When the vehicle has been used for a long time, the user finds that the steering is heavy, shivering, running off, not straight, not returning, or the tire is worn unilaterally, wavy, lumpy and eccentric, and the car feels floating, bumping and swaying when the user is driving, he should consider checking the wheel alignment value to see if there is too much deviation and repair it in time.

front wheel alignment includes caster, caster, camber and toe-in. Rear wheel positioning includes wheel camber and toe-in one by one. In this way, front wheel positioning and rear wheel positioning are generally called wheel positioning, which is often called four-wheel positioning. The function of wheel alignment is to keep the car running stably in a straight line and steering lightly, and to reduce the wear of tires and steering parts when the car is driving.

caster angle of kingpin:

When the wheel is viewed from the side, the steering kingpin (the center of rotation when the wheel turns) leans backward, which is called caster angle. After the caster angle of the kingpin is set, the distance between the grounding point of the kingpin center line and the ground projection point of the wheel center (called the kingpin pitch, which is the same as the principle that the front wheel fork beam of the bicycle tilts backwards) is generated, so that the grounding point of the wheel is located at the rear end of the extension line of the steering kingpin, and the wheel is pulled backwards by the rolling resistance during driving, so that the direction of the wheel naturally faces the driving direction. Setting a large caster angle of the kingpin can improve the straight-line driving performance, and at the same time, the pitch of the kingpin also increases. Excessive pitch of the kingpin will make the steering wheel heavy, and the front and rear bumps of the wheels will be aggravated due to road surface interference.

kingpin inclination:

when the tire is viewed from the front-rear direction, the kingpin axis is inclined to the inside of the car body, and this angle is called kingpin inclination. When the wheel rotates around the kingpin, the lowest point of the wheel will fall below the road surface, but in fact, the lower edge of the wheel can't fall below the road surface, but the steering wheel and the whole front of the car will be lifted up by a corresponding height, so that the gravity of the car itself will restore the steering wheel to its original middle position, so the steering wheel can be easily reset.

in addition, the inclination angle of the kingpin also reduces the distance from the intersection of the kingpin axis and the road surface to the intersection of the center plane of the wheel and the ground, thus reducing the force that the driver puts on the steering wheel during steering, making steering easy and reducing the impact force transmitted from the steering wheel to the steering wheel. However, the inclination angle of the kingpin should not be too large, otherwise the tire wear will be accelerated.

camber of front wheel:

when the wheel is viewed from the front and rear direction, the tire is not installed vertically, but slightly tilted and opened in the shape of a figure of eight, which is called negative camber, while it is called positive camber when opened in the opposite direction. In the heyday of using diagonal tires, the camber angle was set to be relatively large because the tires were inclined to touch the ground to facilitate the operation of the steering wheel. Nowadays, cars generally set the camber angle very small, close to vertical. The flat radial tires used in automobiles are becoming more and more popular. Due to the characteristics of radial tires (high tread rigidity and wide tread), if the camber angle is set, the tire will be eccentric and the tire friction will be reduced. Due to the continuous use of power steering mechanism, the camber angle is also shrinking. Nevertheless, setting a little camber angle can exert appropriate lateral thrust on the wheel bearings on the axle.

toe-in:

the so-called "inner splayed foot" means that the left and right front wheels are inward respectively. The purpose of adopting this structure is to correct the outward rotation of the wheel caused by the camber angle of the front wheel. As mentioned earlier, steering wheel operation becomes easy due to camber. On the other hand, because the wheels are inclined, the left and right front wheels rotate outward respectively. In order to correct this problem, if the left and right wheels have inward angles, the positive and negative are zero, and the left and right wheels can keep moving in a straight line to reduce tire wear.

the above four positioning values are all indicators of front wheel positioning. The rear wheel alignment value is similar to the front wheel alignment value, but the rear wheel alignment of most cars is not adjustable.