The SMG 2 automated manual transmission on the BMW M3 E46
Automotive technology is constantly evolving to offer drivers increasingly sophisticated and enjoyable driving experiences. Among the innovations that have marked automotive history, the Sequential Manual Gearbox (SMG) holds a prominent place. Developed by BMW in collaboration with Getrag and Sachs, the SMG was one of the first automated manual transmissions with paddle shifters, now used in most high-performance cars.
In this article, we'll delve into the depths of the SMG sequential gearbox, exploring its operation, history, advantages and disadvantages, and its impact on the driving experience. From the underlying technology to on-road performance, we'll examine every aspect of this iconic innovation, providing car enthusiasts with a comprehensive understanding of one of the most remarkable advancements in the modern automotive industry. Prepare to experience the power and precision of the SMG sequential gearbox in all its glory.
Preamble
First, it's important to note that the SMG system isn't a torque converter automatic transmission with manual shift capability—like BMW's Steptronic or Porsche's Tiptronic. It's a manual transmission with a clutch, but without a clutch pedal, that can shift gears automatically in response to driver input. BMW developed the SMG in close collaboration with Getrag and Sachs, and used similar technology in the Williams BMW Formula 1 race cars.
The SMG sequential gearbox is essentially a six-speed manual transmission where the clutch and gears are electro-hydraulically actuated by a computer in response to pressure applied by the driver to two paddles behind the steering wheel, or by pushing a gear lever forward or backward. There is no clutch pedal . Furthermore, the SMG can operate in fully automatic mode if desired.
After getting into the car, you'll see an orange LCD screen in the instrument cluster that indicates the gear or mode you're in. ' R ' is for Reverse, ' 0 ' is for Neutral, ' A ' is for Automatic, and ' S ' is for Sequential. This display is not only small, but it can also be confusing because Automatic mode includes both an 'A' and an 'S' symbol, while Sequential/Manual mode has an 'A' in a different font. Similarly, we're more accustomed to using 'N' instead of '0' for Neutral. It can sometimes take a while to figure out which mode the transmission is in.
The system also includes a " DriveLogic " button just behind the gear lever which allows the driver to adjust the speed of gear changes and shift points using six different settings.
The SMG gearbox on a BMW M3 E46
To start a BMW M3 E46 SMG 2 , your foot must be on the brake and the gear selector in the '0' position with the ignition on. Turn the key, and the 343-horsepower, 3.2-liter inline six-cylinder engine roars to life, emitting a deep rumble from the M3's four exhaust outlets. The SMG can be switched from manual to automatic mode at any time while the car is running; simply push the gear selector to the right. Pushing it to the left engages neutral.
Just behind the steering wheel are two paddle shifters that can be reached with your fingertips. To shift up, the driver pulls the right paddle '+', and to shift down, they pull the left paddle (-). The driver can also shift up by pulling back on the floor-mounted gear lever, or down by pushing it forward. (This is the opposite of how some semi-automatic transmissions work.)
The SMG DriveLogic system has six settings: the lowest setting shifts gears earlier and more easily into sixth gear to save fuel; the highest setting revs the engine higher before shifting and tends to stay in lower gears to keep the engine revving faster for greater responsiveness. It is also more aggressive during downshifts.
The SMG II experience
Let's talk about automatic mode first. When driving in the city, it can be easier to let the transmission shift gears automatically in this type of driving environment, even though there's no clutch pedal. Under moderate acceleration in automatic mode, with the lowest DriveLogic setting, the transmission shifts gears at around 2,500 rpm, and it does so slowly—even more slowly than with a normal manual transmission. At the same rate of acceleration, but with a higher DriveLogic setting, the transmission shifts more quickly at higher engine speeds, typically around 3,500 rpm. If you really push it, the shift points are even higher. When you slow down or coast downhill, the SMG automatically downshifts, and when you brake, the downshifts become more aggressive.
Compared to a conventional automatic transmission, the SMG is more performance-oriented, but depending on the DriveLogic setting and your driving style, gear changes are generally not as smooth . As a result, jerkiness can be felt when driving at moderate speeds.
In manual mode , things get more exciting. Under hard acceleration, with the DriveLogic setting at its maximum, gear changes are significantly faster than with a standard manual transmission. BMW claims the fastest gear changes take only 80 milliseconds and are aggressive enough to shake the rear of the vehicle.
Moreover, if the driver selects the highest DriveLogic setting and deactivates DSC (Dynamic Stability Control), the SMG's shift times "correspond to the sporty performance of a true racing car," according to BMW comments at the time.
The downshift speed using the paddles also varies depending on the DriveLogic setting: gear changes are smoother when DriveLogic is set low, and faster when it's set high. Most surprisingly, the SMG system performs its own double-clutching —that is, it blips the throttle to match engine speed to transmission speed for smoother gear changes—during downshifts. And it does this much faster than a driver could achieve manually with a standard manual transmission.
A supposedly safer driving experience
The ability to keep both hands on the steering wheel is a definite advantage of the SMG system, as it allows for better steering control. However, in certain situations, it's difficult to keep both hands on the wheel while shifting gears with the paddles. When accelerating from a standstill and turning at more than 90 degrees, it's necessary to shift into second gear before the end of the turn, and it's difficult to reach the paddle with your right hand at such a sharp steering angle. The same applies when negotiating tight corners where gear changes are required. In these situations, I found myself using the floor-mounted shifter.
Because the SMG is very similar to a manual transmission, the car tends to roll backward when starting on an incline. To prevent this, a special function called "hill climb assist" can be engaged in manual or automatic mode for forward or reverse. The driver simply presses the brake pedal and pulls the paddle briefly. When the brake is released again, the M3 is ready to move forward in two seconds without rolling backward.
The SMG has several safety features: if you slow to a stop without downshifting, the SMG will automatically downshift to first or second gear. However, if you forget to upshift while accelerating, the SMG will not automatically shift to the next gear (unlike many automatic/manual transmissions such as Tiptronic). It will, however, prevent you from over-revving and damaging your very expensive engine.
Should you buy a BMW equipped with an SMG 2 gearbox?
Ultimately, our opinion of the SMG system is rather mixed. In normal use in its automatic mode, the driver experiences much slower and less pleasant gear changes than with a manual or torque converter automatic transmission. As a driver, it's difficult to understand the marketing arguments for this Formula 1-inspired technology, which was nevertheless ahead of its time.
The SMG transmission truly shines in sportier driving and its most aggressive modes (from gear 4 to 5 onwards). In these conditions, gear changes are quick and crisp, and downshifts are exhilarating, with blips of the throttle highlighting the delightful sound of the BMW inline-six engine. The driver then becomes a racer, fully focused on the road. It's only at this point that the marketing claims of the time for this gearbox truly make sense.
The SMG is therefore a reflection of the robotic transmissions of the early 2000s : not very pleasant on a daily basis with very long shift times and giving jerks, but making full sense in manual mode when the driving pace becomes higher.
In 2022, this type of transmission is therefore rather unpleasant in the city, especially when compared to automatic transmissions with torque converters or dual-clutch gearboxes. However, they offer a raw, "racing" feel during sporty driving that is no longer found today, as manufacturers have made significant efforts to smooth out gear changes, at the expense of the driving experience. In this context, even though my preference for BMW remains the manual gearbox, the SMG is still a viable alternative, especially for a fun car intended for limited city driving .
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