Sunday, 17 February 2013


The suspension of a car is what holds the wheels to the chassis, and is critical to good handling.

The front features an M Double Wishbone suspension.

"Double-Wishbone" means that that there are two main supports for the wheel, each of which looks like a wishbone. In the illustration above these as (2) and (5). There is also a "trailing link" (8) for additional support. The car is steered by means of the track rod (7) hooked up to the steering box (11).

In the F10, but all components are M-specific. There is also a 2.45 cm anti-roll bar (10) and a stiffening plate (12). The axle is attached in a more rigid fashion to the chassis than is usual, promoting increased torsional stiffness for better handling. It is made mostly from Aluminium to save weight.

The double wishbone in the F10 is an improvement over the McPherson strut system in most other cars, and also the E60 5-Series. With the MacPherson strut, the springs and dampers hold the weight of the car. With the double wishbone, they do not, and the springs and dampers are therefore more able to do their jobs. The MacPherson strut cannot allow vertical movement of the wheel without changing geometry relative to the road surface. The double wishbone is inherently superior in this regard. The MacPherson strut also transmits road noise and vibrations to a greater extent than does the double wishbone. Finally, the double wishbone allows for more freedom in the setting of camber and roll centre  thus allowing the engineers to provide a better setup for handling purposes. The double wishbone tends to be more expensive and complex than the MacPherson strut, and it also can handle a heavier car.

The rear axle is also mainly made of Aluminium and is as follows.

It is an M Integral IV multi-link suspension with a 2.15 cm roll-bar (2), stiffening plate (1), and is directly attached (without rubber bushings) to the chassis for increased stiffness. Attaching the axle to the chassis without rubber bushings is uncommon in street cars, but standard for race cars. It is possible in the M5 because the base F10 starts with a very stiff chassis to being with.

This suspension incorporates “elastokinematics” that allow each wheel to move and flex individually without loads and forces through the subframe to the opposing wheel. It has been in use since the E39 5-Series, and the one in the F10 M5 was taken virtually unchanged from the E60 M5.

The standard F10 has moved on to the Integral Link V, as it supports rear wheel steering that assists in parking and in stability control. The M5 eschewed rear wheel steering as being not worth the weight.

As with any suspension, there are springs and shock absorbers at all four wheels. The springs allow the wheels to bounce up and back down when hitting bumps, the shocks prevent them from continuing to bounce.

The shocks in the F10 M5 are under electronic control, and can be stiffened or loosened very quickly in response to changing situations in order to optimize both comfort and handling.

The system is called M VDM (for M-Specific Vertical Dynamics Management). The shock absorbers were developed with ZF Sachs and adapted to the M5. This is the VDC II (Vertical Dynamics Control System II) system that uses independent extension (A) and compression (B) adjustment via two sets of valves and works on the frequency at which the body of the car is oscillating to damp it.

The M VDM control unit gets signals from ride height sensors. The Electronics Damper Control (EDC) works with infinitely variable valves in the dampers. The hydraulic oil flow is regulated by the electromagnetic control valves. Control variables such as the ride height, front wheel speeds, steering angle, body movements and damper piston speed are used. Vertical acceleration between the suspension and body is monitored by the ride height sensors of the headlights. There is one ride height sensor installed at the front left and one at the rear left. They are hard wired to the Integrated Chassis Management control unit which sends these signals over FlexRay to the M VDM control unit.

The fundamental control principle is known as the “Skyhook system”, because the primary objective is to hold the vehicle stationary in a vertical direction. An overall analysis is performed of the ride height data, z-axis acceleration rates, and steering inputs (e.g. transition from straight-ahead travel to cornering). If M VDC detects a rapid increase in the steering angle, the controller infers that the vehicle is entering a bend and can preventively adjust the dampers on the outside of the bend to a harder setting in advance. Moreover, VDC is able to detect the braking operations by the driver based on the brake pressure information supplied by DSC. A high brake pressure normally results in pitching of the vehicle body; VDC counteracts that effect by setting the front dampers to higher damping forces. This also results in an improvement in the front/rear brake force distribution, which in turn reduces the braking distance.

The driver can set the system to Comfort, Sport, and Sport+ for increasing levels of stiffness.

This set by means of the shock absorber symbol near the gear shift lever (third from the top on the left).

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