What causes the vehicle's steering wheel to deviate?

If the steering wheel is not straight, but the vehicle can move forward normally when the direction is stabilized, it is likely that there is an assembly or adjustment problem. At this time, you can go to the service station to check whether there is a connection misalignment problem between the steering wheel and the steering gear. If it is just this problem, remove the steering wheel and re-align it.

There may be a second reason for the steering wheel to be out of alignment: deformation of the steering rod and clearance of the ball bushing. Because when the vehicle leaves the factory, the original engineer designs the four-wheel alignment value for it. If the steering rod, ball bushing and other components are operating normally, the vehicle will hardly have uneven tire wear or deviation (vehicle design problems are not excluded). What comes with it is that the steering wheel is not at the zero position and the driving is unstable. 

There may be a third reason for the steering wheel to be out of alignment, that is, the steering gear fastening bolts are loose. This situation often does not occur on new vehicles, but on trucks that have been in operation for more than 3 months. The steering gear has a service life according to the calibration of the entire vehicle, including its parts, and the service life is relatively long. However, if the truck driver vehicleries too much or too heavy cargo on the vehicle, the vehicle steering gear will be overloaded for a long time, and it is completely understandable that the fastening bolts are loose.

A misaligned steering wheel actually has a great impact on daily driving, especially for some drivers of tractor trucks. When reversing and unloading, if the steering wheel is not in the zero position, it is easy to misjudge the direction when reversing.

In addition to the above-mentioned misalignment caused by internal reasons of the steering wheel, inconsistent tire pressure on the left and right tires and differences in tire wear may also cause the steering wheel to not be in the zero position when the vehicle is driving. However, this situation is generally accompanied by vehicle yaw. 

Vehicle deviation means that the direction will automatically deviate with the driving speed during driving. If the truck steering wheel is not in the zero position, but the direction is kept stable during driving and the vehicle does not deviate, then it is most likely just a problem with the steering system assembly and no other components are involved.

Generally speaking, the deviation phenomenon includes the situation that the steering wheel is not at the zero point, but the deviation is not just a problem with the steering system. It is related to multiple links such as the chassis mechanism and the running mechanism.

First, let's take a look at the chassis system. 

The vertical axis is also called the kingpin, which belongs to the toe-in system of the truck. The kingpin is the axis around which the steering knuckle rotates around the steering axle (axis), also known as the steering axis. If its rearward tilt angle is too small, the vehicle will be unstable and the direction will deviate. 

How to change it in this case? In fact, it is very simple. This problem can be solved by increasing the kingpin caster angle. For trucks, the most direct way is to add a shim, which is what we often call a gasket. This problem can be solved by using shims of different angles and sizes in combination with four-wheel alignment. Its price is not expensive, but the disassembly and labor costs are high. 

Next, let's see if the driving force on both sides of the vehicle is balanced and stable. Taking an 8X4 four-axle vehicle as an example, if the force distribution on both sides of the drive shaft is uneven, one side has a bearing burnt and the driving force decreases, then the driving force on both sides may be unevenly distributed.

Another key point in the chassis system is the toe-in of the front wheels. The toe-in of the front wheels refers to the distance difference between the front and rear surfaces of the front wheels in the lateral direction of the vehicle, or the angle between the forward direction of the vehicle body and the plane of the front wheels. Simply put, all vehicles have a certain toe-in angle, which will also affect whether the vehicle can drive stably in a straight line. 

The toe-in of each model of vehicle is actually closely related to the four-wheel alignment. Different models of each brand have different toe-in values. After the truck turns back to the center position, it can automatically return to the straight-line driving position. This parameter is determined by the positioning parameters of the steering wheel, and toe-in is one of them. Whether the toe-in adjustment is reasonable has a lot to do with whether the steering wheel is worn and whether the vehicle will deviate.

Of course, in addition to the above reasons, there are other factors that can cause the vehicle to deviate, such as uneven loading of goods. For example, in the cargo compartment of a heavy truck, the right side is full of light goods and the left side is full of heavy goods. In this case, if there is a strong crosswind or a sharp right turn downhill, the vehicle may even roll over. 

The steering gear's self-centering angle deviation will also affect the vehicle's direction. Drivers can determine the steering gear's self-centering angle deviation by turning the steering wheel 90-180 degrees to the left and right and feel whether the weight of the steering wheel is evenly distributed. If there is significantly greater resistance when turning to one side, it can be determined that there is a problem with the steering gear itself.

At the same time, the tire pattern will also indirectly affect whether the vehicle will run off the track, such as the tire model, pattern, air pressure or wear on both sides are inconsistent. It is possible to run off the track under different road conditions, which is more common in the field of medium and heavy trucks.

Vehicle deviation is a relatively large problem in itself, which is not only related to the steering system, but also closely related to the chassis, running system and even tires and axles. At the same time, according to our understanding, some models may have problems with calibration when leaving the factory.

Apart from the manufacturer's design factors, most vehicle deviations are clearly related to the driver's driving habits, such as aging of parts caused by overloading and uneven cargo weight distribution.

Therefore, when our truck drivers find that the vehicle is offset or the steering wheel is not straight, they should provide the technicians at the service station with a detailed vehicle report. For example, when the problem occurred, the vehicle was driving on what road conditions, the tire pressure at the time, the load, and other key information. This can help the maintenance technicians find the relevant problems more quickly.