Introduction to Automatic Transmissions

One of the major choices you'll make when buying a car is choosing between an automatic transmission or a manual gearbox. The choice affects everything from the cost and reliability to the availability of the car. It can also impact how you drive every day and even what kind of driving licence you need. People can have strong opinions on the subject — some petrol-heads will insist that only a manual is good. Others only want to get from A to B and make sure that the car manages itself as much as possible.

The difference between manual and automatic transmissions

What is the difference?

Put simply, a car with an automatic transmission manages the linkage and gearing between the engine and the drive shaft, while with a manual, you have to select the gears yourself and work the gear change. Mechanically, a manual transmission is simpler and more robust than an automatic.

Manual technology has been in use since engines needed gears. A skilled driver can also get more out of a manual transmission than an automatic. So why would you choose an automatic?

Driving an automatic car

When you drive a car with an automatic transmission, you only have to focus your attention on steering, accelerating and braking. As with a manual, there is a gear lever, but the choices on it are limited to "drive," "reverse," "neutral", and "park". When you select "drive", the vehicle goes forward slowly, and you use the brake to control the speed until you switch to the accelerator. "Reverse" and "neutral" explain themselves, while in "park", the wheels are effectively locked by the transmission. More expensive cars have more options on the transmission, including the choices of several lower gear ratios and "overdrive" for sportier handling.

The automatic driving experience differs greatly from driving with a manual. You are balancing the accelerator and the clutch, finding the bite point when you start moving and coming off the accelerator when you change gears so that the engine change doesn't over-rev the vehicle. It is not impossible to stall an automatic, but it isn't easy, and some manoeuvres — like hill starts — are taken care of for you. It is much more relaxing to drive an automatic, especially in-town driving and handling traffic jams, plus beginner drivers find automatics much easier to learn.

The difference between driving the different types of transmission also means that while you can pass your driving test using an automatic in Ireland and the UK, your driving licence is limited. You also have to pass another test in a manual before you can drive one legally. Many people take the manual driving test first because you are then permitted to drive both types, and it takes a very short time to get used to driving an automatic.

Automatic gearboxes

The most common automatic transmissions are hydraulic systems that use a torque converter instead of a clutch. They rely on engine demand to force the system up and down each gear. The system usually has fewer gears than a manual transmission and is set up for cruising rather than rapid gear changes. It is less suitable for twisting roads and active driving than a manual or the more advanced kinds of automatic. The torque converter cannot be 100% efficient, which has led to overheating and higher fuel consumption than manual models in the past.

Another fully-mechanical system is CVT (Continuously Variable Transmission), a compact gearbox often fitted in smaller cars. It works by having two cone-shaped pulleys linked side-by-side to a drive belt. When you rev the engine, one cone moves and the other cone automatically adjusts so that the drive belt maintains tension. CVT systems are used in several modern cars, particularly in low-power applications, such as commuters. Honda uses this system in its Hybrid Synergy Drive (HSD) system fitted with the Prius and the Lexus IS300h. CVTs are fairly reliable, but the drive belt can wear and slip, which leads to the engine revving while the car fails to accelerate.

Dual-clutch transmissions (DCTs) use two clutches in the gearbox — one clutch for each odd and even gear. This layout allows the transmission to engage the next gear as the current one disengages, and it allows the system to change far more rapidly than a manual gearbox. The system is controlled by electronics, which is why the system was first developed for racing cars in the sixties and seventies. As electronics have become cheaper and smaller, DCTs have come into use in high-end cars since 2003 with the Volkswagen Golf R32 and performance cars, such as the Bugatti Veyron and Ferrari California.

Automated manual transmissions (AMTs) use electronic controls and actuators to operate the clutch and gearbox. They can be fully computer-controlled or operated by the driver with switches that are often mounted on the steering wheel. This system was again developed from the racing scene, where drivers needed manual control of the gears for performance, but the steering wheel control and electromechanical clutch increased the speed of gear changes. AMTs are a halfway option between automatic and manual systems, and they provide more driver engagement than an automatic while allowing for a more relaxed drive.

Automatic transmissions vs manual gearboxes

Car enthusiasts end to prefer manual gearboxes to automatic transmissions. The experience of working the clutch and choosing the gear is more active than with an automatic, and it gives more of a feeling of connection to the car and the road. Prior to developing electronic control systems, automatic transmissions could feel sluggish and underpowered, making them less popular with drivers. The technique of active driving, where you use your skills and experience as a driver to change gears, also gives you more fuel efficiency and power than you can achieve with automatics.

Automatic transmissions have historically been less efficient than manual systems. Older automatic vehicles with torque converters rely on engine power to shift gears. They divert power from the engine output and require higher torque to operate, reducing fuel efficiency. Automatics have previously been less reliable than manuals, as their design is more complex. They also rely on the hydraulics of the transmission fluid to transmit torque and operate the gears, not only to lubricate the system. Modern automatic transmissions with electronic engine management and advanced hydraulic design are reportedly just as reliable as manual systems.

Complex designs, lower fuel economy and higher maintenance requirements have resulted in fewer sold automatics units than manual options. With autos requiring more development, manual gearboxes are cheaper to produce. Most newer cars with electronic engine management systems can deliver better performance and fuel economy than an equivalent manual. However, concerning vehicle ranges, an automatic model will still cost you about £1,000 more than a manual or £1,500 for a DCT variant.

The performance characteristics of automatics and manual gearboxes will vary in different driving regimes. On twisting roads, the automatic will be sluggish and can also cause the car to yaw as the system enters and leaves the turn in a gear that is not optimal. However, the automatic can maintain power and torque on hills and at low speeds because the transmission is always engaged, unlike using a clutch. Additional options are available on many automatic gearboxes to mimic the performance of manuals. Examples include holding on longer to lower gears for more revs and power or limiting the range of gears to two or three. Some automatics come with more gears than manuals and use engine management systems to choose between them for power or efficiency, as directed by the driver.

Conclusion on automatic transmission

There is no doubt that a car with an automatic transmission is easier to drive than a manual car. An automatic transmission is a great choice if you are only concerned with commuting and getting from point A to B. In Ireland and the UK, they are still a less popular and more expensive option, and new drivers are still encouraged to pass their manual test to avoid being limited in options. If you are concerned with the driving experience and enjoy being allowed to work the car more directly, then automated manual transmissions are becoming available on less expensive cars. Automatic gearboxes are also being designed with more sporty performances and increased options to choose between the range of gears.

As electronics improve and are integrated into engine and power management systems, automatics are becoming a less expensive choice. At the moment, the additional price point is noticeable because they are not the standard in Ireland and the UK. But an automatic transmission is the only option on some hybrids and all-electric vehicles, so this will likely change.