In the original version of such a suspension, developed by MacPherson himself, the ball joint was located on the continuation of the axis of the shock absorber - thus, the axis of the shock absorber was also the axis of rotation of the wheel. Later, for example, on the Audi 80 and Volkswagen Passat of the first generations, the ball joint began to be shifted outward to the wheel, which made it possible to obtain smaller, and even negative values of the running-in shoulder.
Thus, run-in shoulder (Scrub Radius) is the distance in a straight line between the point at which the axis of rotation of the wheel intersects with the roadway and the center of the contact patch between the wheel and the road (when the vehicle is not loaded). When turning, the wheel "rolls" around the axis of its turn along this radius.
It can be zero, positive or negative (all three cases are shown in the illustration).
For decades, most vehicles have used relatively large positive roll-over leverage. This made it possible to reduce the effort on the steering wheel when parking compared to the zero shoulder of the break-in (because the wheel rolls when the steering wheel is turned, and not just turns on the spot) and frees up space in engine compartment due to the removal of the wheels "out".
However, over time, it became clear that the positive roll-over shoulder can be dangerous - for example, when the wheels of one side hit a curb section that has a different friction coefficient from the main road, the brakes on one side fail, one of the tires is punctured, or the steering wheel is out of adjustment out of hand." The same effect is observed with a large positive run-in shoulder and when driving through any bumps on the road, but the shoulder was still made small enough so that it remained unobtrusive during normal driving.
Starting from the seventies and eighties, as the speed of vehicles increased, and in particular with the spread of the MacPherson type suspension, which easily allows this with technical side, cars began to appear en masse with a zero or even a negative run-in shoulder. This allows you to minimize the dangerous effects described above.
For example, on the “classic” VAZ models, the run-in arm was large positive, on the Niva VAZ-2121, thanks to a more compact brake mechanism with a floating caliper, it was reduced to almost zero (24 mm), and on the front-wheel drive LADA Samara family, the run-in arm became narrower negative. Mercedes-Benz generally preferred to have a zero break-in shoulder on their rear wheel drive models.
The rolling shoulder is determined not only by the suspension design, but also by the parameters of the wheels. Therefore, when selecting non-factory "disks" (according to the terminology adopted in the technical literature, this part is called "wheel" and consists of the central part - disk and the outer, on which the tire sits - rims) for the vehicle, the manufacturer's specifications must be observed. valid parameters, especially the offset, since when installing wheels with an incorrectly selected offset, the rolling shoulder can change dramatically, which has a very significant effect on the vehicle's handling and safety, as well as on the durability of its parts.
For example, when installing wheels with zero or negative offset with a positive (for example, too wide) offset provided from the factory, the plane of rotation of the wheel shifts outward from the axis of rotation of the wheel that does not change at the same time, and the run-in shoulder may acquire an unnecessarily large positive value - the steering wheel begins to “tear out of hand” on every bump in the road, the effort on it when parking exceeds all permissible values (due to an increase in the lever arm compared to the standard departure), and wear wheel bearings and other suspension components increases significantly.
Why do we need camber, toe and caster angles?
Pendant without corners
If no corners are made at all, the wheel will remain perpendicular to the road during compression and rebound, in a constant and reliable contact with her. True, it is structurally quite difficult to combine the central plane of rotation of the wheel and the axis of its rotation (hereinafter we are talking about the classic two-lever suspension rear wheel drive car, for example "Zhiguli"), since both ball joints coupled with brake mechanism wheels do not fit inside. And if so, then the plane and the axis “diverge” by a distance A, called the rolling shoulder (when turning, the wheel rolls around the axis ab). In motion, the rolling resistance force of the non-driving wheel creates a tangible moment on this shoulder, which changes abruptly when driving through bumps. As a result, the steering wheel will constantly tear out of your hands.
In the transverse plane, the position of the wheel is characterized by the angles α (camber) and β (tilt axis)
In addition, muscle strength will have to overcome this very considerable moment in the turn. Therefore, positive (in this case) it is desirable to reduce the rolling shoulder, or even completely reduce it to zero. To do this, you can tilt the axis of rotation ab. It is important not to overdo it here, so that when going up, the wheel does not fall too much inward.
The rolling of an inclined wheel resembles the rolling of a cone
In practice, they do this: by slightly tilting the axis of rotation (β), the desired value is obtained by tilting the plane of rotation of the wheel (α). The angle of wasps is the collapse. At this angle, the wheel rests on the road. The tire in the contact zone is deformed.
It turns out that the car moves as if on two cones, tending to roll to the sides. To compensate for this trouble, the planes of rotation of the wheels must be brought together. The process is called convergence adjustment. Both parameters are tightly coupled. That is, if the camber angle is zero, there should be no convergence, negative - a divergence is required, otherwise the tires will “burn”. If the camber is set differently on the car, it will be pulled towards the wheel with a large slope.
With a positive run-in shoulder, turning the wheel is accompanied by lifting the front end of the body
The other two angles stabilize the steered wheels - in other words, make the car go straight with the steering wheel released. The angle of the transverse inclination of the axis of rotation (β) is responsible for the weight stabilization. It is easy to see that with this scheme (Fig.), at the moment the wheel deviates from the “neutral”, the front end begins to rise. And since it weighs a lot, when the steering wheel is released under the influence of gravity, the system tends to take its original position, corresponding to movement in a straight line. True, for this it is necessary to maintain the same, albeit small, but undesirable positive rolling shoulder.
Caster - pitch angle
Longitudinal angle tilt axis of rotation - caster - gives dynamic stabilization. Its principle is clear from the behavior of the piano wheel - in motion, it tends to be behind the leg, that is, to take the most stable position. To get the same effect in a car, the point of intersection of the pivot point with the road surface (c) must be ahead of the center of the wheel-road contact patch (d). To do this, the axis of rotation and tilt along ...
This is how caster works
Now when cornering, the lateral reactions of the road applied behind... (thanks to the caster!) try to put the wheel back in place.
Moreover, if the car is subjected to a lateral force that is not associated with a turn (for example, you are driving on a slope or with a crosswind), then the caster provides with an accidentally released steering wheel smooth turn machine "downhill" or "downwind" and prevents it from tipping over.
Positive (a) and negative (b) run-in shoulders
IN front wheel drive car with the MacPherson suspension, the situation is completely different. This design allows you to get a zero and even negative (Fig. b) rolling shoulder - after all, only the support of a single lever needs to be “pushed” inside the wheel. The angle of collapse (and, accordingly, convergence) is easy to minimize. So it is: the VAZs of the “eighth” family have a camber of 0 ° ± 30 ", toe-in of 0 ± 1 mm. Since the front wheels are now pulling the car, dynamic stabilization during acceleration is not required - the wheel no longer rolls behind the leg, but pulls it along. A small (1 ° 30 ") angle of longitudinal inclination of the axis of rotation is preserved for stability during braking. A significant contribution to the "correct" behavior of the car is made by the negative run-in shoulder - with increasing rolling resistance of the wheel, it automatically corrects the trajectory.
The angles for each car model are determined after a lot of testing, finishing work and re-testing. On an old, worn-out car, the elastic deformations of the suspension (primarily, rubber elements) are much greater than on a new one - the wheels diverge noticeably from much smaller forces. But it is worth stopping, as in statics all corners are again in their place. So adjusting a loose suspension is a waste of time. First you need to repair it.
You can nullify all the efforts of developers in other ways. For example, take a good bite back car. You look - the caster has changed its sign and the dynamic stabilization left memories. And if during acceleration the “sportsman” can still cope with the situation, then with emergency braking- hardly. And if you add non-standard tires and wheels with a different offset, then it is simply impossible to predict what will happen in the end.
The driver is driving a car. There is an obstacle ahead. It slows down, but the brakes "take" a little differently. In most cases, this difference is practically negligible. But at very hard braking(Fig. 1) the car throws to the side, maybe only half a meter, or skids and ... an accident. It often also occurs due to the fact that during braking the wheels of one side of the car were on ice, mud or water.
What do these cases have in common? The common thing is that the wheels of the right and left sides got into different conditions on the forces of resistance to movement. And, of course, these different conditions “provoked” a skid or a spontaneous turn of the car, which the driver did not always have time to correct in time.
"Self-defense" against skidding
All modern models necessarily have two independent circuits in the hydraulic brake drive (see). In order to guarantee that braking efficiency and, therefore, safety is maintained, it is necessary that at least one front wheel is braked in case of any malfunction. For this reason, the cheapest and simplest of the double-circuit - the diagonal scheme of the separate hydraulic drive brakes. But the transition to it forced the designers to put "self-defense measures" into the geometric ratios of the parameters of the front suspension and steering gear. This measure is the negative running-in shoulder.
A few words about the term itself. The running-in shoulder (Fig. 2) is the distance between point G of the tire’s contact with the road and point B. It denotes the intersection with the road of the continuation of an imaginary axis passing through the centers of the upper and lower ball joints of the double-lever front suspension. If the GV segment is located inside the vehicle track (Fig. 2a), it is considered positive. If, due to a certain combination of sizes of parts in the front suspension, the GV segment is outside the track, then the running-in shoulder r is considered negative (Fig. 2b).
Now let's see what happens when a car with a diagonal separate hydraulic brake circuit is braked. Suppose one of the contours (say, servicing the brakes front right and rear left wheels) is out of order. Pressing the pedal brakes the front left and rear right wheel(Fig. 3). At the points of their contact with the road, braking forces arise, Ftp and Ftz, respectively.
The moment from the force of inertia Fн, applied in the center of gravity of the car's CG on a shoulder equal to half the track, will turn the car around the front left wheel. It will only be neutralized to a small extent by the moment from the force Fтз, turning the car in the opposite direction around the braked rear right wheel. Let us separately consider the force Fтп. It is much larger than Ftz (due to the redistribution grip weight when braking), therefore, to simplify the scheme of action of forces, we will conditionally assume that only one front wheel, and the force of inertia turns the car around it. But approximately the same situation occurs in any scheme, and even if the drive is fully operational, but the wheels of one side of the car fall on a surface with a low coefficient of adhesion (icy, snowy, wet) during braking or in the event of a tire rupture on the move of one of the front wheels. Save while given direction very difficult and sometimes impossible. In addition, here the steered wheels tend to turn in the direction where the braking force can be realized through a higher friction coefficient, sharply increasing the turn of the car.
Let's turn to Fig. 4. When braking, the steered wheel rotates relative to the “pivot”, the imaginary axis AB, under the action of the braking force Ftp.
Effort on the steering wheel is reduced to almost zero
With a traditional, positive running-in arm (section GV in Fig. 4a), a moment Mt arises, acting in the same direction as the moment Mi, formed by the inertia force Fn on a shoulder equal to half the track.
If, however, the suspension of the front wheels is designed so that the running-in arm is negative (segment VG in Fig. 4b), then the product of this arm and the force Ftp applied at the point of contact Г of the wheel with the road will give the moment Mt, acting in the opposite direction to the moment Mi and will neutralize it.
During comparative tests of vehicles with negative and positive break-in shoulders, braking was carried out from an initial speed of 80 km/h in the absence of wheel lock and the steering wheel was released. One of the circuits of the diagonal drive circuit was artificially turned off. For the model with a positive running shoulder, the turning angle relative to the initial direction of motion was 140-160° with a significant lateral displacement. And the model with a negative running shoulder built into the design had a turn angle in the range of 15-17 °, that is, it practically did not deviate from the original trajectory. This is a clear evidence of the undoubted advantage of the negative break-in shoulder during asymmetric braking of the car.
Particularly interesting in this regard are the data obtained during tests on the amount of force or torque that the driver must apply to the steering wheel in order to keep the car on the desired trajectory when braking. The moment on the steering wheel required for this with a positive break-in shoulder reaches approximately 130 kgf * cm, that is, with a steering wheel radius of 20-25 cm, the driver must apply a force of more than 5-6 kgf. On a car with a negative break-in arm, the torque on the steering wheel under the same conditions is negligible and fluctuates around zero. At the same time, the adjustment of the trajectory of the steering wheel does not cause any difficulties for the driver.
Skid during braking - 10 times less
Such positive effect the negative running-in arm, which increases safety by maintaining a straight trajectory when braking or when the wheels of one side hit the slippery area roads.
And how big can the negative running-in shoulder be? Too large its value can lead to a deterioration in the stabilizing properties of the steering, which will have to be compensated for by an increase in the longitudinal inclination of the kingpin. But such "compensation", in turn, will increase the force on the steering wheel, which is undesirable. Therefore, for most cars, the value of the negative running-in shoulder ranges from 2 to 10 mm, reaching 18 mm in extreme cases (as done on the Audi-80). The other extreme is models with a running shoulder equal to zero ("Mercedes-Benz").
Proper wheel alignment is one of the critical factors, providing normal controllability, stability and stability of the car in a straight line and when cornering. Optimal suspension geometry parameters for each model are set at the design stage. The specified wheel alignment values are subject to change and require periodic adjustment due to natural wear and tear components and elements of the running gear or after suspension repair.
Assignment of wheel alignment angles
Correctly tuned suspension geometry allows the car to more effectively perceive the forces and moments that occur in the contact patch of the wheel with the road surface during different modes movement. This ensures predictable behavior of the car, namely: stability in a straight line, stability in turns, stabilization during acceleration and braking. Also, due to the absence of excessive rolling resistance of the wheels, more uniform tire wear occurs, which allows to increase their service life.
The wheel alignment values specified by the manufacturer are optimal for specific car and correspond to its purpose and suspension tuning features. However, if necessary, the possibility of their change or adjustment is structurally provided. The number of parameters that can be adjusted for each car is individual.
Types of basic car wheel alignment angles
| Parameter | vehicle axle | Adjustable parameter | What does it affect |
|---|---|---|---|
| Camber (camber) | Front rear | Yes (depending on vehicle) | Driving stability in a turn Premature wear tires |
| Toe Angle (Toe) | Front rear | Yes | Straight-line stability Premature tire wear |
| Roll Pivot (KPI) | Front | No | |
| Pitch Angle (Caster) | Front | Yes (depending on vehicle) | Vehicle stabilization while driving |
| Breaking shoulder | Front | No | Vehicle stability under braking Vehicle stabilization while driving |
Camber
wheel camber (English) camber) is the angle formed by the median plane of the wheel and the vertical passing through the point of intersection of the median plane of the wheel and the supporting surface. Distinguish between positive and negative camber:
- positive (+) - when the top of the wheel is tilted outward (away from the car body);
- negative (-) - when the top of the wheel is tilted inward (toward the car body).
positive and negative angles camber Structurally, the camber is formed by the position of the hub assembly and provides the maximum area of the tire contact patch with the road. In the case of a double lever independent suspension the position of the hub is determined by the top and bottom wishbones. In the formation of the camber angle is affected lower arm And suspension strut.
The deviation of the camber angle from the norm affects the car as follows.
- good stability car in corners;
- the grip of the wheels deteriorates during rectilinear movement;
- increased wear inside tires.
- good grip wheels with the road;
- stability in turns worsens;
- increased wear on the outer side of the tire.
wheel alignment
wheel alignment (English) toe) - the angle between the longitudinal axis of the car and the plane of rotation of the wheel. It can also be defined as the difference in distance between the front and rear sides of the wheel rims (in the figure this is the value A minus B). Thus, convergence can be measured in degrees or millimeters.
Car wheel alignment Distinguish between total and individual convergence. Individual convergence is calculated separately for each wheel. This is the deviation of the plane of its rotation from the longitudinal axis of symmetry of the car. The total toe-in is calculated as the sum of the individual toe-in angles of the left and right wheels of the same axle. Similarly, the total convergence in millimeters is determined. With a positive convergence (eng. toe-in) the wheels are mutually turned inward in the direction of travel, with a negative value (eng. toe-out) out.
Positive and negative wheel alignment The deviation of the values of the angle of convergence from the norm affect the car as follows.
Too big negative angle:
- increased tire wear on the inside;
- sharp reaction of the car to the steering.
Too large positive angle:
- maintaining the trajectory of movement worsens;
- increased tire wear on the outside.
The transverse angle of inclination of the axis of rotation of the wheel The transverse angle of inclination of the axis of rotation (eng. KPI) is the angle between the axis of rotation of the wheel and the perpendicular to the supporting surface. Thanks to this parameter, when the steered wheels are turned, the car body rises, as a result of which forces arise,
seeking to return the wheel to a straight position. Thus, KPI has a significant impact on the stability and stability of the vehicle in a straight line. The difference in the values of the angles of the transverse inclination of the right and left axles can lead to the withdrawal of the vehicle to the side with a large inclination. This effect can also manifest itself if the other wheel alignment angles correspond to the normal values.
Pitch Angle
Longitudinal angle of inclination of the axis of rotation Longitudinal angle of inclination of the axis of rotation (eng. caster - the angle between the axis of rotation of the wheel and the perpendicular to the supporting surface in the longitudinal plane of the vehicle. Distinguish between positive and negative angles of longitudinal inclination of the axis of rotation of the wheel.
A positive caster contributes to the emergence of additional dynamic stabilization of the car when driving at medium and high speed. As a result, the turning ability deteriorates. low speed.
Breaking shoulder
In addition to the above parameters, another characteristic is of great importance for the front axle - the running-in shoulder. This is the distance between the point formed by the intersection of the axis of symmetry of the wheel and the ground, and the point of intersection of the line of the transverse inclination of the axis of rotation and the ground. The run-in shoulder is positive if the point of intersection of the surface and the axis of rotation of the wheel lie to the right of the axis of symmetry of the wheel (zero shoulder), and negative if it is located to the left of it. If these points coincide, then the running-in shoulder is zero.
Breaking lever value This parameter affects the stability and steering of the wheel. The optimal value for modern cars is zero or positive run-in shoulder. The sign of the running-in shoulder is determined by the camber, the transverse inclination of the axis of rotation of the wheel and the offset of the rim.
Automakers do not recommend installing wheel disks with a non-standard departure, because this may result in changing the set running-in shoulder to a negative value. This can seriously affect the stability and handling of the vehicle.
Changing the values of the angles of installation of the wheels and their adjustment
Wheel alignment angles are subject to change due to natural wear of parts, as well as after replacement with new ones. Without exception, all steering rods and tips have threaded connection, which allows you to increase or decrease their length to adjust the values of the angles of convergence of the wheels. Convergence rear wheels, as well as the front ones, is adjustable on all types of suspensions, with the exception of the rear dependent beam or axle.
Mikhail's note, revealed some questions regarding the adjustment of the angles of the steered wheels.
Together, we'll try to figure it out.
collapse(camber)-- reflects the orientation of the wheel relative to the vertical and is defined as the angle between the vertical and the plane of rotation of the wheel.
F1 cars have negative camber
Convergence(TOE) - characterizes the orientation of the wheels relative to the longitudinal axis of the vehicle.
It is believed that the influence negative camber must be compensated by negative toe and vice versa, due to tire deformation in the contact patch, a “collapsed” wheel can be represented as the base of a cone.
The picture shows positive camber and positive convergence.
One of the benefits of negative toe is the increased speed of steering response.
In addition to the collapse and convergence, which can be seen with the "eye", there are several more parameters that affect the handling of the car.
Run-in shoulder— one of the parameters that affects the steering sensitivity. Thanks to him, the steering wheel "signals" a violation of the equality of longitudinal reactions on the steered wheels (surface unevenness, uneven distribution of braking forces between the right and left wheels).
Positive (a) and negative (6) run-in shoulder:
A, B - the centers of the ball joints of the front suspension;
B - the point of intersection of the conditional axis, "pivot", with the road surface;
D - the middle of the contact patch of the tire with the road.
The rolling shoulder does not affect the ease of steering. In the presence of a rolling shoulder, the longitudinal forces acting on the steered wheels create moments that tend to turn them around the axis of rotation. But in the case of equality of forces on both wheels, the moments turn out to be “mirror”, i.e. equal and opposite directions. Mutually compensating each other, they do not affect steering wheel. However, the moments load the details of the steering trapezium with tensile or compressive (depending on the location of the rolling arm) forces.
(Negative camber increases the positive value of the rolling shoulder)
Weight stabilization of the front wheels.
When the wheel is turned, the front of the car rises, therefore, under the influence of weight, the wheel tends to assume a position of rectilinear movement. Weight, or static, stabilization of the front wheels (i.e., ensuring their return to the direction of rectilinear movement) is provided by a positive rolling shoulder and a transverse tilt angle of the axis of the turntable.
Transverse tilt of the swivel stand.
SAI - the angle of the transverse inclination of the axis of rotation of the steering wheel (with a decrease in the transverse angle, the effectiveness of weight stabilization decreases, excessive tilt leads to excessive force on the steering wheel)
IA - included angle (an unchanged design parameter of the car, determines the mutual orientation of the axis of rotation and the wheel trunnion)
γ - wheel camber angle
r - run-in shoulder (in this case, positive)
rc - transverse displacement of the axis of rotation
In a 2-link suspension, the included angle is determined only by the geometry of the trunnion.
The mechanism of the weight stabilization.
When the wheel turns, its trunnion moves along an arc of a circle, the plane of which is perpendicular to the axis of rotation. If the axis is vertical, the trunnion moves horizontally. If the axis is tilted, the trajectory of the trunnion deviates from the horizontal.
The arc described by the trunnion has a vertex and descending sections. Position top point arc is determined by the direction of inclination of the axis of rotation of the wheel. With a transverse tilt, the top of the arc corresponds to the neutral position of the wheel. This means that when the wheel deviates from neutral in any direction, the trunnion (and with it the wheel) will tend to fall below the initial level. The wheel works like a jack - it lifts the part of the car above it. The “jack” is counteracted by a force that directly depends on a number of parameters: the weight of the raised part of the car, the angle of inclination of the axle, the magnitude of its lateral displacement and the angle of rotation of the wheel. She tries to return everything to its original, stable position, i.e. turn steering wheel to neutral
Dynamic stabilization of the front wheels.
To ensure the stability of movement, i.e., the desire of the car to move straight, it is not enough only the transverse tilt of the axis of the rotary wheel strut, especially on high speed. This is due to the appearance of additional rolling resistance and the gyroscopic effect, which can cause the influence of the wheel under the action of a disturbing force. For greater stability, a longitudinal inclination of the axis of the steering column of the wheel is introduced, due to which the point of intersection of the axis of rotation with the road surface is shifted forward relative to the contact of the tire with the road. Now the wheel tends to take a position behind the point of intersection of the wheel axis with the road, and the greater the rolling resistance, the greater moment returns the wheel to the straight-ahead position. With this displacement, the force acting on the wheel when turning also tends to straighten the wheel.
The main function of the caster is high-speed (or dynamic) stabilization of the steered wheels of the car. Stabilization in this case is the ability of the steered wheels to resist deviation from the neutral (corresponding to rectilinear motion) position and automatically return to it after the termination of the external forces that caused the deviation.
Steering wheel deflection can be caused by intentional changes in direction. In this case, the stabilizing effect assists at corner exit by automatically returning the wheels to neutral. But at the entrance to the turn and in its apex, the "driver", on the contrary, has to overcome the "resistance" of the wheels, applying a certain force to the steering wheel. The reactive force that occurs on the steering wheel creates what is called the information content of the steering.
The required reach of the axis of rotation (it is called the stabilization shoulder) is most often obtained due to its inclination in the longitudinal direction at an angle, which is called the caster. At low values of the caster, the stabilization arm turns out to be small in relation to the dimensions of the wheel, and the arm of the longitudinal forces (rolling resistance or traction) is completely miserable. Therefore, they are not able to stabilize the massive wheel. "Rubber comes to the rescue." At the moment of action of destabilizing lateral forces in the contact patch car wheel sufficiently powerful transverse (lateral) reactions are generated with the road, parrying the disturbance. They arise due to complex processes deformation of a tire rolling with side slip.
Additional information on side slip, the mechanism of side reaction and the stabilizing moment is given below.
As a result of wheel slip under the action of lateral force (power slip), the resultant of elementary side reactions always turns out to be shifted back in the direction of movement from the center of the contact area. That is, the stabilizing moment acts on the wheel even when the trace of the axis of rotation coincides with the center of the contact patch. The question arises: why do you need a caster at all? The fact is that the stabilizing moment (Mst) depends on various factors (tire design and pressure in it, wheel load, road grip, longitudinal forces, etc.) and is not always sufficient for optimal stabilization of the steered wheels. In this case, the stabilization arm is increased by the longitudinal inclination of the axis of rotation, i.e. positive caster. The destabilizing forces acting on the wheel of a moving car are caused by different reasons, but, as a rule, have the same inertial character. Accordingly, both lateral reactions and stabilizing moments increase with increasing speed. Therefore, the stabilization of the steered wheels, to which the caster makes a significant contribution, is called high-speed. With an increase in speed, it "steers" the behavior of the steered wheels. At low speeds, the influence of this mechanism becomes insignificant, weight stabilization works here, for which the tilt of the axis of rotation of the wheel in the transverse direction is responsible.
Setting the axis of rotation of the steering wheels with positive caster is useful not only for their stabilization. A positive caster eliminates the danger of a sudden change in trajectory.
Another favorable consequence of the longitudinal inclination of the axis of rotation leads to a significant change in the camber of the steered wheels when they turn.
The mechanism of dependence is easier to understand if we imagine a hypothetical situation when the axis of rotation of the wheel is horizontal (caster is 90°). In this case, the "turn" of the steered wheel is completely transformed into a change in its inclination relative to the roadway, i.e. collapse. The trend is that the camber of the outer wheel becomes more negative in a turn and the camber of the inner wheel becomes more positive. The larger the caster, the more change camber angles in a turn.
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Below is a printout of the settings of the F1 car, Lotus E20
Sources.
