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[YesAuto Technology] Friends who drive must be familiar with the term “four-wheel alignment”. A device that is slightly more complicated than a lift, a computer displaying weird positive and negative numbers, and a technician flipping over and over under the car, the so-called “positioning” is completed. Then, what is the so-called “four-wheel alignment”? What is set? Let's talk together and be a sensible person.

Simply put, “wheel alignment” is to accurately locate the relative position between the wheels and the steering knuckle and the frame or body through some parameters, so as to achieve a more ideal vehicle straight-line driving stability, steering convenience (steering wheels) and reduction. Wear of small tires and parts. The most ideal state is that when the vehicle is accelerating, braking, and turning, all four wheels can maintain the state of being perpendicular to the road surface, that is, maintaining the maximum contact area with the road surface.

After the vehicle leaves the factory, with the passage of time, the positioning parameters will change with the wear and impact of the parts. The “four-wheel positioning” we have done in 4S shops and various repair shops is a “correction” “Surgery”, by adjusting and restoring the original positioning parameters of the wheels to restore the original driving performance of the vehicle, just like “correction” can make our teeth more tidy.

For the front wheels responsible for vehicle steering, the positioning is more complicated. The positioning parameters include kingpin caster, kingpin inclination, wheel camber, and toe, while the positioning parameters of the rear wheels are mainly toe and camber. Below we will introduce the role of these parameters.

The kingpin tilts backward

Function: straight line stability, turning back to normal

Viewed from the side of the vehicle, the kingpin axis (the central axis of the wheel steering) is not completely perpendicular to the ground, but slightly inclined backwards. The angle between the kingpin axis and the vertical is the caster angle. The existence of the kingpin makes the wheels turn, the left and right sides of the tire tread and the tire sidewalls that are in contact with the road will be squeezed and deformed, generating a reverse force, causing the wheel to have a tendency to return to its own direction. The greater the caster angle, the better the driving stability of the wheels and the more obvious the return effect, but the correspondingly, the more laborious it is to turn the steering wheel when turning.

On most vehicles, the caster angle of the kingpin does not exceed 3°, but the caster angle of the kingpin varies with the vehicle's attitude and driving state, and is related to the travel of the suspension and the state of the wheels at the time. For example, when the vehicle is braked in an emergency, The caster angle of the kingpin may be close to zero or even negative. Therefore, many vehicles will find that the straight-line driving stability of the vehicle becomes worse (even with ABS) in the case of emergency braking when driving in a straight line.

★ The main pin is tilted inward

Function: stability, turning back to normal

Seen from the front (that is, in the horizontal plane), there is also a certain angle between the axis of the vehicle kingpin and the vertical, and the upper end is inclined inward. This is the inclination of the kingpin. The angle between the axis of the kingpin and the vertical is called Kingpin inclination angle.

Due to the inclination of the kingpin, the tendency of the wheels to turn is that the wheels move downward as a whole. However, since the pavement roads we drive on every day are hard pavements, the effect is: when turning, the wheels will resist Gravity lifts the front of the car, and when the steering force disappears, the wheels will automatically return to the right under the action of gravity. The greater the inclination angle of the kingpin, the more obvious this return effect is, but an excessively large angle will also cause excessive wear of the tire. This angle is usually between 5-8°.

King pin inclination and king pin inclination are also designed to provide normalizing force and driving stability, but the difference between the two is that the corrective force of king pin inclination has nothing to do with driving speed, while the role of king pin inclination is to return to normal. The higher the speed, the more obvious the effect. Therefore, when driving at high speed, the stability and return of the kingpin’s caster dominates, while at low speed, the role of the kingpin’s inward tilt plays a dominant role.

★ Wheel camber (negative camber)

Function: Enlarge the tire contact surface to offset the adverse effects

The wheel camber, as the name implies, means that the wheel tilts outward from the center line. The angle between the wheel rotation plane and the longitudinal vertical plane is the wheel camber angle.

If the vehicle keeps the wheels perpendicular to the road surface under no-load conditions, when a load is added or even fully loaded, the wheels will assume a “eight” “introverted” state due to the compression and deformation of the suspension stroke and the reduction in the clearance of the active surface. , So that tire wear increases, and a greater burden on the wheel hub bearings, in order to reduce this impact, people have designed a design-“wheel camber” this advance amount to offset the appearance of “inward tilt”, so that the vehicle is added After the load, the wheel can contact the road at a better angle, reducing the burden of eccentric wear and bearing. However, an excessively large camber angle will also cause the lateral eccentric wear of the tire to increase. The “tire gnawing” mentioned by many car owners is related to the unreasonable setting of the original wheel camber angle.

However, not all vehicles are designed with camber wheels. We have seen that many high-performance cars, racing cars and modified cars are set in the “bazi” state of “negative camber” (introversion), because high-performance vehicles More importantly, considering the effect of the centrifugal effect when the vehicle is cornering at high speed, when the wheel is driving at a high speed in a curve, the tire deforms due to the centrifugal effect and has a tendency to camber, so that only the outside of the tire can contact the road surface. Therefore, engineers use the initial “inward tilt” setting to offset this adverse effect, so that these high-performance vehicles can make more use of the middle or even the inner tread of the tire in the curve, increase the contact area, and improve the cornering. The limit.

★ Toe (front exhibition)

Function: to offset the adverse effects caused by wheel camber (inward tilt)

Although the wheel camber offsets some of the adverse effects of the vehicle when it is loaded, the design itself has drawbacks: the camber setting makes the wheels on both sides open outwards, unable to roll in parallel, and slip when driving, so we Only then has the “front beam”.

The distance between the front ends of the two front wheels is smaller than the rear end. This is the toe. The function of the toe is to offset the outward expansion of the wheels on both sides caused by the camber. Slip will also be offset by the slip caused by camber, so that the wheels can basically roll forward in parallel without slip. When the distance between the front end of the wheel is greater than the rear end, it is called negative toe, or forward span. This setting is to offset the adverse effects caused by the inclination of the wheel, and also for the wheel to roll forward in parallel.


We have introduced the meaning and function of the four-wheel alignment parameters of the vehicle here. Because the changes of these parameters will have a direct impact on the handling and stability of the vehicle, when your vehicle has problems with tire wear and driving stability , Need to consider whether the four-wheel alignment has been adjusted.

Under what circumstances need to do four-wheel alignment? Where to do four-wheel alignment? Please refer to the article on the car channel

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