Design Layout: Notes

Index	Explanation
1	Spring strut
2	Transverse control arm, top
3	Swivel bearing
4	Wheel bearing
5	Stabilizer link
6	Transverse control arm, bottom
7	Stabilizer bar
8	Tension strut with hydraulic mount
9	Front suspension subframe

The introduction of a second control arm level for wheel control, which is arranged above the wheel, results in additional degrees of freedom for the kinematics of the front axle as well as for the suspension/damping compared to other designs such as a spring strut front axle.

Components with special materials:

• The forged aluminum swivel bearing (3) with the 3rd generation wheel bearing (4).

• The transverse control arm at the top (2) is made from forged aluminum and the cylindrical joint pin is clamped in the swivel bearing (3).
• Tension strut with hydraulic mount (8) and lower transverse control arm (6) are forged aluminum components while the lower control arm bears the spring strut (1) by means of a forged steel mount.
• The new front axle subframe (9) is a welded aluminum structure which, as the standard axle, does not require the familiar aluminum thrust panel with service openings for increasing stiffness. This is made possible by the solid transverse section in the front axle subframe.

Kingpin offset at hub 

Index	Explanation
1	Steering pivot axis
2	Wheel center plane
3	Kingpin offset at hub

The steering pivot axis of the wheel suspension is now formed by a joint at the top A-arm and the virtual pivot point of the lower arm level as known from the spring strut or McPherson front axle.

The steering pivot axis is therefore freely selectable and can be positioned such as to produce a small kingpin offset at hub with sufficient weight recoil.

This kingpin offset at hub is decisive for transmitting the irregularities on the road surface to the steering wheel. The lower and upper arm levels now move simultaneously in response to wheel deflection. As a result, as the spring compresses, the wheel pivots in such a way that the negative camber to the road does not decrease as much as is the case with a spring strut front axle.

Since the two control arm levels undertake the wheel control, the damper is virtually no longer subjected to transverse forces and rotational motion.

This makes it possible to do without a roller bearing assembly (conventional strut mount) on the spring strut support. Instead of this conventional roller bearing a damping and support unit is installed that takes up all three load paths. The load paths are the damper piston rod, the inner auxiliary spring and the bearing spring. This damping and support unit is still referred to as the "strut mount".

Due to the lack of transverse forces, the piston rod can be made thinner, resulting in a similar displacement volume in the push and pull direction of the damper. This serves to improve the design layout of the damper and is the prerequisite for the innovative damper control system - vertical dynamics control (VDC).

Due to the substantially lower friction at the circumference of the piston rod, the damper can respond more sensitively.

By connecting the stabilizer bar via the stabilizer link to the spring strut, the torsion in response to body roll motion is equivalent to the total wheel lift from the inside to the outside of the curve (in other suspension setups, the stabilizer bars are connected to a transverse control arm and therefore achieve only a fraction of the torsion angle). Despite being highly effective, this high degree of torsion allows for the stabilizer bar to be made relatively thin which has a favorable effect on driving comfort and dynamics as well as saving weight.

Comparison of front axle technical data 

Description (Front axle data)	E65/E66	F01/F02
Kingpin offset at hub (mm)	88.1	56.3
Track width (mm)	1578	1611
Camber	-0° 20' ±20'	-0° 12' ±15'
Camber difference	0° ±30'	0° ±30'
Total toe-in	10' ±8'	16' ± 6'
Turning circle (m  /ft)	11.92  /39.10	12.15  /39.86
Kingpin offset (mm)	0	0.5
Toe angle difference (toe out on turns)	1° 27' ±30'	12° 20'
Caster angle	7° 27' ± 30'	7° 0'