Wheel alignment — general information

General information

1. The geometry of the suspension and its rigidity determine the possibility of limiting the vertical movements of the body and reducing its angular oscillations around the transverse and longitudinal axes. The front wheels turn around inclined axles, whose position is determined by the vehicle's suspension design.

2. Initial setting of chassis and suspension geometry is done at the factory. On modern vehicles, the initial settings practically do not change during operation and rarely require adjustment, however, when replacing worn or damaged suspension and steering components, they must be checked without fail.

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. It should be remembered that wheel alignment has a significant effect on vehicle stability, speed and tire wear patterns, as well as fuel consumption. The nominal values \u200b\u200bof the wheel alignment angles to be checked and adjusted for the vehicles considered in this Manual are given in Specifications at the beginning of the chapter.

4. Convergence (convergence) (see resist. illustration) called the angle between the lines formed when a horizontal plane cuts the following planes:

• The plane of symmetry of the car;
• The plane of the wheel.

Note: Toe-in can also be defined as the difference in distance between the extreme front and rear edges of the wheel assemblies (see ibid).

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. Normal convergence is usually less than a fraction of an inch (1 inch = 2.54 cm).

5. Collapse (see resist. illustration) called the angle between the lines formed when a vertical plane perpendicular to the plane of symmetry of the car is cut through the following planes:

• 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.

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 16.5). For all-wheel drive vehicles, this parameter characterizes the influence of traction forces and rolling resistance forces on the vehicle's handling.

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 16.5), 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. Coasting is the angle of the longitudinal inclination of the axis of rotation of the wheel, i.e., the angle between the vertical and the line formed when the plane of symmetry of the car intersects the plane perpendicular to it, drawn through the axis of rotation of the wheel (see illustration 16.5). 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, and also affects 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 16.5). The shoulder is considered negative when the last of the above points is between the center and the top 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 angle of the transverse inclination of the axis of rotation of the wheel is the angle of intersection of the vertical with the line formed at the intersection of the longitudinal plane drawn through the axis of rotation of the wheel, with the plane of the cross section of the car (see illustration 16.5). Along with the escape (see above) and the value of the longitudinal displacement of the axis of rotation (see ibid) affects steering sensitivity.

11. Another controlled parameter of the suspension geometry is the full angle of rotation of the vehicle's steered wheels. The nominal values of this parameter are determined separately for the inner to outer wheel and must be the same for both directions of rotation.

12. A general check of the suspension geometry is carried out on a special stand in a specialized workshop.

Conditions for checking wheel alignment

13. Checking the angles of the vehicle wheels requires a specially equipped overpass. Before starting the test, make sure that the following conditions are met:

• The air pressure in the tires corresponds to the nominal;
• The front wheels are mounted straight;
• The luggage compartment is not loaded, a load weighing 70 kg is laid on both front seats, the fuel tank is half filled;
• Elements of the car's suspension are upset with force (you can also roll the car forward and backward for 1 m);
• The steering gear is correctly adjusted;
• There are no backlashes in wheel bearings, tie rod ends and suspension ball joints;
• The tread depth of tires mounted on wheels of the same axle is the same.

14. To check the convergence and camber in «domestic» conditions, you can use templates specially made of thick cardboard, as mentioned in the relevant sections of this Chapter. Nevertheless, at the first opportunity, check the geometry of the installation of the wheels in a special workshop.