M3 chassis: the best of 3 Series and BMW M engineering:

In developing the M3, BMW M engineers set for themselves the target of making the great-handling 3 Series even more capable. Here's what they did:

Front suspension. While retaining the basic concept of both E36 and E46 3 Series, BMW M stayed close to the E36 M3 in terms of the system's kinematics (its arrangement and movements of components as the suspension works over bumps and in curves). At the same time, the new M3 system takes advantage of E46 developments, including the wider front track and aluminum lower arms. Specifically:

o At 59.4 in., the M3's front track is 1.5 in. greater than that of the 330Ci models.
o As on the 3 Series, weight-saving, strong forged-aluminum lower arms are employed. But these arms are unique to the M3.

To form an ultra-rigid basis for the suspension system, the BMW M engineers created a new thrust plate to handle the immense lateral thrust generated by the M3's tires in cornering. It is made of aluminum 3 mm thick, and attaches in the area between the left and right lower suspension arms. The thrust plate even incorporates an NACA air intake that takes in air to cool the transmission.

The bearings, bushings and cushions on which the suspension arms pivot are also specific to the M3. In contrast to the arc-shaped lower arms of current 3 Series models, the M3's unique lower arms have a "bat wing" shape that achieves even greater strength. As on the regular models, they are made of forged aluminum to keep unsprung weight low and strength high.

Other M3-specific front-suspension components include:

o Unique steering knuckles
o Modified wheel bearings
o Separate top mountings for the springs and shock absorbers; on standard 3 Series models they mount together.
o Subframe - from 3 Series Convertible, even for the M3 Coupe
o Reinforcing braces to the strut towers, visible with the hood open.

Steering. Power assist is calibrated for extra-firm road feel, and steering return action is enhanced by the increased caster.

Rear suspension. The track is also increased here (by 1.6 in.), and both pairs of lateral links (lower and upper) have steel balljoints instead of rubber bushings at their outer ends. There are many other detail distinctions from the standard rear suspension as well.

For the larger, stronger M3 differential, M engineers developed an entirely new mounting system that uses one bushing at the front and two at the rear, just the opposite of the standard 3 Series setup. In BMW's usual "acoustically decoupled" mounting, the differential mounts through these bushings to a subframe, which then attaches to the main structure through four rubber mounts. This subframe is specific to the M3, having been developed to accommodate the larger differential assembly.

BMW M also added a V-brace to stiffen the subframe's attachment to the main structure. This is analogous to the thrust plate at the front, adding rigidity where the suspension joins the vehicle structure.

As the most prominent element of the multi-link rear suspension system, the massive Central Link is retained. The link pivots on a large rubber bushing at its forward end; this element is firmer in the M3 than in "regular" 3 Series models. The axle halfshafts are upsized for extra strength, and the wheel carriers are special to the M3 as well.

Springs and shock absorbers. The M3's coil springs have been carefully calibrated for an ideal blend of firmness and compliance. Its twin-tube gas-pressure shock absorbers - with hollow piston rods to minimize inertia and mass - are likewise perfectly calibrated for sports-car response. Anti-roll (stabilizer) bars - 26 mm front, 21.5 mm rear -are sized for ideally responsive, yet not nervous, handling. All this has been confirmed and re-confirmed on the BMW Proving Ground's handling course and at the famous N