DYNAMIC ESA A look inside BMW’s semi-active suspension
For a bit of insight into how Dynamic Electronic Suspension Adjustment works, I sat down with BMW’s head of chassis development, Jörg Ploss. I told him how much we enjoyed the pushbutton ESA II on theK1600GTL long-term bike we’d had and his comment was, “Yes, but this is old!”
According to Ploss, 90 percent of BMW’s motorcycle buyers opt for ESA, whereas only 25 percent of BMW car buyers select electronically adjustable suspension from the options sheet. Just shows how much more dedicated we two-wheelers are to seeking maximum performance.
Ploss explained that a separate ECU is dedicated to Dynamic ESA, and it is fed information from various systems and sensors on the bike.
The key sensors are potentiometers that measure position of the suspension front and rear, as well as the velocity at which the units are compressing or extending. While the HP4 sportbike’s semi-active system uses a potentiometer only at the rear, use of two potentiometers on the all-terrain GS gives the system better information about the attitude of the bike. Information from the ABS and a lean-angle detector are also used to influence the damping-control valves contained in the heart of the front and rear shocks.
The system will, for example, tighten rebound on the front shock on corner exits to help control chassis pitch and also increase overall damping when braking hard. Damping also gets more taut as lean angle increases.
The valves, buried in the hearts of the shocks, were first used on the previous-generation 7 series sedan. In fact, they’re still in use in the M3 and M5 cars.
Operation is by a solenoid that pulls the control valve against spring pressure. If there is no electric signal, maximum damping control is at play. Applying current moves the control valve progressively to reduce damping.
The system reacts almost instantly, whether you clamp hard on the brakes, hit deep lean or select Soft, Normal or Hard ESA settings using the left-handlebar switch. The change from Hard to Soft settings is quite noticeable, but you are unlikely to detect the operation of the system overall, except in perhaps how well-controlled and planted the chassis feels in all riding conditions.
Dynamic ESA retains the rider-selected electronic control of spring preload, as on previous systems. It is not truly “dynamic.”
I asked Ploss about the possibility of dynamically adjustable ride height that might lower the bike during braking to reduce the chance of stoppies, or the ability to change chassis attitude for corners and allow quicker turn-in. And what about increased ride height in off-road conditions? “There must be some things left for us to develop,” he said with a smile.