Chassis measurements can only be carried out using an appropriate measuring system. Therefore, I limit myself here to a description of the main parameters determined during the measurement.
Wheel alignment and camber / transverse and longitudinal inclination of the kingpin
Wheel toe-in is the difference between the distances measured in front and behind the steered wheels at the height of their axis of rotation from the road. With positive wheel alignment, the distance between the wheels in front is less than the distance in the rear. With negative toe-in, on the contrary, the smaller distance between the wheels will be at the rear.
General positive convergence of wheels 0°5'± 10'.
The camber and lateral tilt of the kingpin reduce the transfer of shock loads from the road to the steering and keep the moment of friction of the wheels on the road when cornering to a minimum.
The camber is characterized by the angle of inclination of the plane of the front wheel relative to the vertical plane (the figure shows a positive camber with the wheel plane tilted at an angle α). BMW vehicles have negative camber.
The transverse inclination of the kingpin is characterized by the angle p between the axis of the kingpin and the vertical passing through the point of contact of the tire with the road, when viewed in the direction of the vehicle.
The camber angle of the wheels and the angle of the transverse inclination of the kingpin have a joint effect on the so-called running-in shoulder - the distance between the center of the bearing surface of the tire of the steered wheel and the point of intersection of the axis of the kingpin with the road. The greater the angle of the transverse inclination of the kingpin and the angle of camber, the smaller the running-in arm. Thanks to this, ease of steering is achieved and the impact of shock loads from the road surface on the steering rods is significantly reduced.
The longitudinal inclination of the kingpin is characterized by the angle between the axis of the kingpin and the vertical passing through the point of contact of the tire with the road, when viewed in a direction perpendicular to the direction of the vehicle. The longitudinal inclination of the kingpin has a proportional effect on the straightness of the movement of the front wheels. A slight longitudinal inclination of the kingpin causes a deviation from a straight-line movement on a bad road or with a side wind, and also forces the steering to not fully return to the neutral position after a turn.
Prerequisites for verification
- Steering in straight ahead position.
- The tire pressure corresponds to the prescribed value.
- Car in normal condition: 2 x 68 kg front, 1 x 68 kg rear middle, 1 x 21 kg in the center of the luggage compartment and a full fuel tank.
- Vehicle suspensions are preliminarily strongly elastically deformed.
- Steering is properly adjusted.
- No unacceptable clearances in the steering rods.
- No impermissible gaps in wheel suspensions.
- The draft of the car is correct.