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Chilton Answers: What Should I Know About Manual vs. Automatic Transmissions?

Automatic transmission

By: Gary McCormick - originally published at

The last significant paradigm shift to occur in the world of automobiles was the post-WWII ascendancy of the automatic transmission. Automatic transmissions were first introduced in the late 1940s but didn’t come into widespread use until the 1960s. Now, as the second decade of the 21st-century draws to a close, only 20 percent of new vehicles even have a manual transmission option; only about two percent of all new cars sold in 2018 had a clutch pedal.

There are several different types of automatic transmissions, each with advantages and disadvantages, and a variety of reasons why automakers have gravitated toward their use.

Conventional Torque Converter Automatic

Conventional Automatic Transmission

Conventional automatics use a hydraulic torque converter to transfer engine power to planetary gear sets which permit the engine to operate in the proper rpm range. Shift points are calculated by the engine-management system – the car’s computer – based on input from sensors that monitor throttle position, vehicle speed, engine RPM, load, and other factors. Electrical and hydraulic actuators actually do the shifting.


Continuously Variable Transmissions

Continuously Variable Transmission

Continuously variable transmissions – CVTs – react to those same sensor inputs by controlling a pair of variable-diameter pulleys, one on the engine side and one on the transmission side. This arrangement allows virtually infinite drive ratios within the upper and lower operating limits of the transmission. In addition, by letting the “belt” (actually a type of chain) slip there is no need for a clutch or a torque converter.


Manual and Automated Manual Transmissions

Manual Transmission

Manual transmissions have a series of parallel gears that slide to engage when you press the clutch and move a lever. Automated manual transmissions, or the now rare semi-automatic, use sensors and actuators to operate the clutch and shifter, or just the clutch, of a manual transmission. This type attempts to combine the efficiency of a manual and convenience of an automatic, and most allow the driver to manually change gears, though the actual shifting is performed by the computerized systems. The most recent, and most sophisticated, version of this type of is the dual-clutch transmission. With this type, computer-controlled clutches and actuators to do all the messy work of clutch engagement and shifting, so there is no gap between gears, with one engaging seamlessly as the other disengages.

Why Carmakers Prefer Automatics

rush hour traffic

Far and away, the most common transmission today is the conventional torque-converter-equipped automatic. The standard, garden-variety slushbox is loved by auto manufacturers for one simple reason: it gives them a considerable measure of control over the manner in which your vehicle is operated.

The reason they want control is to make good on their promise to regulators that their vehicles will meet fuel mileage and emissions requirements. Control also makes it easier to predict and prevent warranty claims caused by driver behavior. By “mapping” a variety of performance-affecting conditions (such as engine RPM, vehicle speed, throttle position, engine temperature, air temperature, and more), the algorithms built into the vehicle’s engine-management system can determine the optimum time to shift, while simultaneously controlling other factors to keep the engine healthy and efficient.

That’s not to say that the electronic brain under the hood of your car has its way, all of the time. Jam your foot hard on the throttle, and the computer chip will read all the signs, and push the buttons to shift down into a lower gear, all the while preventing over revving, minimizing emissions output and maintaining fuel efficiency. Most conventional automatic units permit some degree of actual manual shifting as well.

CVT transmissions have gained favor for their simplicity and their efficiency; they have a lot less moving parts than a conventional automatic and better than 80% efficiency. However, they also have two downsides: Many drivers are turned off by the lack of “shifts” between gears and constant engine RPM, and they cannot handle high torque or heavy loads. To combat the first issue, many units now employ fake “gears” to mimic the feel and sound of a conventional transmission, and some even allow manual shifting between them.

However, even automated manuals and dual-clutch transmissions, which allow the driver the option of deciding when to shift, demand little of the vehicle operator in the way of physical skill and expertise. The car’s electronic brain and its minions – the valves and actuators that push and pull to move the gears in the gearbox and engage the clutch – are doing all the real work.

Why Enthusiasts Prefer Manuals

Audi rally car in a slide

For the stop-and-go traffic of the morning commute, or the slow grind of weekend beach traffic, an automatic transmission can be a godsend – but to feel the visceral joy of driving, enthusiasts prefer to take full control. When exercising years of finely honed skill to put a well-tuned car through its paces on a curving road, or race track, there is nothing better than rowing through the gears the old-fashioned way.

There is a range of other skills that come into play when driving for pleasure, and not just getting from point to point — gauging the proper speed to take a turn, exiting one curve set up on the proper line to enter the next, braking efficiently to carry your momentum through the corners. All these things are part of the suite of skills that a good driver must possess. Exercising those skills, even at moderate speeds, is what elevates driving a car above mere transportation.

But perhaps of all a driver’s skills, the proper, efficient use of a manual transmission is the one which elevates enthusiast driving above the point-and-go level of an automatic. Balancing vehicle speed against engine rpm and determining when to change up or down, matching revs with a blip of throttle, while braking or accelerating and executing a smooth clutch engagement so as not to upset the chassis, is an integral part of achieving that sublime feeling of being connected to the machine, and the road. There is a rhythm, an art, and a science to it – like ballet. It requires, and fosters, an understanding of physics and how your vehicle’s systems work together; it is a liberating analog pushback against the electronic uniformity that pervades modern life – and it’s just plain fun.