Note: Only the toe-in of the front and rear wheels is subject to adjustment.
1. The geometry of the suspension and its rigidity determine the possibility of limiting the vertical movements of the body and reducing the angular vibrations around the transverse and longitudinal axes.
2. The front wheels turn around inclined axles, whose position is determined by the hinges and suspension parts of the car.
3. The most important are the kinematic settings of the wheel assemblies listed below in relation to steering and the transmission of forces between the tires and the road surface. Wheel alignment has a significant effect on vehicle stability, tire wear and fuel consumption. The nominal values of the wheel alignment angles to be checked and adjusted in the vehicles considered in this Manual are given in the Specifications at the beginning of the chapter.
4. Convergence (convergence) called the angle between the lines formed by the intersection of the horizontal plane of the planes of the wheel assemblies of one axle of the car; toe-in can also be defined as the difference in distance between the front and rear flanges of the wheel rims (see resist. illustration). Convergence affects the straightness of the vehicle and its handling, and on front-wheel drive models it compensates for the resulting kinematic changes in the geometry of the suspension, determined by the influence of the traction force. At zero convergence, the distance between the front edges of the wheels is equal to the distance between their rear edges.
18.4 Front wheel alignment
δVS Toe angle
a The distance between the front edges of the wheels
b Distance between the rear edges of the wheels
s Track
b - a Convergence
5. Collapse (see resist. illustration) called the angle between the lines formed by the intersection of the following three planes:
- a vertical plane drawn through the centers of the wheel assemblies of one vehicle axle;
- the plane of symmetry of the car;
- the plane of the wheel.
If the top of the wheel is inclined to the axis of symmetry of the car, the camber is called negative, and vice versa. The correct camber adjustment determines the size and position of the contact patch of the treads with the road surface and allows you to compensate for changes in suspension geometry that occur during cornering and when the car is moving on uneven road surfaces.
18.5 Wheel alignment
M Wheel assembly center
rst Kinematic stud length
nτ Longitudinal displacement of the axis of rotation of the wheel
n Positive stabilization arm
τ The angle of the longitudinal inclination of the axis of rotation of the wheel
rδ Lateral displacement of the axis of rotation of the wheel
rS Breaking shoulder
γ Camber angle
σ Tilt angle of the wheel axis
6. The kinematic length of the trunnion is the shortest distance between the center of the steered wheel and its axis of rotation (see illustration 18.5).
7. The stabilization arm is the distance between the point of contact of the wheel and the point of intersection of the axis of its rotation with the road surface in the side view (see illustration 18.5), which determines the value of the stabilizing moment and affects the directional stability of the car and the distribution of forces in the steering when making turns.
8. Caster angle of the wheel axis of rotation - the angle between the axis of rotation and the vertical in the side view (see illustration 18.5). Together with the angle of the transverse inclination of the axis (see below) the coastdown affects the change in camber when measuring the steering angle, as well as the stabilizing moment.
9. The break-in shoulder is defined as the distance between the point of contact of the wheel with the road surface and the point of intersection of its axis of rotation with the road surface in the front view (see illustration 18.5). The shoulder is considered negative when the last of the above points is between the center and the outer part of the wheel. The parameter affects the degree of influence of braking forces on the steering wheel and the magnitude of the stabilizing moment, moreover, the negative running-in arm increases the latter.
10. The lateral inclination of the wheel axis is the angle between the axis of rotation of the wheel and the vertical in the plane of the cross section of the vehicle (see illustration 18.5). Along with the escape (see above) and the value of the longitudinal displacement of the axis of rotation (see ibid) affects steering sensitivity.
Conditions for checking wheel alignment
11. Checking the angles of the vehicle wheels requires a specially equipped lift. Before starting the test, make sure that the following conditions are met:
- fuel, coolant and lubricants are full (if the tank is not full, compensate for the lack of weight by placing an appropriate weight on the rear center seat, assuming that half the tank corresponds to 24 kg);
- there should be no people and luggage in the cabin and luggage compartment;
- a set of on-board tools and a spare wheel are in place;
- the air pressure in the tires corresponds to the nominal;
- the tread depth of tires mounted on wheels of the same axle is the same and is at least 2 mm;
- runout and play of rims, hub assemblies, front suspension ball joints and tie rod ends are normal;
- the front wheels are set to the straight-ahead position;
- the steering column is set to the middle height adjustment position;
- the vehicle is level, i.e. the suspension has been shaken a few times.
12. During adjustment, both axles must be checked, otherwise the steering rack may be off-center. It is not necessary to check the wheel alignment angles when testing up to 2000 km, because. suspension springs may not settle yet.
13. Only camber and toe-in are subject to adjustment. The front wheel runout is not adjustable, but should be checked to determine the condition of the suspension.
14. It is necessary to check the wheel alignment angles in the following cases:
- automobile "does not hold the road";
- the car was involved in an accident;
- there is uneven wear of the wheel tread;
- have been removed / installed: steering gear, steering rod or its tip, any rear suspension arms, as well as (if the subframe was not fixed when removing): front suspension arm, front aluminum subframe console, front aluminum subframe and front stabilizer;
- the steering gear, tie rod or tie rod end, steering knuckle, aluminum subframe console, steel subframe, any rear suspension arms, rear suspension subframe or rear hub assembly have been replaced, and (if the subframe was not fixed during removal): front suspension arm rubber bushing and front stabilizer bar.
15. Checking / adjusting the angles of the wheels is carried out in the following order (proceed to the next item only after completing the current item):
- collapse of the front wheels;
- collapse of the rear wheels;
- convergence of the rear wheels;
- run-out of the front wheels;
- convergence of the front wheels.