While it is true that most performance-oriented motorcycles traditionally feature manual transmissions, there has been a recent trend of introducing big bikes with automatic transmissions. These automatic transmission-equipped motorcycles provide riders with the convenience of effortless shifting and a more relaxed riding experience. This shift towards automatic transmissions in larger motorcycles offers a wider range of options for riders who prefer the convenience and ease of use provided by automatic shifting.
Indeed, when it comes to specific motorcycle categories, different transmission types are commonly used. Maxi-scooters typically utilize continuously variable transmissions (CVT), which offer smooth and efficient power delivery suited for urban commuting. On the other hand, adventure bikes and cruisers often feature dual-clutch transmissions (DCT), providing the convenience of automatic shifting while still maintaining a level of control and performance. Each of these transmission types has its own set of advantages and disadvantages, and they operate in distinct ways to cater to the specific needs and preferences of riders in their respective motorcycle categories.
Continuously Variable Transmission (CVT)
In a CVT scooter transmission, there are two primary components: a pair of variable-diameter pulleys and a flexible belt. Each pulley consists of two halves, and their diameters can vary. One pulley is connected to the engine's output shaft, while the other is connected to the scooter's driven wheel. The belt loops around both pulleys, forming a continuous loop. Unlike traditional transmissions with a fixed number of gears, a CVT offers an infinite number of gear ratios within a specific range, providing seamless acceleration and optimal performance.
As the engine revs increase, the pulleys adjust their diameters by moving the halves closer together or farther apart. When the engine's output shaft rotates at a higher speed, the pulleys adjust to a smaller diameter, causing the belt to ride higher on the pulleys' sides. This reduces the effective gear ratio and increases the scooter's speed. Conversely, when the engine's speed decreases, the pulleys expand in diameter, causing the belt to ride lower on the pulleys' sides. This increases the gear ratio and provides better torque for acceleration.
What are the pros and cons of a CVT?
The Continuously Variable Transmission (CVT) offers several advantages. It is considered one of the best transmissions for optimizing efficiency due to its ability to vary the gear ratio seamlessly. The CVT provides a linear power band, allowing the engine to maintain its peak torque and power rev range for longer periods. Additionally, the technology behind CVTs has been refined over the years, resulting in their general reliability and dependability.
While the Continuously Variable Transmission (CVT) has its advantages, it also comes with a few drawbacks. One of the criticisms is its perceived boring and lackluster character, as it may not provide the same engaging driving experience as traditional transmissions. Another concern is the driveline loss that occurs due to the slippage in the CVT system, which can affect overall efficiency. Moreover, CVTs are not well-suited for high-power output engines, as they typically reach their maximum potential at around 50 horsepower, making them more commonly used in scooters rather than performance-focused two-wheelers.
Dual-Clutch Transmission (DCT)
A Dual Clutch Transmission (DCT) is a type of transmission used in motorcycles that combines the benefits of both manual and automatic transmissions. It utilizes two separate clutches—one for even-numbered gears and the other for odd-numbered gears—to enable quick and smooth gear changes without interrupting the power flow.
In a DCT motorbike transmission, the system consists of two input shafts, each connected to a separate clutch. One input shaft controls the odd-numbered gears (1st, 3rd, 5th, etc.), while the other handles the even-numbered gears (2nd, 4th, 6th, etc.). The two input shafts are connected to their respective gears and are constantly engaged with them. As a result, when a gear change is required, the transmission pre-selects the next gear on the alternate input shaft while the current gear is engaged.
During a gear change, one clutch disengages the current gear while the other clutch engages the pre-selected gear. This enables a seamless transition between gears without any loss of power or interruption in acceleration. The process is accomplished using a complex hydraulic and electronic control system that manages the clutches and gear selection based on the rider's input and the motorcycle's operating conditions.
What are the pros and cons of a DCT?
Dual-Clutch Transmission (DCT) offers several advantages. It can execute extremely fast shifts, surpassing the shifting speed achievable by a manual transmission operated by a rider. DCTs are particularly well-suited for high-power applications, which is why they can be found on powerful motorcycles such as the Honda Africa Twin and Rebel 1100. Another benefit of DCTs is the minimal driveline loss they experience, resulting in improved overall efficiency and power transfer.
However, Dual-Clutch Transmission (DCT) systems also have their drawbacks. They are highly complex systems that require meticulous fine-tuning, which can increase manufacturing and maintenance costs. If any issues arise with the DCT system, repairs can be quite expensive. Additionally, some riders have reported complaints about jerky throttle response at low speeds, often attributed to the computer-controlled clutch actuation in certain models.