Bob Elton
by Bob Elton
cvt rip

I can't figure out the appeal of the Continuously Variable Transmission (CVT). Currently featured in the new Ford 500 sedan, the transmission system consists of a pair of cones and a steel drive belt to transfer power. The CVT offers a continuous ratio change (similar to changing gear with a standard manual or automatic) by varying the diameter of the cones, without a step in ratios like a conventional automatic transmission. While conceptually simple, the actual hardware is tremendously complex and expensive. What's more, supporters' claim that the CVT increases economy and performance simply doesn't bear close scrutiny.

Proponents claim that the CVT offers superior mileage by providing a higher overdrive ratio than other transmissions. (Overdrive is another way of saying that the engine turns slower than the driveshaft, which is typical of all modern automatic transmissions.) In the case of the Ford 500's Ford/ZF unit, the overdrive ratio is .41:1. In other words, the engine turns 4/10s of a revolution for every turn of the driveshaft. That's considerably greater than the .69 overdrive ratio of the conventional automatic transmission on offer.

In theory. In practice, the Ford CVT's ratio is 5.41:1; which is a much lower final drive ratio compared to the same car with a conventional automatic. The result is an overall ratio of 2.2:1 in the CVT car vs. 2.3:1 in a car with an autobox. The overall relationship of engine speed to wheel speed is nearly identical.

At 70 mph, the tach needle would point to the same number, no matter which transmission was installed. When cruising down the expressway, the engines in both cars would be going the same speed, doing the same amount of work, and thus getting the same mileage. The comparison remains valid at any cruising speed over about 30, where the automatic transmission is in overdrive.

It's a similar situation for off-the-line acceleration. The CVT has much less torque multiplication, but a lower-geared final drive. The Ford uses a torque converter between the engine and the gearbox to further increase torque multiplication at launch. Since Ford uses torque converters with the same torque multiplication (effectively the same as a gear reduction), the overall ratio between the engine and the wheels is the same. With the same gear ratios, the cars will have the same acceleration, no more and no less.

The CVT's main claim to fame is that it keeps the engine at a constant speed, either the most efficient or the most powerful, while accelerating. In the days when engines had narrow power bands and peaked torque curves, this may have been more than a theoretical advantage. But today's engines have torque curves as flat as Kansas, and power curves to match. And today's automatic transmissions have five or six geared speeds, usually with only about 18-25% ratio differences between ratios. In other words, modern engines have essentially the same amount of power or torque over a relatively wide RPM range, and today's automatic transmissions have a narrow enough ratio spread between their gears to use all of the torque and power that the engine produces.

Every transmission suffers internal power losses, but internal losses in the CVT's hydraulic control system are higher than that of a conventional automatic transmission. The hydraulic control systems have to operate at higher pressures or flows, to squeeze the steel cones on steel belts, diverting more energy from the engine and leaving less to move the car. Since the CVT's torque converter is similar to the conventional transmission, internal efficiency of the CVT is lower. This hurts the CVT's ability to deliver the promised higher mileage.

The CVT also requires special, expensive fluid to withstand the heat and pressure demands, and scheduled oil changes. In fact, all things being equal, the CVT has no performance, economy or reliability advantages over a more conventional system. But this equation doesn't include ergonomic factors, which put the CVT at a distinct disadvantage.

It's clear that people aren't comfortable driving a car without transmission shift 'feel"; they like to know when their transmission is in "low gear" or 'high gear'. Obviously, a seamless CVT transmission doesn't transmit this kind of information. As a result of customer feedback, Audi felt compelled to programmed their CVT to have steps, just like a conventional automatic transmission. This made drivers feel better, but defeated the CVT's original purpose.

Of course, I'm not the only one who fails to see the rationale for a CVT. After having invested millions in new technology and a new plant, rumor has it that Ford is about to discontinue the CVT option from the 500, writing off their investment before the model year has properly begun. The move would be a hugely expensive about-face, but it's the right thing to do.

Join the conversation
  • Max So GM will be making TESLAS in the future. YEA They really shouldn’t be taking cues from Elon musk. Tesla is just about to be over.
  • Malcolm It's not that commenters attack Tesla, musk has brought it on the company. The delivery of the first semi was half loaded in 70 degree weather hauling potato chips for frito lay. No company underutilizes their loads like this. Musk shouted at the world "look at us". Freightliners e-cascads has been delivering loads for 6-8 months before Tesla delivered one semi. What commenters are asking "What's the actual usable range when in say Leadville when its blowing snow and -20F outside with a full trailer?
  • Funky D I despise Google for a whole host of reasons. So why on earth would I willing spend a large amount of $ on a car that will force Google spyware on me.The only connectivity to the world I will put up with is through my phone, which at least gives me the option of turning it off or disconnecting it from the car should I choose to.No CarPlay, no sale.
  • William I think it's important to understand the factors that made GM as big as it once was and would like to be today. Let's roll back to 1965, or even before that. GM was the biggest of the Big Three. It's main competition was Ford and Chrysler, as well as it's own 5 brands competing with themselves. The import competition was all but non existent. Volkswagen was the most popular imported cars at the time. So GM had its successful 5 brands, and very little competition compared to today's market. GM was big, huge in fact. It was diversified into many other lines of business, from trains to information data processing (EDS). Again GM was huge. But being huge didn't make it better. There are many examples of GM not building the best cars they could, it's no surprise that they were building cars to maximize their profits, not to be the best built cars on the road, the closest brand to achieve that status was Cadillac. Anyone who owned a Cadillac knew it could have been a much higher level of quality than it was. It had a higher level of engineering and design features compared to it's competition. But as my Godfather used to say "how good is good?" Being as good as your competitors, isn't being as good as you could be. So, today GM does not hold 50% of the automotive market as it once did, and because of a multitude of reasons it never will again. No matter how much it improves it's quality, market value and dealer network, based on competition alone it can't have a 50% market share again. It has only 3 of its original 5 brands, and there are too many strong competitors taking pieces of the market share. So that says it's playing in a different game, therfore there's a whole new normal to use as a baseline than before. GM has to continue downsizing to fit into today's market. It can still be big, but in a different game and scale. The new normal will never be the same scale it once was as compared to the now "worlds" automotive industry. Just like how the US railroad industry had to reinvent its self to meet the changing transportation industry, and IBM has had to reinvent its self to play in the ever changing Information Technology industry it finds it's self in. IBM was once the industry leader, now it has to scale it's self down to remain in the industry it created. GM is in the same place that the railroads, IBM and other big companies like AT&T and Standard Oil have found themselves in. It seems like being the industry leader is always followed by having to reinvent it's self to just remain viable. It's part of the business cycle. GM, it's time you accept your fate, not dead, but not huge either.
  • Tassos The Euro spec Taurus is the US spec Ford FUSION.Very few buyers care to see it here. FOrd has stopped making the Fusion long agoWake us when you have some interesting news to report.