Car manufacturers select different transmissions based on the type of vehicle and the experience they want to deliver to drivers.
That’s why almost all supercars or sports cars have dual clutch transmissions as it provides driver engagement and better performance from its fast shifts.
In contrast, luxury or more mainstream cars prioritize comfort and smoothness over performance. For these vehicles, the conventional automatic transmission, also known as a torque converter, is often the first choice. These transmissions are smoother and offer fluid acceleration and seamless gear shifts. In modern iterations, even these automatics have become highly responsive, offering quick enough shifts for most cars.
On the lower end of the market, in economy or entry-level cars, manual transmissions and CVTs are common choices due to their lower cost. These transmissions are simple, inexpensive to produce, and offer good fuel efficiency for daily city commuting. However, the dual-clutch transmission has also found its way into these more affordable, compact cars, which at first glance may seem counterintuitive. After all, DCTs are known to be more complex and costly to manufacture than their manual or CVT counterparts.
The big question, then, is why DCTs are used in such different applications-from track-focused performance cars to compact economy city cars. While dual-clutches shine in high-speed, performance driving, they are often criticized for being jerky at low speeds, especially in stop-and-go city traffic. In fact, almost every other transmission type is more suited for slow-speed driving because of the inherent difficulty DCTs face in smoothly engaging and disengaging their two clutches at lower speeds.
DCTs are quite complex, have two separate clutches-one for odd gears and one for even gears-basically two manual transmissions put together, it may seem simple but making everything work seamlessly and with fast shifts is quite complicated. It is also less reliable and more expensive to fix than normal automatics, not that manufacturers care about this, but I thought it would be nice to mention. But it does offer better fuel economy as the shifts happen almost instantly resulting in minimal power loss. Also the mechanical connection between the engine and the transmission is more direct, leading to higher efficiency.
Torque converters on the other hand use a simpler fluid coupling mechanism to transfer power from the engine to the wheels. While still sophisticated, the torque converter's design is simpler to manufacture compared to a dual-clutch system. And it's produced in much greater quantities than dual clutches which reduces costs even further. But it’s less efficient when compared to the dual clutch as it shifts slower which results in wasted energy during gear changes. They also have hydraulic components that create resistance and reduce overall mechanical efficiency compared to a DCT.
There was a time when everyone thought that DCTs were the future, as it seemed like the perfect solution for combining the best of both worlds: the manual driving experience and the convenience of an automatic, but as years go by, this idea is being faded slowly.
Modern torque converters have become much faster, with improvements in shift speed that rival those of dual-clutch transmissions. While DCTs still have the edge in terms of ultimate shift speed and engagement, the differences are becoming less noticeable, especially in real-world driving conditions. When you combine the smoother operation of a torque converter with its ability to handle high torque loads and lower manufacturing costs, it becomes clear why automakers like BMW are making the switch.
But surprisingly, when everyone thought BMW was done with DCTS, they reintroduced the dual-clutch transmission (DCT) last year, this time not in its high-performance models but in its front-wheel-drive cars. Models like the latest 1 Series, X1, and X2 are all now equipped with DCTs. What's more interesting is that while these more mainstream cars are getting DCTs, the track-focused M4 CSL-which you would expect to have a DCT-features a torque converter automatic instead. So, what's the logic behind these decisions?
The reintroduction of DCTs in front-wheel-drive models like the 1 Series, X1, and X2, however, isn't about performance-it’s about packaging. These compact Front-wheel-drive cars have more limited space for components like transmissions. The DCT is typically more compact than a traditional torque converter automatic because it doesn’t require the bulky torque converter unit, which is necessary for automatics with planetary gear sets and complex hydraulic systems. DCTs, on the other hand, use a pair of clutches (one for odd gears and one for even gears), which are often housed in a relatively small casing.