With the improvement of road conditions, the driving speed of Land Ark electric cars is getting higher and higher, and now there are many high-end cars set up four-wheel alignment, which not only requires front wheel alignment, but also rear wheel alignment.
The reason is that for front-wheel drive electric cars and independent rear suspension electric cars, if the rear wheel alignment is not proper, even if the front wheel alignment is good, there will still be bad handling and early tire wear. In order to prevent the "radical rotation" and auto-steering phenomenon when driving at high speed, the structural design should ensure that the electric vehicle has understeering characteristics. The rear wheels of electric vehicles with a certain degree of camber and front beam can enable the rear wheels to obtain a suitable lateral deflection angle and improve the handling stability at high speed.
(1) Rear wheel camber
Like the front wheel camber, the rear wheel camber also has an effect on tire wear and maneuverability. The ideal state is the movement of all four wheels camber angle is zero, so that the tires and road contact well, so as to get the best traction performance and handling performance.
Wheel camber is not static, it varies with the up and down movement of the suspension. When the vehicle is loaded, the suspension sinks and causes the wheel camber to change.
With the improvement of road conditions, the driving speed of land ark electric vehicles is getting higher and higher, and now there are many high-grade cars set up four-wheel alignment, which not only requires front wheel alignment, but also requires rear wheel alignment.
The reason is that for front-wheel drive electric cars and independent rear suspension electric cars, if the rear wheel alignment is not proper, even if the front wheel alignment is good, there will still be bad handling and early tire wear. In order to prevent the "radical rotation" and auto-steering phenomenon when driving at high speed, the structural design should ensure that the electric vehicle has understeering characteristics. The rear wheels of electric vehicles with a certain degree of camber and front beam can enable the rear wheels to obtain a suitable lateral deflection angle and improve the handling stability at high speed.
(1) Rear wheel camber
Like the front wheel camber, the rear wheel camber also has an effect on tire wear and maneuverability. The ideal state is the movement of all four wheels camber angle is zero, so that the tires and road contact well, so as to get the best traction performance and handling performance.
Wheel camber is not static, it varies with the up and down movement of the suspension. When the vehicle is loaded, the suspension sinks and causes the wheel camber to change.
In order to compensate for the load, most vehicles with independent rear suspension often have a small positive rear wheel camber. Damage or misalignment of the slider barrels, bent slider bars, damage to the upper control arm bushings, bent upper control arms, spring compression or suspension overload can cause the rear wheel camber to have a tendency to become negative camber. Steering knuckle bending, lower control arm bending will make the rear wheel camber angle too large. Rear-wheel drive vehicles will become bent even with a rigid rear axle housing under excessive torque, severe overload or road damage.
(2) Rear wheel front beam
Like the front wheel front beam, the rear wheel front beam is also an important item in rear wheel alignment. If the front beam is improper, the rear tires will also be scuffed, in addition to causing steering instability and reducing braking efficiency. (For anti-lock braking system, remember this point). Like rear wheel camber, rear wheel front beam is not a static quantity. It has to change when the suspension shakes and bounces. Rolling resistance and engine torque also have an effect on it.
For front-drive vehicles: the front drive wheels should have a front beam and the rear driven wheels should have a negative front beam.
For rear-drive vehicles, the opposite is true: the front wheels should have a negative front beam, and the rear drive wheels of independent suspensions should be as front-bound as possible.
If the rear wheel front beam does not meet the technical requirements, it should affect the tire wear and steering stability, and its impact is the same as the front wheel front beam. The fact that the front beam measurement is within the specified range does not mean that the wheels must be correctly positioned, especially for the rear wheel front beam measurement.
This is especially true for rear wheel front beam measurements. If the front end of one rear wheel deflects inward by the same amount as the front end of the other rear wheel deflects outward, the vehicle will still run out of alignment because the rear wheels are not parallel to the longitudinal axis of the vehicle, even though the front beam value is within the specified range.
(3) Driving force action line
If the two rear wheels are parallel to each other and parallel to the whole vehicle, the driving force line will be perpendicular to the rear axle and coincide with the longitudinal axis of the vehicle. However, if the front end of one or both rear wheels is inward or outward, or one wheel is slightly retracted relative to the other, the drive line of action will deviate from the centerline, thus creating a drive deviation angle and causing the vehicle to deviate in the opposite direction of the deviation angle. For example, if the line of force is to the right, the car will run off to the left.
The presence of the drive force deviation angle makes the vehicle less stable in direction on icy, snowy or wet roads. It sometimes causes the vehicle to run off course when the vehicle is braking or accelerating sharply. The front wheels used for steering control have to overcome this effect on the rear wheels, thus increasing tire wear.
The only way to solve these problems is to eliminate the drive deflection angle. By resetting the front beam of the rear wheels, the drive line of action can be centered back. On most front-drive vehicles, this is easily done by using the factory-supplied front beam adjustment method, by placing front beam/wheel camber shims between the rear steering knuckle and the rear axle, or by using an eccentric shaft set. Because rear-wheel drive vehicles have an integral rear axle, rear wheel front beam adjustment is not as easy. Sometimes the underbody or beam position of the car is incorrect due to manufacturing or collision. If the chassis is not pulled on the collision repair to restore the control arm to the correct or restore the correct geometric characteristics of the elastic suspension, then the only way to correct it is by trying some kind of offset longitudinal arm bushings and mating coil springs or changing the position of the suspension lugs or leaf springs or U-bolts.
If the rear front beam is difficult to change, another best practice is to adjust the front wheel alignment based on the rear axle drive line rather than the vehicle longitudinal axis. By doing so, the steering wheel is not in the center position to eliminate the car runout phenomenon, but not the rear wheel tailing phenomenon.
