How does a sequential gearbox work?
Most of us are familiar with standard automatic or manual transmissions. With most automatics, you simply put the car into drive, and the transmission does the rest for you. Traditional manuals require you to move through the gears in an “H” pattern, starting with first gear at the top left and usually ending with either reverse or sixth gear on the bottom right.
However, there is another form of manual transmission known as a sequential gearbox. It is similar to a manual transmission in that you still need to move through the gears yourself, but rather than choosing a gear from the H layout, you simply hit a lever up or down to move through the gears.
Benefits of a sequential gearbox
Sequential gearboxes are faster and easier to use than normal manual gearboxes. There is no need to remember the position of each gear, as you only have to move the gear lever up or down in the direction you want to shift. This speed of use makes sequential transmissions common in high-performance vehicles and race cars. They are also used in motorbikes.
Another benefit of a sequential gearbox is that it is impossible to skip gears, which can damage your transmission or prematurely wear out your clutch if it is not done correctly. When racing, gear change errors at speed can cause lockups and engine failure due to over-revving.
Many race cars have sequential transmission paddles mounted on the steering wheel – left to downshift and right to upshift – enabling you to keep your hands on the wheel for greater steering control.
Disadvantages of a sequential gearbox
One major drawback of a sequential gearbox is the cost – they are much more expensive than a standard transmission. Sequential gearboxes are not particularly practical for urban driving because they tend to be clunky at low speeds and don’t allow you to skip gears. Also, due to the way they are constructed, they tend to be louder than other transmissions and require more frequent maintenance.
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Sequential Manual Gearbox in BMWs
A sequential Manual Gearbox (SMG) in a BMW is designed to provide fast, precise shifts without a traditional clutch pedal.
Key Features of BMW SMG:
- Electronically Actuated: Unlike a conventional manual gearbox, SMG uses an electro-hydraulic system to control the clutch and gear changes.
- Sequential Shifting: Gears must be changed in order (e.g., 1-2-3-4-5-6, not skipping gears like a traditional manual).
- Paddle Shifters or Gear Lever: Drivers can shift gears using paddles behind the steering wheel or by nudging the gear lever forward/backwards.
- No Clutch Pedal: The system automatically operates the clutch, offering a manual-like experience without clutch engagement.
- Automatic Mode: Some SMG models allow for fully automatic operation, behaving like a standard automatic transmission.
BMW Models with SMG:
BMW E46 M3 (SMG-II) – One of the most well-known applications, providing quick shifts and track-ready performance.
BMW E60 M5 / E63 M6 (SMG-III) – Upgraded for high-performance V10 engines, but some drivers found it jerky in normal driving.
BMW E36 M3 (SMG-I) – The first iteration is less refined than later versions.