. 

3. 

Check if it exist conditions as follow: 

A.  Obvious tire and wheel run-out. 

B.  Check for obvious drive axle run-out. 

C. Incorrect 

tire 

pressure. 

D. Incorrect 

nosing 

height. 

E.  The wheel is bent or damaged. 

F.    Fragments exist on the tire or wheel. 

G.    The tire is abnormal or excessively worn. 

H.    Tire defects include tread deformation, separation or bulking caused by collision-slight side tire wall 

impression is normal and does not affect the travelling quality. 

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