Differences between automatic and semi-automatic gearboxes

We explain the differences in how a semi-automatic gearbox functions compared to ones running fully automatically.

Conventional cars nowadays will come with either a manual or automatic gearbox but there is a variation of the latter known as the semi-automatic gearbox.

Finding a car which has a gearbox that only works in a semi-automatic manner is very rare nowadays, thanks to the rise of dual-clutch systems. But many of the new cars on the market nowadays which offer a dual clutch/automatic gearbox can be operated by the driver in a semi-automatic fashion if they choose.

Semi-automatic gear changes explained

A gearbox that works semi-automatically (also known as automated manual) requires the driver to make gear changes themselves, like with a manual gearbox. The key difference is that while a manual ‘box requires the use of a clutch pedal, a semi-automatic removes this part from the driver’s reach and completes its function electronically.

Since electronic equipment takes care of the clutch, the gearbox can time its gear changes to the torque of the engine and make each gear change fast, precise and smooth.

However, some gearboxes that change gears electronically can struggle completing this function as quickly and as smoothly as drivers would want when the car makes a sudden change of speed following, say, heavy braking. Because of this, a semi-automatic function can prove more appealing to drivers.

With no clutch pedal or large gearstick necessary, someone who drives a car semi-automatically will use either a small gear lever with simple up or downshift changes or use paddles mounted on the outside edges of the steering wheel. A gearbox that can be used semi-automatically and includes these paddles is known to some by the informal term ‘flappy-paddle gearbox’.

While there is less effort and engagement involved than with a manual gearbox, driving a car semi-automatically still gives the driver the pleasure of pushing the car through the gear ratios using a gear-selecting-lever.

Popular examples of gearboxes in current new cars which offer automatic and semi-automatic functionality include the Volkswagen Group’s DSG, Ford PowerShift and BMW DCT.

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