BMW K 1300 GT User Manual

Page 23

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BMW

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Information

10/2008

Page 23

(with short leverage to the wheel/road contact point), forces and momenta are
fed into the frame in a smooth process, again reducing any loads acting on
the frame structure.

The front-wheel suspension combines supreme stiffness with minimum
weight, since the design and confi guration of the wheel carrier may be freely
chosen also in its contours due to the cast structure and may therefore be
adapted precisely to the force curves. Appropriate wall thickness determined
spec fi cally according to local load conditions reduces the weight of the frame
without forfeiting any strength or stiffness. And taking the main direction of
forces into account, the longitudinal arms are set up mainly to absorb forces in
their longitudinal direction, that is inbound and rebound forces, a structure
which again makes them particularly stiff.

The lower longitudinal arm previously made of forged steel is replaced by
a light-alloy forging on the K 1300 S. Through its light but nevertheless
extremely stiff confi guration, this new arm guarantees an even more sensible
and transparent response, at the same time reducing unsprung masses
by approximately 1 kg. Hence, the overall structure weighs a mere
12.7 kg/28.0 lb, as opposed to 13.7 kg or 30.2 lb on the K 1200 S.

The geometry of the spring strut pivot point follows a slight progression,
with 115 mm or 4.52" of spring travel (60 mm/2.36" inbound, 55 mm/2.16"
rebound). At 32

o

right and left, steering lock complies with the usual standard

in this class.

A new feature is the upper fork bridge on the new K 1300 S which, through its
open design, helps to save weight and gives even greater emphasis to the
sporting and dynamic character of BMW’s new high-performance machine.

Through its kinematic behaviour, the Duolever also serves to set off brake
dive, which remains virtually unchanged throughout the motorcycle’s
complete range of spring travel. Longitudinal forces acting on the front wheel
when applying the brakes cause hardly any inbound spring action, only the
dynamic distribution of wheel loads leading to a certain dive effect giving
the rider through the telescopic fork the usual feedback on how hard he is
applying the brakes. Hence, the Duolever combines the feedback from
the front wheel so important to the sports rider with the comfort and safety
benefi ts of an anti-dive set-up.

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