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Car suspension

Everyone knows that contact and interaction with the road surface in dry and wet weather is different. And this impact is all the more noticeable the more often the car owner forgets about such a qualitatively important indicator as the wheel camber / alignment of the vehicle.

In order for the car to move straight, the wheels should stand naturally straight. It is clear to everyone. From our point of view – absolutely. What makes car suspension designers act against logic, turning out the wheels even at the production stage, ensuring their installation at different angles relative to the plane of symmetry of the car? If the wheels of your car have taken a wrong turn and you’ve been in a serious accident, call junk car removal mississauga.

It turns out that primitive logical constructions are true only when the car stands motionless, and even without passengers. As soon as you get behind the wheel, logic begins to burst at the seams, and if you take a couple of friends with you on the road, then from it (from logic, not from the company) literally no stone on a stone is left.

The reason is simple and complex at the same time. When the car is loaded, the elastic elements of the suspension sag under the action of the load. The body sags, rods and arms move, which is especially characteristic of independent suspension. All this leads to a change in the original orientation of the wheel plane in relation to the body and road surface. This is the effect of static, non-time-varying loads.

In dynamics, that is, in motion, everything is much more complicated. The frictional forces arising in the place of contact of the tire with the road come into play, tending to stretch the wheels of the car in different directions. This is where all the trouble for the suspension would end, if you and I were driving on a completely flat road, and only in a straight line, which, you must agree, is an absolutely far-fetched situation.

During maneuvering, the wheels experience even more complex impacts transmitted to the suspension and steering. For example, in order to take the load off the wheel hub bearings, the camber is changed, thereby increasing the service life of the bearings.

Trying to foresee and compensate for them in advance forces the wheels of the car to initially expose the position, which is determined by a large number of parameters and is called the wheel angles.

As a result, this contributes to improving the controllability and stability of the car, reduces stress on the elements of suspension and steering, reduces tire tread wear and fuel consumption.

The commonly used term “camber” is actually a much broader concept. Specialists distinguish more than a dozen basic and about the same number of auxiliary parameters that determine the installation of the wheels (usually in practice, they are subject to adjustment of a maximum of three values: camber, convergence, the longitudinal inclination of the rack). Usually they are measured in angular or linear values and have a strictly defined value for a particular make of car and suspension type.

Wheel alignment angles (WCA) are calculated theoretically during vehicle development and adjusted during development testing. The parameters of the RDC are provided and monitored during the assembly of the vehicle. And, as a rule, not only their absolute values are important, but also their difference for the left and right parts of the suspension.

Thus, the car leaves the assembly line fully prepared for high-speed maneuverable driving at a certain curb weight.

Thanks to the efforts of designers and manufacturers, the car’s suspension is adjusted as it should be. As they say, thank them very much, but what do we have to do with it? Those, who drive and those, who service cars? Why do we need to know all these tricks and subtleties of the suspension device?

The fact is that over time, the factory adjustments are violated. It occurs due to the natural wear of the suspension and steering components, accompanied by a change in the original dimensions and increased backlash in the joints. Therefore, the manufacturers recommend to diagnose the ATC every 30,000 km run and, if necessary, to adjust them.

A change in the originally set RCC may occur as a result of unforeseen circumstances: deformation of the upper and lower body in accidents, heavy bumps, when hitting a pit, a well, or a curb. Replacement of any parts of the suspension and steering during repair also violates the ATC.

In these cases, you should immediately diagnose the suspension geometry and adjust the wheel angles.

Symptoms that signal suspension geometry abnormalities include

Visually noticeable uneven wear of tire tread
abrupt change of position of a horizontal spoke of a steering wheel
noticeable effort on steering wheel while driving straight ahead or car’s drifting aside when releasing it
loss of directional stability when hitting an irregularity of the road
You may experience excessive noise from the tires as you drive

A frequent reason for violation of controllability and stability of the car is incorrect or inaccurate regulation of wheel alignment, or, simply speaking, violation of wheel camber and convergence. Below we will consider what wheel camber and convergence are, as well as how to adjust them.

So, you need to have the camber/convergence done. What do you need to do before your service visit?

The tires on the left and right should be the same size and be identical in model.
All four wheels must be exactly the same in all respects (seat diameter, width, offset). This condition is especially important for adjustments on computer test benches.
The parameters of the discs must correspond to the technical requirements of your car. Thus, for instance, it is undesirable to put on VAZ-08 (09) discs from “classics” and vice versa, as they have different offset, which leads to changes of wheel offset, assigned by suspension design. The same will be when using discs on Niva from Volga automobile and in general – discs with the offset less than regular.
If your wish to do camber / alignment is connected with installation of new set of tires, don’t hurry up to install tires until you properly check running gear and eliminate any failures. There are cases when the car owner, having “re-tuned”, comes to the wheel alignment, and the specialist finds some defect that doesn’t allow him to perform this operation. It’s good if this defect can be corrected on the spot, but sometimes the problem is of a more global nature, which does not allow you to fix it right away, because it requires a large financial outlay from the client. And he has to drive a certain amount of time on new tires without camber/alignment, which is sometimes disastrous for it.
Pay attention what position your car’s steering wheel takes when driving in a straight line and whether it has the same number of turns to the left and to the right of this position. Subsequently, focus the master’s attention on this information.

Align the tire pressure according to the instructions.
Of course, all of the above points should be tracked by a good camber master himself. But it is, as they say, on whom you will find yourself. Therefore, it is better to be reinsured.
So, you are already at the gate of car service. If you are here for the first time and none of your acquaintances have been here too, then the main task is not to run into a frank “pileup”. Some tips.
It would be nice to inquire if the service has a quality certificate for this type of service.
Find out what the scope of work included in the proposed rates. Till now, there are still “reserves”, where they limit themselves to camber and convergence, and about castor never heard of, not to mention displacement of front and rear axles, etc.
Carefully observe the process of checking and adjusting.

The camber adjustment process

Before starting the adjustment, an experienced technician should carefully inspect the car, make a diagnosis of the running gear, check the pressure in the wheels. If you find any deficiencies to inform the client and delay the performance of the CP to correct malfunctions.

A mandatory part of the preparatory operations is the operation of “run-out compensation of the wheel rim. Almost any wheel rim has geometric distortions. To exclude the influence of these distortions on the adjustment results, the operation of “compensation” is carried out. Externally, it looks like this: the front (or rear) axle of the car is suspended, instruments are placed on the wheels, and each instrument is individually adjusted for the wheel on which it is located. In principle, it is not necessary for an ordinary motorist to know these subtleties. But if you suddenly noticed that the master skipped this operation, it should alert you. The exception is the last generation stands (so-called 3D technology), where the “compensation” is made without axles swinging, and by rolling the car back and forth.

Next step: general diagnostics of the geometry of the chassis according to the instrument readings and identification of defects that may affect the stability and controllability of the vehicle regardless of the quality of camber/displacement adjustment (displacement of side members, displacement of axles, etc.).

The concept of camber/taxis includes not only the adjustment of camber and convergence, but also the measurement and if possible the adjustment of several other parameters, which I will discuss below.

Optics, Laser or Computer?

The client is always faced with the question, where to go: optical or computer test bench? Let me settle the eternal debate on this subject: it is possible to do SOMETHING BAD on both the former and the latter. In the end, everything depends on skill of the “leveler” and how much love he has for his equipment and in general – for his profession. The stand can be the coolest, but if it is not regularly checked and calibrated properly, all its accuracy comes to naught.

Optical testers are simpler, but more reliable in operation. True, measurement accuracy is an order of magnitude lower. A significant disadvantage of optical benches is that it can diagnose only one axis (front or rear) at a time. As a rule, only the “front end” is done, and we can’t see what’s going on with the rear axle. Meanwhile, the rear axle corner errors may affect the steering and stability of the vehicle several times more than the front axle. The optical bench does not show a very important parameter – rear axle rotation, which sets the so-called “driving angle” of the vehicle. Therefore, when adjusting on the optical bench, there is always a probability that the steering wheel will have some inclination when the car moves in a straight line.

The computer bench with closed loop measurement is free from this disadvantage. Besides, a competent specialist can easily identify all drawbacks in body geometry (whether the car was in an accident or not), since both axles are diagnosed simultaneously, their relative position in relation to car’s symmetry axis (rotation, displacement, etc.). But I should say at once: there are computer test benches with an open circuit of measurements and test benches of old years of release with imperfect programs. Their functionality is much lower than the previous ones. Therefore, you need to know where to go.

Another “plus” of the computer adjustment is in reception of the documentary printout of adjustment results. Another thing is that not everyone is able to understand what certain parameters printed there mean.

Camber is the angle of the wheel in relation to the pavement in the vertical plane (the angle “alpha” in the picture). If the top of the wheel is tilted toward the center of the car, the camber is negative, if outward, it is positive. In our case, the camber is: for the left wheel, +33 (minutes) for the right wheel, +36

Both values are in the tolerance field. Important! The left and right camber should be as close to each other as possible. The difference between them expresses the following parameter.

Difference in camber should not exceed 30, as it could cause the car to drift away from straight ahead.

Partial Toe – angle between the longitudinal axis of the car and the plane passing through the center of the left or right wheel separately.

Total Toe is obtained as a result of arithmetic addition of values of separate toe. In our case it is +15, which is within the tolerance range.

Caster is the angle between the wheel’s pivot axis and the vertical in the side view. Caster is a very important parameter. The difference in Caster values for the left and right wheels over the permissible values leads to drift of the car to the side of the wheel that has a smaller value. The difference in the car’s carriage angle is expressed by the following parameter.

The difference in wheel slope is the result of subtracting the smaller one from the bigger one and must not exceed 30
(in our case it is 7).

Transverse tilt of the steering axis (King-pin) – the angle of the wheel steering axis in the transverse plane when viewed from the front (angle “beta” in the first figure). It is set by designers for so-called weight stabilization of front wheels. On the Niva, this angle changes with the change of camber.

Displacement of front axle (Set-back) – characterizes the symmetric position of the front wheels relative to the axis of symmetry of the car. The front (rear) axle is a line drawn between the centers of rotation of the left and right wheels, respectively. Attention! It is a very important parameter! The closer the value of axle shift to zero, the better. The positive value of this parameter means that the left front wheel is slightly closer to the rear than to the right (in our case, +7, it is approximately 3.5 mm). At negative values – on the contrary. Therefore, this parameter characterizes the condition of body front (displacement of longitudinal members, bent suspension elements, etc.). Theoretically, the permissible deviation is 20…30. In practice – the less, the better.

Let’s pass to the rear axle. The following four parameters (separate toe-in, total toe-in, camber and difference of camber) are similar to front ones.

Angle of movement (Trust-angle) characterizes the rotation of the rear axle relative to the axis of symmetry of the vehicle. Attention! The important parameter! The closer to zero, the better. The positive value means rotation to the right, negative – to the left. “Zero” – the axle stands strictly perpendicular to the axis of symmetry of the vehicle. Maximum permissible values: up to 20 minutes (but it is undesirable, because even with these deviations the car goes as if a little sideways, even imperceptibly to the eye, which leads to bad behavior of the car on the road, especially slippery). Deviations more than admissible demand operative intervention (even on an unadjusted axle, it is necessary to find a way to level it).

Rear axle displacement (Set-back) – see front axle displacement (similar), but it is true only for cars with independent rear axle.

The most frequent failures, which appear after SR adjustment

The steering wheel is unsteady when driving straight ahead.

There are several reasons for this:

Increased steering clearance. The camber was performed without taking this into account and when driving, the free play is to the left or right, resulting in a slight tilt of the steering wheel.
The vehicle has a rotated rear axle. The camber/contraction was done on an optical bench (it doesn’t see or take this parameter into account), or on a computer bench, but with the vehicle angle measurement turned off.
Different tire pressure in the front or rear tires (the pressure equalization operation should have been performed by the technician before the camber adjustment).
There are hidden defects in the undercarriage, which for some reason were not detected during defectoscopy.
Sometimes there are cases when the steering wheel changes the angle of its position even when the front wheels are normally repositioned between each other.

Note: If you find the cause of the steering angle in addition to the tilt, you must first find and correct the cause of the steering angle and then look at the true position of the steering wheel.

The vehicle is pitching sideways in a straight line.

Check the effect of the front tires on the steering, even though you have new tires. Swap the left and right front wheels. If the steering goes to the opposite side, it is the tire. Run your wheels in a circle and look for a pair, which will make the car go straight. This cause of yaw is very common lately. The quality of manufacturing is to be blamed. As experts say – it is so-called power inhomogeneity of tire frame.
Only the front axle of the car was diagnosed while making the camber/contraction. You need to diagnose the rear axle. It may be the cause (bent, deformed, misaligned, etc.).
There are hidden defects of running gear, which were not detected during defectoscopy.
Poorly executed SR. Request redo.
The car wasn’t driving before SR adjustment, but there was rubber wear, after SR the drift appeared

The cause is most likely in the tires (see point above). The car was running smoothly before, because the drift created by the rubber was counterbalanced by the drift to the opposite side, created by wrong SR. If we eliminate one cause of the drift (in our case, SR), the second one remains – the drift appears.

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