· 61 ·
The 911 | Transmission
In comparison with a viscous
mult iplate clutch , where clutch
regulation is not init ia ted until
there is a difference in speed
betw een the front and rear axles,
the electronically controlled
mult iplate clutch responds much
more rapidly. Through conti nuous
monitoring of driving con ditions,
the electronics are able to
respond to a variety o f situations.
Sensors check, amo ng other
variables, the rotation speeds of
all four wheels, the longi tudinal
and lateral acceleration of the
vehic le , and the steering angle.
By evaluating the sensor dat a,
the system can quickly adjust
the distribution of drive force to
the front axle in order to ach ieve
optimal balance. If the rear
wheels threaten to spin under
acceleration, a greater p roportion
of drive force is sent forward
by a more powerful engagement
of the multiplate clutch. At the
sam e time, ASR prev ents the
rear wheel s from spinning. When
cornering, the front wheels only
ev er receive as much drive force
as is necessary to prevent lateral
instab ility. On uneven surfaces,
the rear differential fitted
as standard to all-wheel-drive
models, in c ombination with
ABD, also improves traction.
In this way, PTM, in conju nction
with Porsche Stab ility
Management (PSM), en sures
that the perfect distribution of
drive is achiev ed every time.
PTM really comes into its own
in we t condi tions or in ice and
snow. In these conditions, the
car’s acceleration capability
is simply breathtaking.
The result: a high level of safety
and outstand ing performance.
Put to use in the most
intelligent way.
Mechanically locking
rear differential.
A mechanically locking rear
differe ntial is standard in the
911 all-wheel-drive vari ants
a nd is available as an option
for all other 911 models in
conjunct ion with 19 -inch wheels.
It further enh ances tractio n at the
driven rear axle on uneven roads
and when accelerating out of
tight curves. This is accomplished
by the damping of l oad-change
reactions during fast cornering.
English 
