Manual transmission or automatic? It’s a direct mechanical connection or convenience and ease. Is shifting gears a thrill or a hassle? In the United States, automatics have sold better than manual transmissions since at least the 1970s, and by 2007 automatics outsold manuals for the first time worldwide. While manual transmissions have become a bit better over the years, automatics have become much, much better. The once clear efficiency and cost advantages of manual transmissions are gone. And there are now different types of automatics too. Which automatic works best for you? Traditional automatic, dual-clutch, continuously variable or automated manual? Understanding those terms – and their advantages and disadvantages – can be confusing. And how many gears are enough gears? More about all that below.
The Manual Transmission Lives. Barely.
Today only about two-percent of the new cars sold in the United States are equipped with manual transmissions. All new Ferraris, for example, are automatics and BMW no longer offers its 3-Series sedan with a manual. Kia’s cheapest car, the Rio LX sedan, comes standard with a six-speed automatic. Most new cars are automatic only. But stick shifts are cool. And two-percent of 17.3-million total vehicle sales in the United States is 346,000 cars and truck. Beyond that a few performance cars – Mazda MX-5 Miata, Ford Mustang GT350, and Honda Civic Type-R to name three – almost need a manual transmission. The subject here is vehicles with internal combustion engines. Electric cars don’t need the variable gearing and hybrid systems are so complex that explaining them may cause cause many readers’ brains to explode.
Why Transmissions Exist
Internal combustion engines don’t make the same amount of torque all the time – that’s twisting force and the amount of work that can be done with each engine revolution. At low engine speeds torque is low and there’s not enough to move the vehicle. Then as engine speed grows, the torque output grows until it peaks. After that peak, the engine keeps spinning but torque production trails off. So, internal combustion engines need to operate in this narrow, torquey sweet spot – generally between about 1500 and 4500 rpm for every day piston engines – to be efficient. The variable ratio gear sets inside a transmission keep the engine in that sweet spot when the vehicle itself is moving at different speeds. Plus, well, a reverse gear is a necessity too. Electric motors, on the other hand, make the same amount of torque no matter how fast they are whirring along. And electric motors can run in reverse. So, they don’t need more than one forward gear.
Manual Transmissions
With a manual transmission the driver decides what gear is the right one to be in. It means depressing a pedal to operate clutch plates that disengage the engine, moving a mechanical lever to select the next gear, and then releasing the pedal to bring the plates back together and move the vehicle.
In most ways, today’s manual transmissions aren’t much different than those used 100 years ago. And it is a direct connection between driver and vehicle. That in mind, through history most manual transmissions have been terrible. The clutches have needed leg-cracking effort to work, the shift levers have been poorly positioned, and actually getting into the next gear was often a matter of pure luck. Old cars with manual transmissions were, usually, awful. But when a manual transmission works well, it’s awesome. The driver feels the engine’s rise and fall and the torque can be felt rising up through the shifter into their palm. And today’s manual transmissions are pretty good with up to seven forward gears. And compared to the manuals of the 1980s and 1990s, they’re awesome.
Conventional Automatic Transmissions
Exactly who came up with the automatic transmission is disputed. But it was in 1939 that General Motors introduced its “Hydramatic” transmissions for the 1940 Oldsmobiles and Cadillacs. The “hydra” part of that GM brand name refers to the hydraulic operation of the transmission. Early automatic transmissions relied solely on hydraulic fluid to control the switch between gears, and the fluid coupling of a torque converter to keep the engine from stalling every time the vehicle stops. In a real sense, an old school automatic transmission is a hydraulic computer. How the fluid in a transmission flows through the different maze-like passages in a “valve body” metal casting is how the transmission “knows” when to shift from one gear to another. No part of any car or truck is more complex than an automatic transmission. While electronic controls now coordinate the operation of most conventional automatic transmissions, hydraulic pressure is still there to shove the gears around. Many automatic transmissions can now be manually controlled using either a traditional shifter or paddle triggers behind the steering wheel. These provide a level of control during, ahem, “spirited” driving. But it’s not always a satisfying alternative to a manual transmission. And virtually always, the computer will cut in and shift if there’s a risk of mechanical damage.
How Many Gears Is Enough?
Early automatic transmissions like Chevrolet’s “Powerglide” had only two forward gears. Today’s automatics have between five and ten different ratios in their aluminum cases. The point of increasing the number of gears is to always have a gear available for the engine to operate most efficiently in given any situation. In the 10-speed automatic installed in the Ford F-150 Raptor, for instance, that means first gear is a 4.69:1 ratio while second through seventh gears are tightly spaced between 2.98:1 and a “direct drive” 1:1. Eighth, ninth and tenth gears are all “overdrives” between 0.85:1 and 0.63:1 that keep engine speeds low while the vehicle is cruising and the need for torque is minimal. Automatic transmissions have improved in every way. For example:
- 2019 Ford Mustang with the 310-horsepower, 2.3-liter, turbocharged “EcoBoost” four-cylinder engine.
When mated to a six-speed manual transmission, it is EPA-rated at 21 mpg in the city, 31 mpg on the highway and 25 mpg combined. The same Mustang with the same engine and the optional 10-speed automatic, is rated at 21 mpg in the city, 32 mpg on the highway and 25 mpg combined.
- 2019 Hyundai Elantra is offered with six-speed automatic or six-speed manual transmissions.
The manual is EPA-rated at 26 mpg in the city, 36 mpg on the highway or 29 mpg combined. Go for the automatic and those numbers climb to 28 mpg city, 37 mpg highway and 32 mpg combined. That’s simply a transmission that works really well – at least in EPA testing.
Produced by the German company ZF, the 8HP conventional, torque converter-equipped eight-speed automatic transmission is used by Audi, Aston Martin, BMW, Hyundai’s Genesis division, Jeep, Ram, Jaguar, Land Rover, and even Rolls-Royce, among others. The 8HP can be tuned for responsiveness in a performance car or virtually undetectable operation in a luxury vehicle. All other things being equal, engineers would always want more gears. But for the moment, based on the 8HP’s ubiquity, eight is enough.
Continuously Variable Transmissions (CVT)
Continuously variable transmissions are simple and cheap to produce. However, they also can produce a droning sound during acceleration. The theory behind the CVT is simple. A belt or chain of length is strung between two paired sets of cone-shaped spools on shafts. As the cones move in and out with the engine’s torque loading, the ratio between the two shafts gradually changes. That’s the “continuously variable” part of the name. Because the movement of the belt or chain on the spools is determined by torque load, during acceleration the engine gets to its torque peak and stays there. That’s the drone often heard with CVT equipped vehicles.Manufacturers have used various strategies to fight the CVT drone. Some, like Nissan which uses CVTs extensively, have developed computer determined, stepped control of the spools that results in “virtual gears” that many find less tiresome. Toyota, on its new Corolla models, combines a gear low ratio “first” that transitions as speed builds to a CVT, allowing a perkier initial acceleration. CVTs work best with the turbocharged engines as in the current Honda Accord, because their torque production minimizes the amount of ratio change necessary.
Dual Clutch Transmissions
The dual clutch transmission (DCT) is, basically, two manual transmissions in one box controlled by a computer. It’s called a dual-clutch because there’s one clutch for the even numbered gears and another clutch for the odd gears. During automated operation, the computer engages the clutch for one gearset and disengages it from the other to perform the shifts. Because the inactive gearset is always prepped to go, the shifts can be lightning quick. So dual-clutch transmissions are often found in high-performance cars like Porsches.
DCTs can also be shifted manually and often more quickly than traditional manual transmissions. For instance, Porsche claimed that its 2017 911 GT3 model equipped with a DCT (marketed as the PDK for “Porsche Doppelkupplung”) would go from 0 to 100 kph (62 mph) in 3.4-seconds while it took a manual equipped car 3.9-seconds to do the same trick. And DCTs can be very effective when shifted manually using paddle triggers. DCTs are, however, complex, and are not cheap to produce. When they fail, fixing them can be expensive. So as conventional automatics with torque converters have become better (and the ability to shift them manually has improved) some manufacturers have been moving away from DCTs. For instance, BMW used a seven-speed DCT on the 20XX to 2016 M5 hyper-sport sedan, but fit a version of the ZF 8HP conventional automatic to the current M5.
Automated Manual Transmission
An automated manual transmission is literally a clutched manual transmission that’s designed to be operated by a computer. Many manufacturers have attempted automated manual transmissions over the years, but the most notorious is Ferrari that offered it’s “F1-Superfast” six-speed automated manual beginning with the 1997 version of the mid-engine F355. The system remained in use with that car’s successors, the 360 and F430. But when the 2010 458 Italia was introduced, Ferrari adopted a dual clutch system. If you’re shopping for a used Ferrari, try and find one with a manual transmission. Manual vs. automatic is still a debate now. But one more victory for the automatic occurred on July 18, 2019 when Chevrolet introduced its radical new, mid-engine 2020 Corvette. It’s only available with a dual clutch automatic. The manual vs. automatic debate is almost over.