“Continuously variable transmission” is possibly one of the most reviled terms in the automotive lexicon. The “CVT”, has become shorthand for “no fun”, and cars equipped as such are spurned by hardcore three-pedal enthusiasts and casuals alike. Is this actually a fair appraisal, or does the CVT deserve more respect?
After all, CVTs proliferate across the market. Once relegated to cut-rate, low-power compacts, CVTs have recently found their way into high-power full-size sedans and SUVs. Even sport compacts like the Subaru WRX use continuously-variable designs in place of traditional automatics, and a glut of hybrid cars have birthed the so-called “e-CVT” —a transmission that blends both the electric and gas drivetrains into one output shaft with infinitely variable gear ratios. Whether enthusiasts like it or not, the CVT is here to stay.
Belt And Road Initiative
To understand how CVTs became so reviled, we must understand how they’re different from a traditional automatic transmission. In a traditional automatic, hydraulic pressure is used to actuate gear changes; in a CVT, there are no gears at all.
Most CVTs use two pulleys connected by a belt to send power from the engine to the wheels. One pulley is connected by a spline and a clutch to the engine’s crankshaft. That’s the CVT’s input pulley (also called the drive pulley). A second pulley, connected to the drive pulley via belt, sends power to the driveshaft or wheels. That’s the output (or driven) pulley.
One or both of the pulleys are made up of a pair of cones, the tips of each facing one another to form the center of the pulley in the channel where the cone tips meet. The cones are hydraulically controlled, pushed together or pulled apart from one another depending on driving conditions.
At low speeds, the two cones that make up the driven pulley are spread as far apart as possible, allowing the belt that connects both to sit at the pulley’s narrowest diameter on the drive side. In this state, the input shaft spins rapidly relative to the output shaft, maximizing torque at the wheels. This position mimics first gear in a conventional automatic transmission, creating a gear ratio that maximizes low-end grunt.
Here’s a wonderful video that illustrates the concept:
As the car accelerates, the CVT’s input pulley cones are slowly coupled, bringing the tips of the cones together, and forcing the belt up the wall of the cones. This makes the effective diameter of the pulley larger.
The drive pulley then spins much more slowly relative to the driven pulley. This is equivalent to an overdrive gear in a traditional transmission, which maximizes top speed at the wheels from low engine rpm. In a modern car, both pulleys are made from cones, to allow for much more variability in gear ratios (and a wider range of feasible speeds).
From The Dutch To Your Driveway
If this sounds like a simple concept, it is. CVTs have been around since the dawn of the automobile; the Benz Patent Motorwagen featured a rudimentary belt-and-pulley CVT. The first commercially available car with a CVT would come from Britain, courtesy of Clyno, in 1923. (Clyno was a nickname derived from “inclined,” a reference to the CVTs’ inclined pulleys.)
These early CVTs could handle only modest power; most of Clyno’s successes came in the form of two- to five-horsepower motorcycles. Clyno, unfortunately, went bankrupt early in the Great Depression, before it could make many CVT-equipped cars, and ended its days as a footnote in automotive history.
It would take a few more decades for the first commercially successful CVT to arrive. In 1958, DAF (better known today by most Americans for its Dakar trucks) released the 600 city car, offered with what it called the “Variomatic” transmission.
The Variomatic was a rudimentary CVT integrated into the rear axle. It used massive pulleys, and rubber belts which stretched over time (although the 22-horsepower 590cc aircooled DAF engine was luckily low-stress). The 600 became a massive success in Europe thanks to its stellar fuel efficiency and compact footprint. DAFs with Variomatic transmissions were even sold briefly in America in the 60’s. They were eventually banned from American roads thanks to an idiosyncrasy of the Variomatic itself — early DAFs had no Park gear, just Drive, Neutral, and Reverse. The US government deemed this unsafe and stopped sales.
(Another Variomatic idiosyncrasy was that, since the reverse gear used the same pulleys as the drive gear, the DAF could do its top speed — around 75 MPH — backward. This led to groundbreaking innovations in Dutch racing.)
After DAF disappeared Americans wouldn’t get another CVT until the Subaru Justy in 1989. That modernized transmission — with a more traditional reverse gear and “Park” present — opened the floodgates for CVTs. Thanks to computer-aided design and advancements in material science, these CVTs could handle vastly more power without significant belt degradation. (Some modern CVTs even use steel chains between their pulleys, rather than belts, which increases longevity.) By the early 2000s, Honda, Nissan, Subaru, and Toyota all built CVT cars.
Rubber Band Transmission (Good or Bad, Depending On Intonation)
The reason automakers love CVTs — especially in economy cars, such as the frugal 66-hp Justy — is twofold. They have fewer moving parts than a traditional automatic, which makes them cheaper to manufacture. And they’re more fuel efficient. Because the gear ratio is infinitely and constantly variable, a CVT always keeps an engine at its most efficient RPM. Anyone who’s ever driven a CVT-equipped car is likely familiar with what this feels like.
Revs jump under hard acceleration, as the transmission’s input pulley allows the motor to spin at the RPM where it produces peak torque (usually, somewhere close to redline). Revs “hang” there as the vehicle’s speed increases. As vehicle speed climbs, the CVT’s input and output pulleys adjust to keep the engine in its sweet spot.
When cruising speed is reached, and throttle is reduced, the input shaft pulley expands and the output shaft pulley contracts, lowering engine speed for efficient operation. This is done smoothly, without a pause to shift as with a traditional transmission. Adding mild amounts of throttle is countered with pulley size adjustment to keep engine RPMs level. This is excellent for fuel economy.
While early CVTs lost some of this efficiency to high friction and heat, modern CVTs are much more advanced. According to Jatco, a transmission manufacturer that frequently partners with large Japanese OEMs, some of its recent CVTs have surpassed “the 90% transmission efficiency barrier, a feat considered very difficult for CVTs.” This is opposed to 85% power transfer efficiency on older torque-converter automatics.
Even race cars have gotten in on CVTs — the SCCA’s Formula 500 spec open-wheel series allows them, and in the 90's, Formula 1 preemptively banned the CVT entirely out of fear cars equipped would be too dominant and easy to drive. So why don’t enthusiasts like them?
Check Out How Annoying I Can Sound
This video might help explain why CVTs aren’t favored by enthusiasts. CVTs, by design, hold engine speed at near constant revs under acceleration. While this is technically more efficient, it leads to a droning engine sound and removes some of the sensation of speed caused by changing gears. Subjectively, this makes the car less engaging to drive. It sounds awful, turning melodic drivetrains into one-note wonders. Anecdotally, even my mother — a midwestern soccer mom who cares more about cupholders than cubic inches — grew to hate how her CVT-equipped Subaru sounded. She found the constant drone grating, and I can’t disagree with her.
Some manufacturers program CVTs to have “shift points.” Instead of smoothly changing the relative diameters of the input and output shafts for maximum power or efficiency, the diameters stay fixed to redline, and then change simultaneously to drop RPMs.
The action simulates the gears of a traditional automatic; In some cars, such as the new WRX, this even allows drivers to use paddles on the steering wheel to “shift” between gears. With this strategy, manufacturers still have the benefits of CVTs — the ability to change gear ratios on the fly, and lower build costs — without the transmission sucking life force and joy from enthusiasts’ veins.
What About E-CVTs (Which Aren’t Actually CVTs)
So what about cars such as the Lexus LC 500h, that blend electric and gasoline power into a single “e-CVT” gearbox? Those are an entirely different system than traditional CVTs. Instead of the cone-and-belt system, e-CVTs use a planetary gear set that integrates engine power with a pair of electric motor-generators. The specifics of this are complicated (and better explained visually in the 40-minute video above), but what’s important is that similar to a conventional CVT, the e-CVT allows for the engine to run at optimal RPM for either pure power output (under high load) or to charge the battery. Gear ratios can effectively be chosen at will, and the traditional rubber-banding sound of a CVT is still present.
While enthusiasts might not be thrilled that the future likely includes a lot more droning engines, there might be alternative options: some hybrids have done away with transmissions entirely. Koenigsegg’s direct-drive system, first implemented in the Regera, outputs engine power either directly to generators to recharge the battery or to the pavement. Most EVs have simple single-speed reduction gears to effectively serve as transmissions, as well, which means that the era of the CVT may soon come to a close… along with the era of the multi-speed transmission entirely.
