Car Wheel Alignment Angles — General Information (BMW 7 Series E38)

Only the toe-in of the front wheels can be adjusted.

The geometry of the suspension and its rigidity determine the ability to limit vertical movements of the body and reduce angular oscillations around the transverse and longitudinal axes. The front wheels turn around inclined axes, whose position is determined by the hinges and suspension components of the vehicle. The most important are the following kinematic settings of the wheel assemblies in relation to steering and the transmission of forces between the tires and the road surface. Wheel alignment angles significantly affect vehicle stability, tire wear and fuel consumption. The nominal values of the wheel alignment angles subject to inspection and adjustment for the vehicles considered in this Manual are given in the Specifications at the beginning of Chapter Suspension and steering.

Convergence (convergence) is the projection onto the horizontal plane of the angle between the plane of symmetry of the vehicle and the plane of the wheel assembly passing through the center of the tire of the steering wheel; the difference in distances between the front and rear sides of the wheel rims can also be determined. Toe-in affects the straightness of the vehicle's movement and its controllability, and on front-wheel drive models it compensates for the resulting kinematic changes in the suspension geometry determined by the effect of traction force. At zero toe-in, the distance between the front edges of the wheels is equal to the distance between their rear edges.

Front wheel alignment

Collapse is the angle of the wheel in relation to the road surface in the vertical plane. If the upper part of the wheel is inclined to the axis of symmetry of the car, the camber is called negative, and vice versa. Correct adjustment of the camber determines the size and position of the contact patch of the treads with the road surface and allows to compensate for changes in the geometry of the suspension that occur during turns and when the car is moving on an uneven road surface.

Wheel alignment angles

Kinematic length of the journal is the shortest distance between the center of the steering wheel and its axis of rotation.

Shoulder the stabilization moment is the distance between the point of contact of the wheel and the point of intersection of its axis of 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.

Run-out it's called longitudinal tilt angle of the wheel pivot axis, i.e., the angle between the axis of rotation and the vertical in the side view. Together with the transverse inclination angle of the axis, the coasting affects the change in wheel camber when measuring the steering wheel angle, as well as the stabilizing moment.

Rolling 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. The shoulder is considered negative when the last of the above-mentioned points is between the center and the top of the wheel. The parameter affects the degree of impact of braking forces on the steering wheel and the magnitude of the stabilizing moment, and a negative shoulder of the rolling increases the latter.

Angle of transverse inclination of the wheel pivot axis is the angle between the axis of rotation of the wheel and the vertical in the plane of the vehicle's cross-section. Along with the coasting and the magnitude of the longitudinal displacement of the axis of rotation, it affects the sensitivity of the steering.

Conditions for checking wheel alignment angles

Checking the vehicle's installation angles requires a specially equipped overpass. Before starting the check, make sure that the following conditions are met:

• The air pressure in the tires corresponds to the nominal;
• The front wheels are mounted in a straight line;
• The car is not loaded, the fuel tank is full;
• The vehicle's suspension elements are forced down;
• The steering gear is adjusted correctly;
• Play in wheel bearings, tie rod ends and suspension ball joints is within acceptable limits;
• The tread depth of tires mounted on wheels of the same axle is the same.