Off-road vehicle chassis rise is actually a systematic project, although the effective change is only to raise that few inches, but it affects more factors, the need for vehicle suspension, four-wheel positioning and other parts of the recalculation adjustment, today we will be the chassis rise on the vehicle has a large impact on several parts to talk about.
1. The angle that affects the swing arm and the camber of the wheel
A common approach to raising the chassis is to use longer shock springs and shock absorbers. However, the increased suspension will raise the angle of suspension, and we take the double wishbone suspension commonly used in off-road vehicles as an example (Figure 1) to simplify the suspension structure to the structure in the diagram (Figure 2), it can be clearly found that when the shock absorber is lengthened, the up swing arm and the hem arm will sag, and the tire will also show a tendency to indent inward, even if the wheel produces a positive camber angle (Figure 3).
Figure 1: Double wishbone suspension
Figure 2: Schematic of double wishbone suspension
Fig. 3: Wheel inclination and inclination of the mains
Here is a brief introduction to the wheel inclination, the general vehicle itself will be a setting of the wheel inclination when leaving the factory, generally using the negative camber angle setting. The main advantage of this is that when steering, affected by centrifugal force, the vehicle will have a tendency to dump in the opposite direction of the steering, and this trend will just offset the negative camber on the side of the direction after acting on the tire, so that the tire tends to fully adhere to the ground, resulting in greater grip. Simply put, the negative camber angle is set to make the vehicle have better adhesion when steering.
When the vehicle is raised, it will cause the wheel to have a positive tilt angle, which is not conducive to the vehicle's control on the road. But for independent suspension we can adjust the gasket between the upper arm shaft and the retention mechanism to adjust the angle of the inclination angle of the main pin, so that the wheel inclination is up to the angle we need.
2. Influence the angle of the universal joint
Due to the distance between the transfer box and the rear axle, the output position and the rear wheel differential are not in a horizontal straight line, so the front and rear of the drive shaft will be equipped with a gimbal joint, and after the chassis is lifted, it will also affect the vehicle transmission system.
The drive shaft of some off-road vehicles uses a sliding spline composed of a sliding fork and a spline shaft, which can be retracted within a certain range. This avoids the problem of shortening the wheelbase due to insufficient length of the drive shaft after the chassis is raised, at least in a certain range of rise, there is no need to replace the drive shaft or the drive shaft needs to be lengthened, but it is impossible to solve the gimbal angle caused by the chassis rise.
When the gimbal joint is parallel to the front and back joints, the universal joint is only subject to the torsional torque, and when the angle is generated at the current rear joint, the gimbal joint will be subject to multiple torques in each direction, and the larger the angle, the greater the moment of the gimbal joint, which will lead to the phenomenon of "jitter" when the vehicle starts, and even damage the gimbal joint when it is serious.
3. The putter needs to be lengthened
The structure of the thrust bar is actually very simple, that is, the red crossbar in the picture below, one end is connected to the axle, and the other end is connected to the body girder. The role of the putter is to suppress the lateral swing of the body compared to the axle, that is, to suppress the left and right swing of the vehicle.
However, it is clear that if the thrust rod direction shown in the figure below is used, when the shock absorber is compressed, the vehicle itself will be displaced to the right a small distance, and the same reason is that when the vehicle is elevated, the body will be displaced to the left (figure 4), affecting the vehicle's center of gravity.
Figure 4: Lateral displacement of the vehicle when the vehicle is elevated
However, as shown in the figure above, this displacement is very subtle, and the impact on the composition of the vehicle is not obvious, but it is more influential for larger and taller vehicles, requiring the replacement of the putting lever or the installation of a descending seat.
In fact, after the suspension is raised, it will directly change the parameters of the original vehicle suspension and four-wheel positioning, and these factory-tuned parameters usually represent the best value of the model in the comprehensive road conditions, and it is also the best value for the suspension parts to be used for a long time and the force within a reasonable range, which is also the reason why the modification factory has to bother to restore the parameters to the original factory settings after the parts are modified. It is also in order to restore the parameters, or to get as close as possible to the value of the original factory tuning, we need to replace many parts, and we need the so-called "pull a start to the whole body".