After a vehicle has been in use for a period of time, changes in vehicle positioning data may occur due to factors such as wear, repair, and replacement of chassis components.
Once the data change exceeds the specified range, the vehicle will inevitably experience abnormal driving. Such as abnormal tire wear, vehicle unable to drive normally in a straight line, and difficulty in aligning the steering wheel. These phenomena will lead to a sharp decline in the comfort and safety of vehicles.
"Four wheel positioning is so important that as auto repairers, we not only need to completely win in theory, but also conquer it in practice.".
Basic adjustment parameters for four-wheel alignment
The basic adjustment parameters for four-wheel alignment include front wheel toe-in, wheel camber, caster, and kingpin inclination.
Front wheel toe-in
Definition
The distance difference between the front end face and the rear end face of the front wheel (as shown in the following figure)
The normal front wheel toe-in value should be A>B
When A=B, it is zero toe in;
A> B, positive toe in;
When A<b, it="" is="" negative="" toe-in.<="" span="">
PS: The normal range of A-B should not be greater than 8mm.
Effect
1. Eliminate tire side slip caused by camber angle.
2. Enable the steering wheel to have the ability to automatically return to normal, ensuring that the vehicle travels in a straight line.
Effect of incorrect toe-in
1. The front toe is too large, causing severe wear on the outside of the tire.
2. The negative toe in is too large, causing severe wear on the inside of the tire.
3. Excessive toe in, zero toe in, and negative toe in can cause the wheels to roll and slip on the ground, increasing the driving resistance of the vehicle and tire wear, leading to poor vehicle handling and stability.
adjustment
Note: When adjusting the front wheel toe in, adjust the rear wheel toe in first.
Before adjusting, loosen the lock nuts on both ends of the steering rod ball heads and ensure that the steering wheel is in the center position.
Then adjust according to the data of the four wheel alignment instrument.
After adjustment, lock the lock nut tightly.
Adjusting the front wheel toe-in with a non four wheel aligner
This adjustment method is not recommended
1. Test drive to see if the direction deviates;
2. Visually check whether there is significant deviation between the two front wheels after the steering wheel is aligned;
3. Loosen the tie rod ball head lock nut;
4. Use chalk to mark the two front wheels (9 o'clock on the left and 3 o'clock on the right)
5. The distance between two marks measured by two people;
6. Push the vehicle so that the two marks are on the rear centerline (3 o'clock on the left and 9 o'clock on the right), and measure the distance between the two marks on the rear centerline;
7. Take the pull rod at the rear of the tire as an example: (opposite at the front)
The left pull rod needs to be loosened (lengthened) when pulling to the left, and the right side needs to be tightened (shortened) depending on the situation.
The left pull rod needs to be tightened (shortened) when pulling to the right, and the right side needs to be adjusted to see if it needs to be loosened (lengthened).
8. After the test run without deviation, tighten the tie rod ball head lock nut.
Camber angle
definition
The included angle between the wheel centerline and the vertical line.
When the center line of the wheel coincides with the vertical line, it is zero camber angle;
When the center line of the wheel is outside the vertical line, it is a positive camber angle;
When the center line of the wheel is inside the vertical line, it is a negative camber angle.
PS: A plumb line refers to a straight line downward by the gravity of a plumb bob, which can also be seen as a line perpendicular to the ground.
When a vehicle with a positive camber angle turns at high speed, the centrifugal force increases, and the vehicle body tilts outward, resulting in a greater positive camber angle.
When a vehicle with a negative camber angle turns, the camber angle decreases, and the vehicle's inclination decreases accordingly.
effect
1. Increase the safety of straight driving.
2. Reduce the load on the steering knuckle.
3. Prevent wheel slippage and optimize tire contact with the ground.
4. Prevent unnecessary camber due to load action.
5. Reduce the steering control force.
6. Improves stability during steering and ride comfort during driving.
Effect of incorrect camber angle
1. Excessive positive camber angle can cause directional drift and accelerate unilateral wear of tires.
2. The negative camber angle is too large, resulting in heavy steering and eccentric wear on the inner edge of the tire.
3. The camber angles on both sides are not equal, causing the vehicle to pull or roll.
Camber angle adjustment method:
The adjustment method varies depending on the vehicle model. The main adjustment methods include: adding or subtracting shims, adjusting the slots in the beam corners, adjusting the eccentric screws, adjusting the upper control arm, and adjusting the lower control arm.
Kingpin inclination angle
definition
The angle formed by the inclination of the kingpin axis inward in the transverse plane and the vertical line.
When the intersection point of the kingpin axis and the vertical line coincides with the intersection point of the wheel centerline and the ground plane, it is zero kingpin inclination angle;
When the intersection point of the kingpin axis and the vertical line is inside the intersection point of the wheel centerline and the ground surface, it is a positive kingpin inclination angle;
When the intersection point of the kingpin axis and the vertical line is outside the intersection point of the wheel centerline and the ground plane, it is a negative kingpin inclination angle.
effect
1. Reduce steering control force to make steering light.
2. Helps the steering wheel automatically return to normal.
3. If the offset caused by the kingpin inclination angle is negative, it can reduce the brake deviation phenomenon.
Effect of incorrect kingpin inclination angle
1. Too small, wheels do not return to alignment, and the vehicle yaw at low speeds.
2. Too large, strong correction effect, but difficult steering.
3. When the left and right sides are not equal, the vehicle tends to tilt.
Adjustment of kingpin inclination angle
Generally, the kingpin inclination angle cannot be adjusted. If the inclination angle error is too large, replace the steering knuckle.
Caster angle
definition
The angle formed by the inclination of the kingpin axis inward and backward in the longitudinal plane and the vertical line.
When the kingpin axis coincides with the vertical line, it is zero caster angle;
The kingpin axis has a negative caster angle in front of the vertical line;
The kingpin axis is a positive caster angle behind the plumb line.
Effect of caster angle
1. Improve straight line driving stability.
2. Ensure that the front wheels can automatically align after the vehicle turns.
Effect of incorrect caster angle
1. The caster angle of the kingpin is too small, which can easily cause the vehicle to yaw and cause high-speed shimmy.
2. The caster angle of the kingpin is too small, causing the front wheels to lose their ability to automatically return to normal after steering.
3. Excessive caster angle can make steering heavy.
4. Asymmetric caster angles between the left and right wheels can cause the vehicle to deviate to the smaller side.
Adjustment of caster angle of kingpin
Adjustment methods vary depending on the vehicle model. The main adjustment methods include: adding or subtracting shims, adjusting the slots in the beam corners, adjusting the eccentric screws, adjusting the upper control arm, and adjusting the lower control arm.
Note: If both the camber angle and the caster angle need to be adjusted at the same time, adjust the caster angle first and then adjust the camber angle.