This
system allows you to electronically adjust pre-load at the rear shock for
one-up, two-up or two-up with luggage and then separately adjust the rebound
damping between three levels: sport, normal, comfort.
Ploss
(BMW's head of chassis development) ,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.”
A
further description by BMW
The
second generation "Electronic Suspension Adjustment", or ESA II, allows the
suspension to be adjusted very comfortably and adapted to the riding mode and
load.
The selectable characteristic curves for suspension and damping enable a
previously unknown degree of adjustment of the chassis to road conditions and
load with the greatest possible operating comfort.
This system, which is unique within the motorcycle market, allows the driver to
adjust both the rebound-stage damping of the front and rear spring struts and
the spring mount ("spring preload") of the rear spring strut, but also its
spring rates and therefore the hardness of the spring by electronic means. This
is achieved in a convenient way by means of the multi-controller in conjunction
with the menu guidance on the TFT colour display.
To keep operations as simple as possible and to prevent mistakes when setting
the suspension, to begin with the rider only enters the loading status ("solo",
"solo with luggage" or "with passenger and luggage"). The adjustment of the
relevant spring mount or spring rate is then automatic, with the system
coordinating both of these values.
In addition, the rider selects the "Comfort", "Normal" or "Sport" damper setting
and therefore the required suspension character of the machine. Working with
these specification, the electronic controller uses the optimum parameters to
calculate the appropriate damping rates and uses an electric motor to set these
on the spring mount. In total, there are nine different variants available. The
damping rate is changed by means of small stepper motors on the dampers.
The additional adjustment of the spring rate allows the level of the motorcycle
to be perfectly adjusted to different loading states and thus ensures an even
higher degree of stability, maneuverability and comfort. Even under maximum
loading conditions, with passenger and luggage, full cornering clearance is
maintained, enabling a sporty riding mode. In addition, the adjustment of the
spring rate significantly reduces the danger of drifting under extreme loads.
It is possible to change the damper setting ("Comfort", "Normal" or "Sport" ) at
the press of a button, even while moving. For functional and safety reasons, the
spring mount can only be changed when stationary. An electric motor with
transmission is used to vary the spring rate.
The change in spring rate is facilitated by two springs switches in series. An
elastomer element (Cellasto) in combination with a conventional helical spring
below absorbs the forces during compression. The radial outward expansion of the
Cellasto element is permanently limited by a steel sleeve. On the inside, an
electro-hydraulic mechanism is used to move an aluminium sleeve. The position of
the inner sleeve influences the inward expansion of the Cellasto element and
therefore its spring rate. This has the same effect as the use of two springs of
different strength. If the inner sleeve sits on the steel spring, the Cellasto
element will not function and only the steel spring will work. If the internal
sleeve is then moved, it is also possible to vary the spring mount of the steel
spring, in other words the "spring preload".
The enables the static normal position and the rising geometry to be maintained
to optimum effect in all loading states. The additional adjustment of the spring
rate over the broad range from 110 to 160 N/mm made it possible to spread the
"Comfort", "Normal" and "Sport" settings broadly for ESA II, thereby clearly
influencing the riding mode.
The advantage of electronic suspension setting with ESA over a conventional
mechanical setting is the fact that all suspension components are immediately
coordinated, so that "normal users" can avoid errors. This will enable riders to
avoid the need for awkward and time-consuming manipulation of tools, instead of
which they can make the adjustment conveniently within seconds at the press of a
button. This makes it possible to adjust the suspension even at short notice,
for example when spontaneously carrying a passenger or when the characteristics
of the terrain suddenly change.
Review
These
past couple of weeks, four thousand miles of Blue Ridge Mountain and Cherohala
Skyway twisties, fire road riding in the Smoky Mountains, and open interstate
runs have given plenty of opportunity to confirm that this ESA system is a true
rider’s asset. No longer do you have mess around with suspension adjustment
tools or even twisting the preload dial on a rear shock, because it’s all there
in a single button:
Comfort, Normal, and Sport settings allow you to change rebound damping on the
front suspension, and rebound and compression damping in the rear while you’re
riding. Best Example of Use: Riding highways on a cool morning, the “Comfort”
mode was perfect. But a few hours later, 90+ Fahrenheit temperatures must have
thinned out the shock’s oil, and the bike was bouncing and “wallowing out” too
much. Just hitting the ESA button a couple of times to select “Normal” mode
fixed this instantly. Later on we were in some twisties, and the bike was
rocking back and forth a bit coming in and out of corners. A couple of clicks of
that ESA button to “Sport” steadied the bike and made it carve through each turn
with absolute precision. So cool!
Shock preload adjustments (that have to be adjusted while the bike isn’t moving)
offer up multiple combinations for a single rider, rider with luggage, riding
2-up, and the 2 firmest settings meant to handle extreme compression needs in
tough terrain. This basically compensates for extra weight or stiffening needs
by applying pressure to a piece of elastomer within the shock assembly. Best
Example of Use: As with many motorcycles, BMW figured the “typical rider" to be
about 175 lbs., and the R1200GS’s suspension was set up accordingly. If you
weigh more than this or are routinely changing your luggage and passenger
situation, just hit the ESA button and adjust accordingly. You’ll see the ride
height of the bike change while it’s parked and making it’s adjustments, as your
bike can move upward significantly during adjustment.
It won’t take long to memorize exactly which damping and preload combinations
work best for the ride you’re heading out on. Best part is, even if you got it
wrong or the road conditions change, most of what you’ll need to change is your
damping, which can be done while you’re riding.
Don’t overlook the safety factor here, either. The more accurately your
suspension is tuned for each riding situation, the more contact your tires will
have with the terrain below. Be it under braking or through turns, every little
bit of grip you maintain just might make the difference in a sudden reaction
need some day.
Comfort, enjoyment, safety, and agility are all factors in our riding success.
Next time you get the chance to upgrade to a system like BMW’s ESA, don’t pass
up the opportunity.