Note. Only the convergence of the front wheels is subject to adjustment.
The suspension geometry 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.
The front wheels turn around inclined axles, whose position is determined by the hinges and suspension parts of the car.
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 \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.
Front wheel alignment
δ vs - 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
Convergence 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. The difference in distances between the front and rear sides of the wheel rims can also be determined.
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.
Wheel alignment angles
M - Wheel assembly center
r st — Kinematic trunnion length
n τ - Longitudinal displacement of the axis of rotation of the wheel
n — Positive stabilization arm
τ is the angle of the longitudinal inclination of the axis of rotation of the wheel
rs — Wheel axis lateral offset
r σ — Running arm
γ — Camber angle
σ — Angle of transverse inclination of the axis of rotation of the wheel
collapse called the angle between the lines formed by the section of a vertical plane perpendicular to the plane of symmetry of the car of 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.
Kinematic trunnion length represents the shortest distance between the center of the steered wheel and the axis of its rotation.
Shoulder stabilization called 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, which determines the magnitude of the stabilizing moment and affects the directional stability of the car and the distribution of forces in the steering when making turns.
coasting called the angle of the longitudinal inclination of the axis of rotation of the wheel, i.e., the angle between the axis of rotation and the vertical in the side view. Together with the lateral inclination angle of the axle, the coastdown affects the change in camber when measuring the steering angle, as well as the stabilizing moment.
Breaking shoulder is defined as the distance between the wheel's point of contact with the road surface and the point of intersection of its pivot axis with the road surface in the front view. 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.
The angle of the transverse inclination of the axis of rotation of the wheel represents the angle between the axis of rotation of the wheel and the vertical in the plane of the cross section of the vehicle. Along with the escape (and the magnitude of the longitudinal displacement of the axis of rotation affects the sensitivity of the steering.
Conditions for checking wheel alignment
Checking the installation angles of the car 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 car is not loaded, the fuel tank is full;
- Elements of the car's suspension are upset with force;
- The steering gear is correctly adjusted;
- Backlash in wheel bearings, tie rod ends and suspension ball joints do not go beyond the permissible limits;
- The tread depth of tires mounted on wheels of the same axle is the same.