On almost all sports cars, the front wheels are installed with negative camber; the only question is how much camber to set. Often fast cars are performed with more negative camber because it is supposed to help improve handling, especially when cornering. The negative camber provided by the front suspension improves the alignment of one wheel relative to the road. It could be the left front wheel in a right turn or right wheel in a left turn. This wheel carries a large dynamic load, so it is important to set the camber correctly to ensure correct position wheels are relatively expensive.
So, correct installation highly loaded front wheel is a very important task. As the main idea for installing a wheel, let's take an extreme case (unfortunately, found on some cars of early generations). We will consider the behavior of the right front wheel in a left turn. The suspension geometry provides positive camber front wheels up to 5÷7 degrees. When cornering at high speed, the tires look as if they want to come off the rims and the car clearly handles poorly. Suffice it to say that some changes in suspension geometry (increased longitudinal inclination steering axis to provide dynamic negative camber, increasing static negative camber, installing more hard springs suspension to reduce body roll, lowering the suspension height, changing the position of the suspension arms, etc. etc.) will lead to completely different behavior of the same car moving at the same speed in the same turn. The car can be made completely drivable, especially in comparison with the original version.
Many sports cars with large negative camber (up to 2.5÷3.5 degrees) do not always have good characteristics handling and have very rapid wear on the inner edge of the tire. Often such cars exhibit understeer. The reason lies in the fact that when too high angle camber of the front wheels, the contact patch of the tire with the road of the loaded wheel decreases the more, the more the wheel is turned. This effect is more pronounced on light vehicles with very wide tires.
Let's consider the behavior of a car under heavy braking. The front part of the car “dives” and additional negative camber almost always appears in the suspension. So, when braking, you need to have the maximum contact patch between the tire and the road. To provide maximum efficiency Braking wheels should be located as close to the vertical as possible, without any camber and toe (in practice this is never possible to implement).
It is believed that the most acceptable static negative camber should be within 0.5÷1.5 degrees. Avoid setting negative camber to more than 1.5 degrees.
Steering axis caster (Castor)
Wheel caster is defined as the angle between the vertical, restored from the point of contact of the wheel with the road, and the line connecting the centers of the ball joints steering knuckle(wheel hub). The longitudinal inclination of the steering axis leads to a change in wheel camber when turning the wheel to the left and right of the position rectilinear motion.
For example, when turning left, the right front wheel acquires additional negative camber while left wheel loses negative camber (movement towards positive camber). Both front wheels must have the same static steering angle. The greater the longitudinal inclination of the turning axis, the more the wheel camber will change when turning.
To improve the position of the wheels relative to the road when cornering, the caster angle of the steering axis can be changed. If the car has a large static negative camber (more than 2÷3 degrees), it is impossible to change the longitudinal inclination of the turning axis so as to further increase the negative camber in a turn (as you remember, we are talking only about the right front wheel in a left turn). In any case, the opposite wheel will lose negative camber, but very rarely you get zero camber and almost never positive camber. Basically, the inner wheel (in relation to the turn) does not change the camber as desired. Large static negative camber is usually installed where it is difficult to increase the caster of the steering axis to provide sufficient dynamic camber during heavy cornering.
When a vehicle's camber angle is set too negative for cornering, the outer edge of the tire rarely experiences noticeable wear, while the inner edge wears significantly. The tire wears out very quickly and almost always wears unevenly along the inner edge of both wheels.
Suspension adjustments that increase dynamic negative camber can result in understeer in sharp turns (understeer is less pronounced in long, shallow turns). It is necessary to do tuning work (of course, it is different on each car) in the area of adjusting the suspension characteristics, which will ensure best handling car.
It is believed that the most advantageous range of the longitudinal inclination of the steering axis is 3÷8 degrees. The initial installation angle of the longitudinal inclination should be equal to 3÷4 degrees, but it should be possible to adjust it in steps of 1 degree to the maximum (8 degrees) value. The caster angle is increased if positive camber of the outer (relative to the turn) wheel occurs when making heavy turns. For low-speed vehicles, the pitch angle should be within the range of 2÷7 degrees.
Steering axis inclination (KPI)
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1 - positive overhang (mounting plane (C) is between outside wheel and its plane of symmetry (D)), |
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Modern cars don't have a real king pin to turn around. steered wheel. However, the principle of a kingpin in the suspension still remains. The transverse inclination of the axis of rotation (king pin) is represented by a line connecting the centers of the ball joints. Corner lateral inclination is determined between this line and an axis perpendicular to the axis of rotation of the wheel.
A line passing through the centers of the hub hinges intersects the road surface at a certain point, more or less distant from the center of the contact patch. This distance (running shoulder) is quite an important indicator.
Typically, the intersection point lies inside the contact patch and the rims have a large positive offset. When changing the wheel track using spacers or using a disc special design, the situation is changing towards worsening the situation.
Note: the offset of the wheel rim is the distance between the plane of symmetry of the wheel and the plane of its mounting. There are positive and negative offsets. The offset is considered positive if the mounting plane is between the outer side of the wheel and the plane of its symmetry. With a negative offset, the mounting plane is located between the plane of symmetry of the wheel and its inner side. The term “offset” means the presence of a negative offset, and “in-set” means the presence of a positive offset, but we usually call both positive and negative offset by the term “offset,” which confuses the terminology. Further in the text we will indicate which one - positive or negative offset we mean.
The optimal angle of transverse inclination of the rotation axis lies in the range of 9÷12 degrees, it is preferable to set it equal to 10 degrees. It is usually not possible to change the caster angle, although its effective value can be changed (within certain limits) by installing appropriate negative camber.
IN mass production On cars, the wheels are installed with immersion inside the body (positive offset). In this case, they are guided by the main principle of creating a running shoulder: the intersection point of the wheel turning axis should be inside the contact patch of the wheel with the road and inside the wheel track. When building sports cars, wheels with a large negative offset are sometimes installed simply on the basis that “it looks better,” often without thinking about the harm done to handling.
Having a wide wheel track is good up to certain limits and certainly not at the expense of suspension geometry.
We will install disks with such a negative offset (or spacers of the appropriate thickness) so that the wheel moves away from the hub by 75 mm, thereby increasing the front wheel track by 150 mm. Due to innovations steering will tend to experience multiple kickbacks, especially on uneven surfaces. This situation is not very good and can result in loss of control of the car. This happens when the wheel hits a ledge. road surface and gets a tendency to turn in the direction of the resistance that has arisen (the left wheel wants to turn to the left, and the right wheel wants to turn to the right). This leads to the occurrence of a tipping moment relative to the position of the wheels and their axis of rotation.
The closer the intersection point of the transverse axis of rotation is located relative to the center of the contact patch (reduction of the running shoulder), the less the effect of the harmful overturning moment and vice versa.
Let's consider another case. Let a wheel with a large negative offset run over an uneven surface (for example, the left one). The other wheel (right) remains on flat surface. The car then tends to turn to the left.
Sometimes a suspension geometry similar to that of a go-kart (with a very large negative offset) is used. This results in the fact that when the wheel turns from the straight-ahead position, one side of the chassis is raised and the other is lowered. So, if the car turns left, the left front wheel tends to lift left side body, the right wheel tends to lower this side of the car. The more negative the offset, the more pronounced this tendency is (forced change in body geometry).
Many cars are equipped with wheels with a large negative offset, but only those cases in which this causes harm should be considered. If it is necessary to increase the vehicle track, then new suspension and steering arms should be made rather than installing spacers to increase the negative offset or wheel disks with increased negative offset. This is certainly a time-consuming but also the most effective way to get a well-driving car.
In accordance with the above, the point of intersection of the wheel's turning axis with the surface should at least pass along the inner edge of the tire, but the car's handling is better when this point lies in the center of the contact patch.
Avoid installing wheels with too much negative offset. Note that modern sports cars have wheels with a large positive offset.
The relationship between the longitudinal and transverse angles of inclination of the axis of rotation
These two geometric factors are closely related, since for a given steering angle, the front wheels change their camber when any of these factors changes. For example, if the car turns to the right, the left front wheel acquires additional negative camber, while the right wheel loses negative camber, sometimes even positive. In the opposite turn, the change in camber angles reverses direction. The behavior of the suspension can be monitored in stationary conditions: let someone rotate steering wheel, and you observe the change in the position of the wheels relative to the floor.
The combination of the longitudinal and transverse inclination angles of the steering axis can lead to the desired law of change in the dynamic camber of the wheels. For example, if a hub has 9 degrees of caster with 6 degrees of caster, the steering wheel angle will increase camber more than a combination of 12 degrees of caster and 3 degrees of caster. However, it is easier to adjust longitudinal inclination than transverse inclination.
The desired law for changing wheel camber at a given angle of transverse inclination of the turning axis can be obtained by adjusting only the longitudinal inclination. Once you understand the basic principles of suspension operation, your view of front suspension geometry will never remain constant: the more knowledge and experience you gain, the more interesting it will be to make changes to your suspension settings.
The relationship between the angles of the steering axis of the wheel will be influenced by body roll. The more body roll, the more the wheel camber changes in a completely unnecessary direction. Restoring balance can be directed: either install stiffer suspension springs or stabilizers lateral stability, or stiffer shock absorbers.
The dynamic relationship between changes in wheel angles, suspension angles, camber and body roll is very complex, so it is quite difficult to fully understand the operation of the suspension.
Chapter 5. Camber, longitudinal and transverse angle of inclination of the steering axis
Negative Camber
On almost all sports cars, the front wheels are installed with negative camber; the only question is how much camber to set. Often high-speed cars are designed with more negative camber because it is supposed to help improve handling, especially when cornering. The negative camber provided by the front suspension improves the alignment of one wheel relative to the road. This could be the left front wheel in a right turn or the right front wheel in a left turn. This wheel bears a large dynamic load, so it is important to set the camber correctly to ensure the correct alignment of the wheel relative to the road.
So, correct installation of a highly loaded front wheel is a very important task. As the main idea for installing a wheel, let's take an extreme case (unfortunately, found on some cars of early generations). We will consider the behavior of the right front wheel in a left turn. The suspension geometry provides positive camber of the front wheels up to 5÷7 degrees. When cornering at high speed, the tires look as if they want to come off the rims and the car clearly handles poorly. Suffice it to say that some changes in the suspension geometry (increasing the pitch of the steering axis to provide dynamic negative camber, increasing static negative camber, installing stiffer suspension springs to reduce body roll, reducing the suspension height, changing the position of the suspension arms, etc. and etc.) will lead to completely different behavior of the same car moving at the same speed in the same turn. The car can be made completely drivable, especially in comparison with the original version.
Many sports cars with large negative camber (up to 2.5÷3.5 degrees) do not always have good handling characteristics and have very rapid wear on the inner edge of the tire. Often such cars exhibit understeer. The reason is that if the camber angle of the front wheels is too large, the contact patch of the tire with the road of the loaded wheel decreases the more, the more the wheel is turned. This effect is more pronounced on light vehicles with very wide tires.
Let's consider the behavior of a car under heavy braking. The front part of the car “dives” and additional negative camber almost always appears in the suspension. So, when braking, you need to have the maximum contact patch between the tire and the road. To ensure maximum braking efficiency, the wheels should be located as close to the vertical as possible, without any camber or toe (in practice this is never possible).
It is believed that the most acceptable static negative camber should be within 0.5÷1.5 degrees. Avoid setting negative camber to more than 1.5 degrees.
Steering axis caster (Castor)
Wheel caster is defined as the angle between the vertical, restored from the point of contact of the wheel with the road, and the line connecting the centers of the ball joints of the steering knuckle (wheel hub). The longitudinal inclination of the steering axis leads to a change in the camber of the wheels when the wheel turns left and right from the position of straight-line motion.
For example, when turning left, the right front wheel gains additional negative camber while the left wheel loses negative camber (moving towards positive camber). Both front wheels must have the same static steering angle. The greater the longitudinal inclination of the turning axis, the more the wheel camber will change when turning.
To improve the position of the wheels relative to the road when cornering, the caster angle of the steering axis can be changed. If the car has a large static negative camber (more than 2÷3 degrees), it is impossible to change the longitudinal inclination of the turning axis so as to further increase the negative camber in a turn (as you remember, we are talking only about the right front wheel in a left turn). In any case, the opposite wheel will lose negative camber, but very rarely you get zero camber and almost never positive camber. Basically, the inner wheel (in relation to the turn) does not change the camber as desired. Large static negative camber is usually installed where it is difficult to increase the caster of the steering axis to provide sufficient dynamic camber during heavy cornering.
When a vehicle's camber angle is set too negative for cornering, the outer edge of the tire rarely experiences noticeable wear, while the inner edge wears significantly. The tire wears out very quickly and almost always wears unevenly along the inner edge of both wheels.
Suspension adjustments that increase dynamic negative camber can result in understeer in sharp turns (understeer is less pronounced in long, shallow turns). It is necessary to do tuning work (of course, it is different for each car) in the area of adjusting the suspension characteristics, which will ensure the best handling of the car.
It is believed that the most advantageous range of the longitudinal inclination of the steering axis is 3÷8 degrees. The initial installation angle of the longitudinal inclination should be equal to 3÷4 degrees, but it should be possible to adjust it in steps of 1 degree to the maximum (8 degrees) value. The caster angle is increased if positive camber of the outer (relative to the turn) wheel occurs when making heavy turns. For low-speed vehicles, the pitch angle should be within the range of 2÷7 degrees.
Steering axis inclination (KPI)
1 - positive offset (the mounting plane (C) is located between the outer side of the wheel and the plane of its symmetry (D)),
2 - negative offset (the mounting plane (C) is located between the plane of symmetry of the wheel (D) and its inner side.)
Modern cars do not have an actual kingpin around which the steered wheel turns. However, the principle of a kingpin in the suspension still remains. The transverse inclination of the axis of rotation (king pin) is represented by a line connecting the centers of the ball joints. The lateral inclination angle is determined between this line and the axis perpendicular to the axis of rotation of the wheel.
A line passing through the centers of the hub hinges intersects the road surface at a certain point, more or less distant from the center of the contact patch. This distance (running shoulder) is quite an important indicator.
Typically, the intersection point lies inside the contact patch and the rims have a large positive offset. When changing the wheel track using spacers or using a specially designed disc, the situation changes towards worsening the situation.
Note: the offset of the wheel rim is the distance between the plane of symmetry of the wheel and the plane of its mounting. There are positive and negative offsets. The offset is considered positive if the mounting plane is between the outer side of the wheel and the plane of its symmetry. With a negative offset, the mounting plane is located between the plane of symmetry of the wheel and its inner side. The term “offset” means the presence of a negative offset, and “in-set” means the presence of a positive offset, but we usually call both positive and negative offset by the term “offset,” which confuses the terminology. Further in the text we will indicate which one - positive or negative offset we mean.
The optimal angle of transverse inclination of the rotation axis lies in the range of 9÷12 degrees, it is preferable to set it equal to 10 degrees. It is usually not possible to change the caster angle, although its effective value can be changed (within certain limits) by installing appropriate negative camber.
In mass production of cars, wheels are installed with immersion inside the body (positive offset). In this case, they are guided by the main principle of creating a running shoulder: the intersection point of the wheel turning axis should be inside the contact patch of the wheel with the road and inside the wheel track. When building sports cars, wheels with a large negative offset are sometimes installed simply on the basis that “it looks better,” often without thinking about the harm done to handling.
Having a wide wheel track is good up to certain limits and certainly not at the expense of suspension geometry.
We will install disks with such a negative offset (or spacers of the appropriate thickness) so that the wheel moves away from the hub by 75 mm, thereby increasing the front wheel track by 150 mm. Due to the new features, the steering will tend to kick back a lot, especially on uneven surfaces. This situation is not very good and can result in loss of control of the car. This happens when a wheel hits a bump in the road surface and tends to turn in the direction of the resistance (the left wheel wants to turn left, and the right wheel wants to turn right). This leads to the occurrence of a tipping moment relative to the position of the wheels and their axis of rotation.
The closer the intersection point of the transverse axis of rotation is located relative to the center of the contact patch (reduction of the running shoulder), the less the effect of the harmful overturning moment and vice versa.
Let's consider another case. Let a wheel with a large negative offset run over an uneven surface (for example, the left one). The other wheel (right) remains on a flat surface. The car then tends to turn to the left.
Sometimes a suspension geometry similar to that of a go-kart (with a very large negative offset) is used. This results in the fact that when the wheel turns from the straight-ahead position, one side of the chassis is raised and the other is lowered. So, if the car turns left, the left front wheel tends to raise the left side of the body, the right wheel tends to lower this side of the car. The more negative the offset, the more pronounced this tendency is (forced change in body geometry).
Many cars are equipped with wheels with a large negative offset, but only those cases in which this causes harm should be considered. If it is necessary to increase the vehicle's track, then new suspension and steering arms should be made rather than installing spacers to increase the negative offset or wheels with an increased negative offset. This is certainly a time-consuming but also the most effective way to get a well-driving car.
In accordance with the above, the point of intersection of the wheel's turning axis with the surface should at least pass along the inner edge of the tire, but the car's handling is better when this point lies in the center of the contact patch.
Avoid installing wheels with too much negative offset. Note that modern sports cars have wheels with a large positive offset.
The relationship between the longitudinal and transverse angles of inclination of the axis of rotation
These two geometric factors are closely related, since for a given steering angle, the front wheels change their camber when any of these factors changes. For example, if the car turns to the right, the left front wheel acquires additional negative camber, while the right wheel loses negative camber, sometimes even positive. In the opposite turn, the change in camber angles reverses direction. The behavior of the suspension can be monitored in stationary conditions: let someone rotate the steering wheel, and you watch the change in the position of the wheels relative to the floor.
The combination of the longitudinal and transverse inclination angles of the steering axis can lead to the desired law of change in the dynamic camber of the wheels. For example, if a hub has 9 degrees of caster with 6 degrees of caster, the steering wheel angle will increase camber more than a combination of 12 degrees of caster and 3 degrees of caster. However, it is easier to adjust longitudinal inclination than transverse inclination.
The desired law for changing wheel camber at a given angle of transverse inclination of the turning axis can be obtained by adjusting only the longitudinal inclination. Once you understand the basic principles of suspension operation, your view of front suspension geometry will never remain constant: the more knowledge and experience you gain, the more interesting it will be to make changes to your suspension settings.
The relationship between the angles of the steering axis of the wheel will be influenced by body roll. The more body roll, the more the wheel camber changes in a completely unnecessary direction. Restoring the balance can be directed: either by installing stiffer suspension springs, or anti-roll bars, or stiffer shock absorbers.
The dynamic relationship between changes in wheel angles, suspension angles, camber and body roll is very complex, so it is quite difficult to fully understand the operation of the suspension.
Chapter 8. Brakes Chapter 9. Vehicle Settings Chapter 10. Testing and adjusting the vehicle
