Wheel alignment angles:
t is the angle of longitudinal inclination of the axis of rotation;
γ – camber angle;
δ is the angle of the transverse inclination of the axis of rotation;
M is the center of the wheel;
B-A - convergence of the front wheels;
A and B - distance (mm) between the wheels in front and behind;
δS - the angle of convergence of the front wheels;
S - track.
To ensure good stability and controllability of the car, the front wheels are set at certain angles relative to the body and suspension elements. Adjust three angles: the angle of the longitudinal inclination of the axis of rotation, the angle of collapse and the angle of convergence of the wheels. There is also the angle of the transverse inclination of the axis of rotation, but it is set by the geometry of the steering knuckle and is not adjustable.
Pitch angle - the angle between the vertical and the projection of the line passing through the centers of the ball bearings on a plane parallel to the longitudinal axis of the vehicle. It contributes to the stabilization of the steered wheels in the direction of rectilinear motion. This angle is adjusted by changing the number of shims on the upper arm axle mounting bolts. When removing washers from the rear bolt or adding them to the front bolt, it increases, and when rearranged, it decreases. Symptoms of deviation of the angle from the norm: car pulling to the side while driving, different efforts on the steering wheel in the left and right turns, one-sided wear of the tire tread.
Camber angle - the angle between the plane of rotation of the wheel in position «directly» and vertical. It contributes to the correct position of the rolling wheel during suspension operation. The angle is adjusted by changing the number of washers on the upper arm axle mounting bolts. To reduce camber, remove an equal number of washers from both bolts (packs of washers of equal thickness), to increase - add. At the factory, one washer 3 mm thick is put on each bolt, the rest of the washers are 0.75 mm. If necessary, remove thick washers. If all the washers are removed, but it is not possible to adjust the angles, check the condition of the rubber-metal hinges and the suspension cross member: the distance between the outer surfaces of the cross member brackets near the upper arm axle mounting bolts should be 736±1.5 mm. If this is not the case, replace the cross member, check the geometry of the body at the service station. With a strong deviation of the camber from the norm, the car can be pulled away from the rectilinear movement and one-sided wear of the tread.
Toe-in is the angle between the plane of rotation of the wheel and the longitudinal axis of the vehicle. Sometimes this angle is measured as the difference between distances A and B (see picture). Convergence contributes to the correct position of the steered wheels at various speeds and angles of rotation of the car. The angle is adjusted by changing the length of the lateral steering rods by rotating the adjusting sleeves with the tie rods loosened. Before adjusting the bipod of the steering mechanism is set to the middle position (steering wheel spokes are horizontal). Signs of abnormal toe-in: Severe sawtooth tire wear (even with small deviations), tire screeching in corners, increased fuel consumption due to high rolling resistance of the front wheels (car overrun is much less than expected).
The control and adjustment of the angles of installation of the front wheels is recommended to be carried out at a service station. The car is installed on a horizontal platform and loaded in accordance with the recommendations of the manufacturer. (Checking and adjusting the angles on an unladen vehicle is acceptable, but gives less accurate results.) Before doing this, you should make sure that the tire pressure is correct, the tread wear on the left and right wheels is approximately the same, there is no play in the bearings and steering, the rims are not deformed (radial runout - no more than 0.7 mm, axial - no more than 1 mm).
Checking the wheel alignment angles is mandatory if the suspension parts that affect these angles have been changed or repaired. First of all, the angle of the longitudinal inclination of the axis of rotation is checked and adjusted, then the camber angle, and lastly, the toe-in.
For a run-in car in running order and with a payload of 320 kgf (4 people in the cabin and 40 kgf of cargo in the trunk) wheel alignment angles must be within the following limits:
Pitch angle, t | 3°30'±30' |
Camber angle, γ | 0°30'±20' |
Front wheel toe-in, δS | (3±1) mm |
Changing the camber angles and longitudinal inclination of the axis of rotation when changing the number of washers with a thickness of 0.75 mm on the bolts of the upper arm axis:
Number of washers added or removed
|
Camber angle (γ)
|
Pitch Angle (t)
|
|
Front bolt
|
rear bolt
|
||
1
|
1
|
(8'42")
|
0
|
–1 –1
|
|
– (8'42")
|
0
|
1
|
0
|
– (7'30")
|
(20'24")
|
–1
|
0
|
(7'30")
|
– (20'24")
|
0
|
1
|
(15'18")
|
– (25'18")
|
0
|
–1
|
– (15'18")
|
(24'18")
|
–1
|
1
|
(27'30")
|
– (43'18")
|
1
|
–1
|
– (21'36")
|
(40')
|