<P> Another early semi-automatic transmission was the Sinclair S.S.S. (synchro - self - shifting) Powerflow gearbox. which was applied to Huwood - Hudswell diesel mines locomotives . It was also applied to some road vehicles . </P> <P> Modern "Semi-automatic transmissions" usually have a fully automatic mode, where the driver does not need to change gears at all, operating in the same manner as a conventional type of automatic transmission by allowing the transmission's computer to automatically change gear if, for example, the driver were redlining the engine . The semi-automatic transmission can be engaged in manual mode wherein one can up - shift or down - shift using the console - mounted shifter selecter or the paddle shifters just behind the steering wheel, without the need of a clutch pedal . The ability to shift gears manually, often via paddle shifters, can also be found on certain automatic transmissions (manumatics such as Tiptronic) and continuous variable transmissions (CVTs) (such as Lineartronic). </P> <P> Despite superficial similarity to other automated transmissions, semi-automatic transmissions differ significantly in internal operation and driver's "feel" from manumatics and CVTs . A manumatic, like a standard automatic transmission, uses a torque converter instead of clutch to manage the link between the transmission and the engine, while a CVT uses a belt instead of a fixed number of gears . A semi-automatic transmission offers a more direct connection between the engine and wheels than a manumatic and this responsiveness is preferred in high performance driving applications, while a manumatic is better for street use because its fluid coupling makes it easier for the transmission to consistently perform smooth shifts, and CVTs are generally found in gasoline - electric hybrid engine applications . </P> <P> Typically semi-automatic transmissions are more expensive than manumatics and CVTs, for instance BMW's 7 - speed Double Clutch Transmission is a CAD 3900 upgrade from the standard 6 - speed manual, while the 6 - speed Steptronic Automatic was only a CAD 1600 option in 2007 . In a given market, very few models have two choices of automated transmissions; for instance the BMW 545i (E60) and BMW 645Ci / 650i (E63 / 64) (standard 6 - speed manual) had as an option a 6 - speed automatic "Steptronic" transmission or a 7 - speed Getrag SMG III single - clutch semi-automatic transmission until after the 2008 model year, when the SMG III was dropped . Many sport luxury manufacturers such as BMW offer the manumatic transmissions for their mainstream lineup (such as the BMW 328i and BMW 535i) and the semi-automatic gearbox for their high - performance models (the BMW M3 and BMW M5). </P>

What is difference between automatic and semi automatic cars
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