Twin-clutch gearboxes: what's all the fuss

It's one of 21st century motoring's great win-wins. Or win-win-wins, even -- a technology that works to the benefit of greens, hoons and penny-pinchers alike. Twin-clutch sequential manual or semi-auto transmissions spread through the world in 2008 faster than rumours about Britney Spears's mental health. 

They work using various configurations but in simple terms can be categorized as using separate clutches for odd and even gear clusters. This allows them to pre-load the next gear ratio and its clutch in the gear sequence for up or downshifts, changing not just gears, but clutches simultaneously. 

Thus during acceleration, each outgoing gear gives its incoming successor maximum leg-up. No stopping for breath.

As usually happens with automotive advances, the Germans have been the early adopters. Volkswagen pioneered its market popularisation with its Borg Warner-sourced Direct Shift Gearbox (DSG). They did this by not reserving the DSG for upmarket R-Series models and Audis, but by taking it to mass market on most Passat, Golf and Jetta models, Skodas and Seats. A long way upmarket, its Bugatti Veyron uses a posher system from UK engineers Ricardo.

Others cottoned on fast. BMW added an extra clutch to make the most of the 2008 E90 M3's 309kW V8. Porsche replaced its old Tiptronic system with a twin-clutch unit called PDK (Porsche Doppelkupplung, if you must know). 

Nissan's revived GT-R "Godzilla" has it. Ford is rolling out its Getrag-sourced PowerShift unit through its Euro models and other brands like Mitsubishi have bought into the same action. 

Indeed, because it neatly bridges the gap between traditional manual and auto options, it's only a matter of time before someone serves it up to mainstream buyers as one-size-fits-all standard, no options. 

A PROPER CLUTCH WITHOUT A CLUTCH PEDALIf you think that extra clutch is all about boosting performance figures, you're half right. Because it's all about maximising the efficiency with which the transmission puts engine power to the road, it's as much about fuel economy as it is about performance. 

It starts with an idea that goes back a way -- the "clutchless manual". Formula One has been playing with it since the 1970s; it was mainstream fare there from the early 1990s. 

The idea is simple: replace human legs and arms with electronics and hydraulics to disengage the clutch, change cogs and reengage the clutch because they can do it much, much faster. That means they cut "torque interrupt" -- the power-down period during manual gearchanges that ruins the flow of torque from engine to road, making the car work harder than necessary to build and rebuild momentum.

Thanks largely to advances in onboard computing power, the latest sequential boxes can also work in full auto mode without the slippy characteristics that cruel the efficiency of conventional torque converter-driven "slush boxes".

All of which means they combine the best of auto and manual driving into a single gearbox that's as much fun on that twisting coast road as it is relaxing on the dull freeway home. 

TWO CLUTCHES BETTER THAN ONEAdding a second clutch takes this one step further. How? By having the second clutch ready to engage at the same time as the cog. This makes the process much faster. 

How much faster? If you're executing complete changes in less than a second with a clutch pedal, you're a good driver in a good car. The normal time quoted for a F1 car with an automated single clutch is 30 milliseconds. Volkswagen claims DSG can do it in as little as 8 milliseconds.

All of which eliminates the need for expertise in making the most of a manual transmission. Because it takes considerable skill to do that with a clutch pedal -- skill most of us don't have. We have neither the rev-matching acumen nor the physical dexterity to do this, nor the time or the inclination to learn. 

For those of us merely wanting to get from A to B, it's easier to live with torque-interrupt than it is to learn what it is and how to minimise it. At least until we start feeling the costs in energy, petrol and therefore money, not to mention environmental wellbeing. And probably even then...

With that extra clutch, we don't have to worry about that any more. It does all the thinking and rev-matching for us. 

So there's something in it for enthusiasts and A-to-B trundlers alike. 

It's a technology that helps even the stupidest and laziest among us squeeze every bit of efficiency out of the engine. Meaning it accelerates faster and uses fuel more efficiently, which helps maximise the energy we squeeze out of every fuel dollar.

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