Caster angle is one of the most important parameters when tuning a car. The behavior of the car on the road depends on it. For ordinary car enthusiasts, it is not so important to set the exact angle; the presence of an electric power steering or power steering is enough for them.
For sports car racers the situation is different, you will have to rack your brains over this issue. There are many theories about how the caster adjustment angle affects how the car behaves. Sometimes it is very difficult to choose the optimal adjustment angle for the desired stability of your car.
What kind of caster should I install?
If the caster is adjustable, then, for example, in Samara, as already written, the maximum positive caster is 50 minutes. For other front-wheel drive vehicles, we recommend setting the caster as far into the plus range as possible, but only within the tolerances established by the automaker. Thanks to this, the car will improve directional stability at high speeds and the steering wheel will “self-stabilize” in a near-zero position. True, if there is a slight deviation from the basic tolerances (for Samara, for example, up to 10-15 minutes), then there will be no problems
Setting the caster to full zero (that is, vertically) will lead to the fact that the steering wheel, without power assistance, will seem a little heavy, and it will try with all its might to return to its original position. But you will only feel the discomfort for a few minutes until you get used to it.
Features of choosing a caster angle
Most often, the choice of angles depends on the “breaker” himself. This is not as good as it seems at first glance, since many of these specialists, with increasing experience, begin to be guided by the rules that they invented for themselves, and these rules quite rarely coincide with the theory. As a result, a car entrusted to one of these “Kulibins” deteriorates in handling, and the tires become unusable prematurely. Therefore, we recommend that you take a close look at the final angle readings and compare them with those recommended in the operating manual for a particular vehicle. If you notice an oversight, do not hesitate to point it out to the employee.
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And here is the car at the wheel alignment position. If you believe the printout, the installation angles almost fit into the norms, there are only small deviations. The master decided that it was these deviations that caused the withdrawal. Well, caster, for example: the right side differs from the left by almost half a degree! Without delaying the matter, he immediately suggested trying to change the suspension parts: what if something changes? And he explained, they say, the installation angles of a modern car are not adjustable, the car can only be repaired by replacing parts.
Garage answer
Artem did not hope for “suddenly”; instead, he went to an old friend, garage foreman Uncle Igor. He has his own wheel alignment stand, old, optical, but reliable. There were hopes for Uncle Igor, because the earth was full of rumors that he managed to solve problems that were too tough for the cool services.
Uncle Igor listened to a detailed story about how the ill-fated slip appeared, turned the printout in his hands and rendered a verdict: there was no madness, the car was working properly, and the culprit of the trouble was the “power heterogeneity” of the tire. To prove his words, he swapped the wheels on the front axle. And the car pulled in the other direction, to the left.
And they defeated the disease simply: they put the defective wheel back. The lead, of course, disappeared. And with it comes deja vu. Artem sighed with relief and went home happy. Although I didn’t have time to see my classmate.
Expert's comments
Regular participant of the “Behind the Wheel” WHEEL forum:
The force heterogeneity of a tire is a deviation from the norm in the dynamic properties of tires: the spread of radial and lateral forces, taper, lateral slip angle of the tire, radial and lateral runout, bulges on the sidewall. The factor least known to car enthusiasts is the force heterogeneity of the tire tread and sidewalls around its circumference (see Fig. 5 below) - individual sections of the tire with different hardness. (Behind the Wheel magazine previously wrote more about force heterogeneity.)
Preparation and procedure for adjusting wheel alignment angles of VAZ 2107
Having a level area, balanced equal-sized wheels and tires with the required pressure are far from the only requirements. It is equally important to remove the decorative caps before starting the adjustment and ensure:
- lack of free movement in “running” units;
- permissible play in the steering;
- proper tightening of all connections in the chassis;
- serviceability of the depreciation system.
It is advisable to check and adjust the chassis by first placing 70 kg on each seat and 40 kg in the trunk. However, adjustments can also be made on an empty car. With the steering wheel in the direction of straight-line motion, you should remove all the play in the suspension by shaking each of the four bumpers several times.
The geometry specified by the manufacturer should be installed according to a strictly defined relationship: castor-wheel-alignment.
Self-adjustment
Many car owners, trying to improve the driving performance of their cars, independently change the caster angle. As practice shows, this step is often justified, especially when it comes to domestic cars. It is not uncommon for a new VAZ car to have corners on the left and right that are very different from each other. Even if the discrepancy is within acceptable limits, controllability suffers greatly from this.
On rear-wheel drive Zhiguli cars, for example, VAZ-2105 or 2107, the angle is 3 degrees 30 minutes, plus or minus 30 minutes. On front-wheel drive models, for example, Priora, VAZ-2109, VAZ-2110, this angle is smaller, only 1 degree 30 minutes, plus or minus 30 minutes. If the caster of one front wheel of a VAZ-2105 is 3 degrees exactly, and the other is 4 degrees exactly, which is the norm by factory standards, the car will inevitably pull to the side.
Adjusting the caster angle is done by removing or adding washers on the suspension braces. The maximum number of washers allowed is two in the front and four in the rear, with the addition or removal of one shim changing the caster angle by 19 minutes. When adding washers, it is necessary to turn them over with their chamfers facing the thrust end of the stretcher.
Of course, this procedure cannot be carried out in a garage. Adjusting the caster angle is carried out only in conjunction with adjusting the camber and toe of the wheels, otherwise the suspension settings will be disrupted and the car may behave completely unpredictably.
To increase it, tuning enthusiasts remove the standard strut supports and install SS-20 supports instead. on front-wheel drive VAZ cars, including Priora, such a replacement, coupled with installing the maximum number of washers, allows you to increase the angle to 3 degrees. At the same time, the controllability of the car changes noticeably, the overall effect is positive.
Often, to improve handling, it is enough to simply replace the strut supports with the same ones. Despite the fact that the caster angle will not change significantly, the result will be, as they say, obvious. It's all about physical wear and tear. A signal that the supports need to be replaced is a low, thumping sound that occurs when driving on an uneven road at low speed. You can confirm the diagnosis by rocking the car and seeing if the struts dampen vibrations equally on the left and right sides. If not, you need to change the supports.
When choosing new strut supports, you should not choose the cheapest ones. It's better to buy either standard ones or SS-20. The latter are much more expensive, but they will also last much longer, and due to the fact that replacing supports is a complex and time-consuming task, the overpayment may be completely justified.
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What camber and toe angles should I set?
So regular or sports? The answer to what angles we will make is obvious - the correct ones. With this experiment, we only slightly lifted the veil of mystery that hides from the average rider the purpose and meaning of adjusting wheel alignment angles . It turns out that there are a lot of fairly simple and at the same time very effective ways to change the character of a car without resorting to expensive replacements of components and parts. The main thing is not to neglect adjustments that seem minor at first glance - they often turn out to be very important.
But which option should you prefer? I think the second one will be quite acceptable for most. It is the most logical for everyday driving, both with partial and full load. You just need to take into account that by increasing the longitudinal tilt of the rack, you not only improve the behavior of the car, but also increase the stabilizing (return) force on the steering wheel. So don't overdo it.
The last, “fastest” tuning option is more suitable for the near-sporting public who likes to improvise with the car. When giving preference to these adjustments, it must be taken into account that with increasing load, the values of the toe and camber angles will increase and may go beyond the permissible limits.
Pitch angle (caster) is the angle between the steering axis of the wheel and the vertical in a side view (Fig. 1). It is considered positive if the axis is tilted backward relative to the direction of movement.
Camber is the inclination of the wheel plane to the perpendicular restored to the plane of the road (Fig. 2). If the top of the wheel is tilted outward of the car, then the camber angle is positive, and if it is tilted inward, it is negative.
Toe is the angle between the longitudinal axis of the car and the plane passing through the center of the steering wheel tire (Fig. 3). Toe is considered positive if the planes of rotation of the wheels intersect in front of the car, and negative if, on the contrary, they intersect somewhere behind.
Frequent front suspension malfunctions
Maintenance and repair of the front suspension in Priora involves identifying the exact cause of the breakdown:
- If there is extraneous noise or a distinct thud is heard, the struts may need to be replaced. Check the tightness of the bolts securing the stabilizer hoses, tighten if necessary. If the cushions are worn out, replace them with new ones. If the supports at the top of the suspension strut are loosened to the body, tighten them. Assess the condition of the rubber component of the strut mount, ball joint, spring device, and compression motion buffer. If they are damaged or defective, replace them. Alternatively, check the wheels for imbalance.
- Liquid may leak from the strut, for one reason - the rod seal has worn out and collapsed. This will be indicated by the appearance of burrs on the rod, damage to the chrome surface, and mechanical defects in the sealing ring located on the strut body. Replace the old telescopic stand with a new one.
- If the suspension in the Priora breaks, you will have to replace the spring device and telescopic strut.
- It has become difficult to drive the car, it constantly skids to the side - it’s time to check the air pressure in the tires and normalize it. If the wheel alignment angles leave much to be desired, perform a wheel alignment. It may be necessary to replace the rubber lining in the suspension mounts or springs.
Read more: New fog lights on Priora
How the caster value is controlled
Like all angles, in geometry the caster angle is obtained by calculation or direct measurement using a special device.
Option one - direct measurement
It is difficult to name such a method as the most accurate. But it is simple and accessible for use in a garage. In the first option, it is necessary to manufacture and install special clamps with support pins at the measurement points. When installing clamps, it is necessary to ensure that the centers of the pins exactly coincide with the virtual line passing through:
- through the points – the centers of the ball joints of the upper and lower arms, in the case of a classic double-wishbone suspension;
- through the upper and lower mounting points of the shock absorber strut for McPherson;
- along the axis of the pivot in the longitudinal plane in a pivot suspension.
A thread or thin copper wire is stretched between the centers of the measuring pins. A thread with a plumb line is additionally suspended from the upper pin and a measuring device is attached - you can use a geodetic protractor. The beauty of this method of measurement is its simplicity and clarity, the downside is the simply monstrous measurement error, which allows you to see the magnitude of the angle with an accuracy of fractions of a degree.
Option two - measuring and calculating the caster value by the tangent of the angle
The measurement method already has a fairly high accuracy, but requires basic knowledge of geometry. As in the first case, it is necessary to install pins at the measurement points and tension the threads. To calculate the caster angle, we need to measure three distances as accurately as possible:
- L1 – the shortest distance along the thread stretched between the pins, through the attachment points of the ball joints or shock absorber strut, depending on the suspension design;
- Using a construction level indicator and a ruler, we measure the distance L2 - from the center of the lower measuring pin to the vertical thread with a plumb line. The measurement must be performed strictly according to the readings of the level indicator. Mark with a marker the point at which the ruler with the level indicator intersects the vertical thread with a plumb line;
- L3 – the distance along the length of the thread with a plumb line from the center of the upper measuring pin to the point you marked with a marker in step 2.
Further, by performing simple calculations using the formula tgA=L2/L3 or sinA=L3/L1, using the well-known table of Bradis values, you can obtain the exact caster value.
Option three – complex, requiring skills and knowledge
In the conditions of service stations or repair shops that service and repair car suspensions, a method is very often used in which the caster value is determined by calculation, measuring the wheel camber in two positions - the maximum turn to the left and to the right at the same specific angle.
Most measurements are performed using specialized stands and devices. With certain skills, you can measure the amount of camber using a ruler and a plumb line, but the accuracy of such measurements will not be higher than the previous option.
Mystery of action
In relation to the front suspension of a Russian front-wheel drive car, setting the angles usually begins with adjusting the caster. Actually, this parameter (caster), on the one hand, is intended to set the rest, and on the other hand, to some extent affects tire wear and other aspects related to the rolling of the car. In addition, this operation is especially complex - as I see it, this is precisely why it is “forgotten” on the assembly line. Only after this, having dealt with the longitudinal angles, does a competent specialist begin to adjust the camber, and subsequently the toe-in of the wheels.
Option 1
What is the caster responsible for and is it worth treating him so inattentively? The answers await us ahead, but for now we are puzzling the specialist with a request to bring the longitudinal inclination angles of the struts as far as possible to minus. Visually, we seem to be moving the front wheels back as much as possible, towards the mudguards of the wheel wells. This position of the wheels occurs quite often on used or old cars or after installing spacers that raise the rear of the car.
After the stand, the car moves much better than in its “factory” form, but still, something in its action cannot but excite. Individually, everything is good at first glance: the light steering wheel, quick responses to its minor deviations. And yet, you soon realize that “Samara” becomes overly angry and restless, which is especially obvious when the speedometer crosses the 80-90 km/h mark. It intimidates, so to speak, by the inconstancy of responses when entering a turn (not necessarily sharp). The car just wants to go somewhere unknown, requiring continuous steering from the driver. The situation becomes even more complicated when performing the “rearrangement” maneuver. And indeed, here it becomes obvious that it is better not to get into emergency conditions in its current form - it is unlikely that it will be possible to purely influence an emergency situation with the steering wheel. And indeed, having understood this, we again go to the regulating equipment.
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Option 2
At first glance, there are practically no serious interventions in the suspension - useless washers were simply removed, which prevented the wheels from taking the “correct” position (the struts were tilted to “plus”), the toe and camber angles were set to “zero”.
The fact that the trend of the VAZ-2114 has changed can be felt almost immediately by the steering wheel, which has become rigid and also excellently informative. Of course, the physical efforts have increased, but you quickly forget about them once you experience the actual character of the car. It’s as if an invisible hand is holding her back on the roadway, forcing her to drive not only intelligently, naturally, but also correctly. It is unknown where the instability, unclear connections and trajectory yaw went - the VAZ-2114 suddenly became a very comfortable car to drive, which was not without reason that Porsche professionals worked hard to fine-tune in their time.
Various maneuvers only strengthen our initial sensations: in the “rearrangement” the VAZ, as they say, went ahead, simply and naturally bypassing the previous version. To be honest, I don’t want to get involved in the discovered result—it’s so sufficient. But the circumstances of the test drive oblige.
Option 3
Not forgetting about , we allow you to “cripple” the camber by making it overly positive. Alas, it is not suitable to change it without adjusting the toe-in; therefore, we also do positive toe-in.
Indeed, at first glance, the changes in the operation of the car are not so strong. The steering wheel became lighter again, lazy responses appeared when entering a turn, and the lateral sway of the body increased. But there are practically no terrifying deteriorations in character - you adapt to aspects quite quickly. However, as soon as you go a little beyond the boundaries of what is permitted and create a state of emergency, the “cohesion” instantly disappears. With the occurrence of slips, it suddenly becomes difficult to get into the established corridor at the “rearrangement” and the car, which seemed submissive, suddenly gives up, even before the cherished borders. And the action in sharp turns does not look the best - the most powerful slipping of the front axle dominates.
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Option 4
With this option, you just need to remember your personal preferences for motorsport: “corners” - then we put in the right ones. Everything is negative everywhere, with the exception of the already pre-selected caster. And the VAZ-2114, as if infected with the excitement of research, from the first moments of communication longs to express its personal “I”.
It would seem that here it is - a sharp turn, which thirty minutes ago and at 80 km/h was scary to drive into. But now, after the last adjustment, the car allows you to enter a given turn even at 100-110 km/h, as if spurring on: “Come on, I have this opportunity!” Now it’s hard to restrain yourself from endless provocations; when an ordinary Zhigul suddenly rode like a prepared racing horse, causing a feeling of delight. Of course, the effort on the steering wheel has become very significant again, but in other respects it’s all five! The “rearrangement” maneuver only demonstrates this.
