CVT vs. Automatic Transmission: Your Burning Questions Answered
What is a continuously variable transmission? Is it better to drive, more reliable, more efficient, or better than an automatic?
The automatic transmission as Americans know it today has been around and undergoing continual improvement since 1939. And while the concept of the continuously variable transmission (CVT) was patented in 1879 for use in sawmills and was employed in a handful of early lightweight cyclecars and a few oddball cars in Europe decades ago, Americans really got their first taste of the concept in the 1987 Subaru Justy. Modern CVTs have sold themselves primarily as a more efficient alternative to the automatic transmission. It helps that they also happen to be inherently smooth in their operation. Is this relative newcomer ready for primetime, and worthy of consideration in your next new vehicle?
How Does an Automatic Transmission Work?
A modern automatic transmission uses one or more sets of epicyclic or planetary gears (consisting of a sun, planets, and a ring gear) to achieve many different (typically between two and ten) gear ratios. These gears always remain in contact with each other, so there’s never any chance for “grinding a gear” when changing ratios, as happens when a novice shifts a manual “sliding gear” transmission. Hydraulic pressure operates various bands and/or clutches that stop or lock one of these planetary gear elements to change ratios, as controlled by a powertrain computer.
How Does a CVT Work?
The mainstream CVT concept most Americans have access to features a system of two variable pulleys connected by a steel belt or chain. One half of each pulley can be moved closer or farther away from the other, thereby changing its diameter. This changes the ratio, in much the same way as shifting a 10-speed bike’sbicycle’s front and rear derailleurs does, only here there are no steps—the ratio can be changed continuously, between fixed high and low ratios determined by the size range of the pulleys.
Which Is Stronger, CVT or Automatic?
Because an automatic gearbox transmits its torque entirely via metal gear teeth that are always in contact, this design can be scaled up to reliably handle extremely high torque loads—think Challenger Demon or Ford F-550 diesel (which can produce as much as 950 lb-ft).
In a belt or chain-type CVT, torque must be transmitted by clamping the sides of the pulleys together hard enough to either push the steel elements of the belt or pull the pins of the chain from one to the other via friction. For this reason, this design’s functional upper limit on torque capacity seems to be about 300 lb-ft (Infiniti’s 2.0-liter turbo applications in the QX50 and QX55 make 280 lb-ft, while the 2.4-liter turbo powering the Subaru Ascent, Legacy, Outback, etc. makes 277 lb-ft).
Note that other CVT designs, like Nissan’s Extroid toroidal CVT promise to deliver greater torque, but the traction fluids they require don’t work at the extremes of temperature we see in North America.
Which Is More Efficient, CVT or Automatic?
Lower gear ratios offer strong torque multiplication for quick acceleration from a stop, while higher ratios help slow the engine down at highway speeds to save fuel. Having more ratios to work with in between these extremes allows the engine to work most efficiently when cruising at different middle-range speeds.
With an infinite number of “speeds” available, CVTs promise greater efficiency by allowing the engine to spend more time operating in its efficiency “sweet spot.” They can also help keep the engine operating right at the rpm where it produces peak power when accelerating, helping make the absolute most of a small engine’s available power.
But note that advances in automatic transmission technology are allowing these gearboxes to match the overall ratio spread, and with so many ratios to choose between those extremes, the CVT’s advantage is shrinking.
What are the Pros and Cons of CVT Transmissions?
Pros
- Can help an engine run more efficiently
- Optimizes acceleration performance
- Sometimes smaller and often lighter than a comparable 9- or 10-speed automatic
- Extremely smooth operation, with no “gears” to shift
Cons
- CVTs generally feel less sporty/engaging to drive
- “Motorboating”—floor the throttle, and the engine may race to the power peak and stay there as the vehicle accelerates (some customers erroneously report this to dealers as “slipping”)
- Cost—not at purchase, but having fewer mechanics certified to service CVTs than automatics elevates repair costs
- Requires special CVT fluid, with potential for catastrophic maintenance error
What are the Pros and Cons of Automatic Transmissions?
Pros
- Technology is very mature, so potentially fewer problems and easier/cheaper repairs
- Recent compound gearset designs provide such a wide spread of closely spaced ratios that planetary transmissions can closely approximate CVT efficiency
- More engaging to drive, particularly when programmable for harder or softer shifting
- Less potential for damage due to vehicle or towing overload
Cons
- Gear shifts not always imperceptibly smooth
- Weight and complexity (typically more moving parts)
- Slightly greater fuel use/CO2 emissions
Do CVT Transmissions Last as Long as Automatic Transmissions?
There are far fewer CVTs on the road than regular automatics, and the technology is way less mature, so several early CVT applications have experienced higher-than-average problems and failure rates. Nissan vehicles with JATCO CVTs are a case in point. If considering a new vehicle with a CVT, maybe lease it, or budget for more aggressive maintenance (increase the frequency recommended for transmission fluid changes)—and think twice about scaling the Rockies with it fully loaded (overheating is particularly hard on a CVT). If considering a used vehicle, check its CarFax and scan owner forums to gauge the model’s track record.
Can You Drive a CVT Like an Automatic?
Many modern CVTs offer standard or selectable programming that apes the gearing of a regular automatic transmission. This eliminates customer complaints of “motorboating” or slipping, and improves engagement, but it also erodes the transmission’s efficiency advantage. Often these models include shift paddles or a “manumatic gate” on the transmission shifter that allows shifting up or down one simulated gear at a time.
What About Hybrid eCVTs?
Little of the above CVT discussion applies to Toyota vehicles featuring Hybrid Synergy Drive (Corolla, Prius, Camry, RAV4, etc.) nor to the Ford Hybrids that licensed this technology (Escape, Maverick, et. al.). These use a single, robust planetary gearset, with the engine connected to the planet carrier, and electric motor/generators connected to the sun and ring gears. This design has demonstrated exceptional efficiency and proven incredibly robust in extended taxi and livery service, though once again the engine revolutions seldom track accelerator position.
Which is Better, CVT or Automatic?
If efficiency is your ultimate goal and you’ve already decided on a smaller, lighter vehicle with a 2.0-liter or smaller engine, a CVT will optimize the performance when merging onto a highway, and then promise to give you the best efficiency while cruising on that highway. For larger vehicles that you plan on burdening with a full complement of passengers and gear for summer vacations, or for drivers with sportier ambitions, consider a traditional automatic—or even a third option, the twin-clutch automatic or dual-clutch transmission (DCT) as found on some Hyundai, /Kia, Porsche, and /Audi vehicles, as well as (PDK), the new Corvette, and among others.
What Vehicles Offer a CVT?
Here is a partial list as of publication:
- Mitsubishi: Eclipse Cross, Mirage, Mirage G4, Outlander, Outlander Sport
- Toyota: Corolla, Corolla Cross, Corolla Hatchback
I started critiquing cars at age 5 by bumming rides home from church in other parishioners’ new cars. At 16 I started running parts for an Oldsmobile dealership and got hooked on the car biz. Engineering seemed the best way to make a living in it, so with two mechanical engineering degrees I joined Chrysler to work on the Neon, LH cars, and 2nd-gen minivans. Then a friend mentioned an opening for a technical editor at another car magazine, and I did the car-biz equivalent of running off to join the circus. I loved that job too until the phone rang again with what turned out to be an even better opportunity with Motor Trend. It’s nearly impossible to imagine an even better job, but I still answer the phone…
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