Definition of chassis parameters (VW Passat B3)

Optimum driving dynamics and minimal wear can only be achieved with perfect wheel alignment. In the event of abnormal tyre wear, as well as unsatisfactory driving stability – poor stabilisation when driving straight ahead and poor steering qualities when turning – it is necessary to contact a workshop for an optical determination of the chassis parameters. The chassis can only be measured using a suitable measuring device. Therefore, we will limit ourselves here to a description of the main parameters determined during measurement.

Wheel alignment / kingpin camber and caster

The toe-in is the difference in distances measured in front and behind the steering wheels at the height of their axis of rotation from the road. As a rule, the front wheels should have a positive toe-in, since they - due to camber and rolling resistance - roll slightly outward when moving in a straight line, since there are minor gaps in the wheel hub bearings, suspensions and tie rod joints. Positive toe-in limits the tendency of the wheels to roll outward. With positive toe-in, the distance between the wheels in front is less than the distance in the back. With negative toe-in, on the contrary, the distance between the wheels will be less in the back.

In VW PASSAT cars, zero wheel alignment (0°) is installed. It is necessary to keep in mind that in cars with power steering, the alignment can only be adjusted on the right transverse steering rod.



Wheel camber and kingpin inclination reduce the transmission of shock loads from the road to the steering and maintain a minimum friction moment between the wheels and the road when turning.

Camber is the tilt of the front wheel plane relative to the vertical plane (the figure shows a positive camber with the wheel plane tilted at an angle of a). VW PASSAT cars have a negative camber angle. The prescribed camber angle is -1°20'±20'; with a 150 hp engine and a VR6 engine: -1°10±20': for vehicles designed for off-road driving: -1°±20'. The camber angle adjustment can only be made at the junction of the wheel hub bearing housing and the shock absorber strut,



The transverse inclination of the kingpin is characterized by the angle p between the kingpin axis and the vertical passing through the point of contact of the tire with the road, when looking in the direction of vehicle travel.

The camber angle and the kingpin angle have a combined effect on the so-called rolling shoulder - the distance between the center of the supporting surface of the tire of the steered wheel and the point of intersection of the kingpin axis with the road. The smaller the rolling shoulder, the easier the car is to control.


The jolts transmitted from the road to the steering also become significantly weaker.

The longitudinal inclination of the kingpin is characterized by the angle between the kingpin axis and the vertical line passing through the point of contact of the tire with the road, when viewed in a direction perpendicular to the direction of travel of the vehicle.

The longitudinal inclination of the kingpin has a proportional effect on the straightness of the front wheels. A slight longitudinal inclination of the kingpin causes a deviation from straight-line movement on a bad road or in a crosswind and also forces you not to completely return the steering to the neutral position after a turn.

Adjustment

To determine the chassis parameters, an inspection pit or lifting platform is required. The following prerequisites must be met for each parameter determination:

• The tire pressure is within the prescribed value,
• A perfectly flat horizontal surface for taking measurements.
• The car is unloaded.
• The car is pre-deformed strongly elastically.
• The steering is adjusted correctly.
• No unacceptable gaps in the steering gear.
• No unacceptable gaps in the wheel suspensions.