Originally Posted by enigma
Yes, active roll stabilization. The way BMW implemented it is not by varying the rate of the sway bars. Thats actually constant. What they do is apply a variable pre-load to counteract the tendancy of the car to roll when turning. Its basically a small motor that twists the bar in the center. It can also effectivly disconnect the bars if the motor is allowed to move freely.
Variable pre-load effectively accomplishes a variable rate. Sure the combined roll bar, end to end never has a higher torsional stiffness. But with the neutral (no torque) angular position having an offset angle by the actuator what was once no net twist on the sway at no torque becomes no net twist with a definite torque. So by varying this angular offset you do end up with an effective variable rate sway bar.
I'd think I'd still like to have EDC more than ARS. I am pretty happy with the very flat cornering provided by a good aftermarket sway bar (stock is never stiff enough with BMW for my liking). However, when going straight, over speed bumps or smaller high speed bumps in the road (under totally neutral sway bar action) decent track shocks are usually way to harsh. EDC offers a lot to improve this particular situation.
Both together is all the better.