Electronic Suspension Adjustment second generation, or ESA II, is a technology offered in BMW’s bikes, where the rider can adjust the suspension settings at the touch of a button, according to load and preferred riding style. The system can electronically adjust the rebound damping on the front and rear struts, spring preload, and also the spring rate.
Here’s how the system works: The damping rate is modified at the dampers by means of small step motors, while the spring rate is changed with two springs connected in series. Here, the compression forces are absorbed by an elastomer element (Cellasto) combined with a conventional helical spring installed below. The outward radial expansion of the Cellasto element is permanently contained inside a steel sleeve. On the inside, an aluminium sleeve is moved electro-hydraulically. The position of this inner sleeve affects the inward expansion behaviour of the Cellasto element, and therefore its spring rate. This has the same effect as two springs with different tightness. When the inner sleeve comes up against the steel spring, the Cellasto element loses its function, and only the steel spring is acting. When the inner sleeve is then moved further, the spring preload can be varied.
This system helps the rider change suspension settings according to load and road conditions almost immediately, and helps maintaining a standard ground clearance at all times, eliminating the bottoming out effect. A total of nine combinations are possible with the system: three load settings, solo, solo with luggage and solo with pillion and luggage, combined with three damper settings, Comfort, Normal or Sport.