semi-auto means its auto but instead of just P, N, D, R you get
one more section for +/- (or in some instances 1,2,3,4,5) which
means you can select the gear you want. (cos D will select and
change gears for you)
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STEPTRONIC is bmw's version of a semi-auto transmission
[FROM BMW]Steptronic converts a BMW automatic transmission into a
manual gearbox whenever required. In the BMW 7 Series, the
Steptronic keys are located on the steering wheel. In other models,
drivers use the selector lever, moving it from position D
(automatic mode) to sports program S.
To choose gears individually according to your personal
requirements, just tap the selector lever briefly backward into
position S in order to shift up, and forward in order to shift
down. This function allows you to shift gears actively without
having to operate the clutch.
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TIPTRONIC is porsche's version of a semi-auto transmission
[FROM PORSCHE.COM] This versatile system combines automatic
transmission with the option of manual gearshifts.
For manual control, simply slot the gear selector into the manual
gate and use the gearshift controls on the steering wheel. Press up
to change up, and down to change down. Gearshifts are performed in
around 0.2 seconds with virtually no interruption in drive. The
action is comparable with that of a manual gearbox.
Switch to automatic, and you can still change gear by hand using
the rocker controls on the steering wheel. This race-derived
function is particularly useful when performing an overtaking
manoeuvre. If there is no manual input for a period of eight
seconds, the system will revert to automatic mode. The drive
position and gear selection are displayed at all times on a
dedicated cockpit display.
In automatic mode, Tiptronic S can choose from a range of shift
points for every gear. The standard gearshift pattern, designed for
maximum fuel economy, can be steplessly varied up to a dedicated
Sport configuration for optimum high-performance driving. Each
gearshift point is automatically selected based on current driving
style and road conditions. Within a short space of time, youll
develop a feel for the system and begin to influence gearshifts
using the throttle alone. The benefits of Tiptronic S are
particularly apparent when exploring the cars performance. Even in
automatic, the rapid gearshift action enables exceptional agility
from the car.
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SMG (Sequential Manual Gearbox) is bmw's hmm. i'll lift copy and
paste from bmw.com:
BMW's Sequential Manual Gearbox is based on the conventional manual
gearshift. It possesses one particular innovation however: not only
is there a regular gearstick, but two switches or paddles on the
steering wheel enable drivers to change gears, up and down, without
even so much as taking their hands from the wheel.
The gear change process is sequential - none are skipped over - and
not by simply selecting one particular gear as is the case with
conventional systems. Precision hydraulics ensure that gear changes
are completed in less than 150 milliseconds; the driver does not
need to use the clutch or ease off the accelerator.
Three programs are available: normal, manual, sporting manual (for
faster gear changes) and the cruise mode (automatic gear changes
without manual input). The Sequential Manual Gearbox eliminates
inaccurate gear changing and the accompanying irritation of
grinding gear cogs.
