STUTTGART - Unconventional design is getting the blame for the apparent instability of the A-class during dramatic lane-change maneuvers.
At 3575mm long, 1941mm wide and 1601mm high, the Mercedes-Benz A-class forgoes traditional two-box small-car design for a radical one-box appearance.
By building a higher car to gain precious interior space, the car's critical center of gravity is raised. The center of gravity is 55mm higher than on the C-class, for example.
The result is a build up of inertia and increased body roll during hard cornering due to the greater proportion of the weight concentrated above the car's waistline.
Daimler-Benz attempted to counter this effect in the design by using a revolutionary platform structure that places the heavy engine and driveline as low as possible underneath a flat floor structure.
The design lowers the center of gravity and is supposed to be safer in a collision. The engine gets driven downward, below the occupants, instead of being pushed into the cabin.
The A-class has a relatively wide track for a car of such small dimensions (1500mm front, 1440mm rear), and a relatively long wheelbase (2423mm).
Daimler-Benz officials are silent about details relating to the A-class' polar movement properties, the crucial measurement which greatly effects handling.
Along with its high-roof design, another factor being singled out for the A-class' instability is its relatively stiff trailing-arm rear suspension.
The suspension saves space, but it permits little change in camber when subjected to strong lateral forces, with less predictability and faster breakaway at the outer limits of tire adhesion than other double-wishbone or multi-link suspensions.
Fitting the A-class with the Bosch electronic stability program may be expensive in the short term, but it is almost certain to solve the problem.
Using a series of yaw sensors to detect traction loss, it automatically applies braking pressure to whichever wheel requires it.
This immediately restores tire contact.
At the same time, an electronic throttle mechanism momentarily reduces torque loadings to the driving wheels in front, providing added stability.