BMW's ESA II suspension -- available on the K1300S, K1300R and K1300GT -- is the first in the world to offer an adjustable spring rate. In addition to that spring rate -- the amount of force it takes to compress the spring or its "hardness" -- ESA II can alter preload and offers on-the-fly adjustment of the compression and rebound damping; basically, you can fully adjust your suspension at the touch of a button to a greater degree than ever thought possible. But how does it work?
On previous suspension units, adjusting the spring rate -- thus
providing equal handling no matter the weight carried by the motorcycle
-- was only possible by stripping down a shock and replacing
its spring for one of a different weight. BMW gets around this by
adding a polyurethane bushing to the top of the spring, meaning
suspension movement basically passes through two springs; the actual
spring and the bushing. By altering the rate at which that polyurethane
compresses, BMW is able to alter the effective overall spring rate.
Of course, it's not that simple. In order to precisely control the rate
at which the special polyurethane material -- called 'Elastogran' --
compresses and expands, BMW contains it within a sleeve located around
the shock's damper unit. An inner collar slides up and down in the
space the Elastogran expands into under compression, reducing that space
to make the force required to compress it greater or increasing the
space to make the required force less. That collar is actuated by ESA
II's computer and moves through three positions based on settings
chosen by the rider.
Those three settings are: "Solo," "Solo with Luggage" and "With
Passenger and Luggage." All three are represented by symbols in the
instrument panel rather than awkward phrases and are only adjustable
while the machine is stationary. These settings also control the amount
of preload, or the amount of force required to initiate spring
compression, which effectively alters the ride height.
In addition to those three, there's also settings for "Normal,"
"Sports" and "Comfort" modes, which alter the rebound and compression
damping rates. BMW claims that ESA II offers a greater degree of
adjustability to damping settings than its previous system.
The latter set of three settings is adjustable on the move and also
affects the spring rate, which will be automatically adjusted to suit
the chosen performance parameters.
The degree to which the shocks are adjustable varies front to rear
(remember that the K-Series range uses Paralever front suspension), it
appears that the front spring rate is adjustable only while stationary.