BMW 7 Series: General Information And Definitions

Toe angle difference

a - Toe difference angle

D - Centre point of operating circle

The toe angle difference is the angle adjustment of the inner cornering wheel relative to the outer cornering wheel when negotiating a curve. Steering is designed in such a way that angular position of wheels changes as steering lock progresses.

A correctly adjusted toe angle difference produces equal values for left and right lock with consideration of factory tolerances.

Fig. 11: Identifying Toe Difference Angle From Centre Point Of Operating Circle

Toe angle difference provides information on corresponding operation of steering trapezoid for left or right steering lock from center position.

Camber

Inclination of the wheel from the perpendicular.

Fig. 12: Identifying Camber (Inclination Of Wheel From Perpendicular)

Toe

Reduction in distance of front of front wheels to rear of front wheels. The toe-in prevents the wheels from moving apart during driving and thus:

• the wheels from vibrating and grinding
• excessive tire wear
• excessive strain on the steering linkage and its links/joints
• heavy vehicle steering

Measurement is performed in "straight-ahead mode".

Fig. 13: Identifying Toe-In

Castor

Is the inclination of the kingpin in the direction of travel viewed from the side. The line through the center point of the spring strut support bearing and the control arm ball joint corresponds to the "kingpin".

Thanks to caster, wheels are pulled and not pushed. In a similar manner to king pin inclination, when driving in curves or around corners, returning forces are reproduced to help return wheels to straight-ahead position.

Fig. 14: Identifying Caster

Geometrical driving axis 1

Is the angle bisector from the total rear-wheel toe.

Front-wheel measurements are taken in reference to this axis.

Symmetrical axis 2

Centre line running through front and rear axles.

Fig. 15: Identifying Geometrical Driving Axis And Symmetrical Axis

Wheel misalignment

Angle by which one front wheel is displaced more towards front or rear than the other front wheel. The wheel offset angle is positive when the right wheel is displaced towards the front and negative when it is displaced towards the rear.

Fig. 16: Identifying Wheel Misalignment

Kingpin offset/scrub radius

Is the distance from the center of the wheel contact face to the intersection point of the kingpin extension. The line through the center point of the spring strut support bearing and the control arm ball joint corresponds to the "kingpin".

The scrub radius is influenced by camber, kingpin angle and wheel offset of the wheel rim.

Fig. 17: Identifying Positive And Negative Kingpin Offset

IDENTIFICATION OF SUSPENSION WITHOUT LABEL

NOTE: If the front spring strut does not have a label for suspension identification, the type of suspension can be identified from the part number in the Electronic Parts Catalogue.

INFORMATION ON REPLACING STEERING BOX AFTER ACCIDENT DAMAGE

Situation

In the event of accidents or driving conditions similar to accidents, shock-like loads can cause different types of damage to steering boxes. When a steering box is externally undamaged, it is sometimes only possible to identify damage with great difficulty and with great effort. However, damage of this nature poses an unacceptable risk to the vehicle because it can result in failure of the steering system.

Because of the disproportionate amount of effort involved, it is generally not sensible to check thoroughly all the individual components of the steering box and as an alternative it is necessary to take into account other components which can be checked more easily.

Procedure

The steering box must be replaced if one or more of the following points apply:

1. Visible or noticeable damage to the steering box
   • Version with electric steering box (EPS): Examine in particular the control unit with all plug connections for damage and hairline cracks.
2. Unacceptable torque increase and jamming when the steering box is turned from lock to lock (without hydraulic/electrical assistance)
3. Permissible tolerances exceeded during axle/wheel alignment (include alignment record with invoice/report if necessary)
4. Fire damage
5. Damage, permanent deformation or fractures to:
   • Wheel rims in the event of a negative result from the wheel/axle alignment check
   • Spring struts, steering stubs, wheel carriers
   • Wishbones
   • Leading or trailing links or anti-roll bars with this function
   • Body-side screwing/attachment points for wheel guide/control components
   • Front axle support
   • Pitman arms
   • Track rods
   • Steering gear fixtures
   • Steering Column

This guideline is binding for all accident repairs to BMW and MINI vehicles.

NOTE: If the steering box replacement work which is required for safety reasons is refused by the customer or an insurance company for cost reasons, a memorandum to that effect must be drawn up and countersigned by the party bearing the costs of the accident repair.

IMPORTANT: The vehicle's operating licence will be invalidated whenever the function of any of its safety components is compromised!

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