Do a Google search on “analysis of slip in a continuously variable transmission”. There’s a ASME paper that describes the phenomenon
Can’t be much, otherwise mpgs would be poor.
Interesting.
High clamping force levels reduce the efficiency of the CVT. However, high clamping force levels are necessary to prevent slip between the belt and the pulleys. Efficiency is found to be highest for 1 to 2% slip depending on the ratio.
One or two percent slip is hardly noticeable to most people. What most people mistake for slip is the transmission lowering the gear ratio in response to the driver opening the throttle more.
Slip is not the only loss in a transmission.
Those metal belts can’t go around the sheaves without a little movement between the mating surfaces. The “push-belt” types also have friction in the thin bands holding the belt together. This is the reason the CVT’s never matched the original hype of greatly improved fuel economy.
Loss of efficiency is not my main concern. I’m worry that the belt and pulley will eventually grind itself to powdered metal due to the slip, which necessitates the a transmission rebuilt.
I know that clutches in a manual transmission, traditional or automated, slip as well. But their replacement is much less involving than replacing clutches, belts, and pulleys deep inside am automatic.
Same ,I,m not dissing the people that have real need ,what pxxxes me off ,is that some of these people can go places and do more then I can do ,viz; I dont consider them impaired ,some people seem to have made a cottage industry out of duplicating HP placards.
I worked with one retired Guy ,that had handicapped plates on his Ranger ,we couldnt figure out why ,we asked Him was it because of his deceased wife ? No,he said it was because He had his knees replaced in the past,He walked as well as the rest of us ,I always assumed you had this surgery done so you wouldnt be handicapped the rest of your life and there are others ,I spotted this one guy down a rocky gorge fishing one day who was on full disability,this was during a period when I could barely pick my left foot up(I said to myself ,dont think I could make it out of there ) so I am just saying it seems some people work the system.
I believe there are groups of people who are never even offered this opportunity who would benefit greatly from the advantages thereof .including the morbidly obese (sorry fellows despite first appearences some of these people cannot help their condition on their own ) and woman should automatically be issued a handicap permit during the last trimester of pregnancy and including the first 6 months after the babys arrival .
I know there is genuine need and I know there is genuine abuse .
I think the real reason CV transmissions fail to live up to the hype is because having the engine run at some ideal RPM is not as critical as many believe.
Look at the brake specific fuel consumption (engine efficiency) curves at the bottom of this chart. At half and full throttle, those curves are so flat that it’s hard to tell exactly where the peak is. But at quarter throttle, you see a rapid rise in brake specific fuel consumption as the RPM rises. Unfortunately, with the rather lowish top gear ratios found in many manual transmissions, that’s exactly where our engines are operating while cruising down the freeway.
So to get the best possible gas mileage out of such a car, one needs to find a hill and dale road, the upgrades put the engine in its brake specific fuel consumption sweet spot and then you can coast down the downgrades with the engine idling or even switched off.
All I know is that with my current car (15 forester with CVT) I get much better gas mileage (34 MPG summer, door to door) than I have ever gotten with previous cars (mostly jettas)
The only problem I see with the CVT is it’s reliability. If/When they lick that…I’m all for it. But as of yet…many manufacturers of CVT’s are have major reliability problems. It is main reason I bought my Highlander over the Pathfinder.
So to get the best possible gas mileage out of such a car, one needs to find a hill and dale road, the upgrades put the engine in its brake specific fuel consumption sweet spot and then you can coast down the downgrades with the engine idling or even switched off.
I’ve tried this with my Insight (CVT) and it kills MPG.
A 1 to 2% slip is not significant. Even geared transmission have that much slip between the gears as they mesh and unmesh. That is what eventually wears out the teeth in the gears.
One reason that gas mileage is a little disappointing in CVTs is that the shift points, or the program of engine RPM to load is set to high. I know my 14 Legacy allows the motor to run at a higher RPM than I would have chosen for acceleration and is too quick to go to a lower range at the slightest change in load or pedal position.
In 2015, they change the program for the CVT to lower the engine RPM. They also made it shift in increments to simulate a geared transmission. The second change is kinda defeats the potential advantage of the CVT, but the first change has resulted in an additional 3 MPG overall.
My brother in law just bought a 2015 Honda Accord with a CVT. It has two ranges for RPM. In the econo mode, it holds the engine RPM lower. He initially drove it in the normal mode for awhile, then put the transmission into the econo mode. It bumped his mileage by several MPGs, from around 30 to 34 on his daily drive.
Unlike a pulley type CVT, gears do not depend on the friction to transmit thrust. Whereas gears teeth are subjected to the force they are supposed to transmit as they slip, the cones and belt or chain are subjected to the load force divided by the coefficient of friction of a metal to metal contact, not to mention a layer of lubricating fluid in between. I’ll bet that if a manual, diy or automated, is shifted at low rpm like a CVT and is provided with a tall top gear, it would have better mileage than a CVT as the manual would have the lowest parasitic drag. 10 years ago, the civic hybrid was rated at 51 mpg with a stick while the CVT was 48mpg
Properly designed and lubricated helical gears transmit forces from one to the other with an absolute minimum of friction. Gear teeth surfaces (with the exception of worm gears) are designed to “roll” against one another rather than slip. Admittedly, none is perfect, but they’re pretty darned good. The only real relatively high-friction gears are worm gears and herringbone gears, and to some extent straight-cut gears (used in racing due to their greater strength, as the load is transmitted across the entire tooth simultaneously). And even these are designed for as low a friction as possible. None of these are used in any high rpm application in stock automobiles. But, Chunky, I know you well enough by now to know you’re a knowledgeable engineer and I’m perhaps venturing into a highly technical (and really meaningless to the thread) subject of debate. It is true that there is no gearset totally free of friction. It’s a fact of life. Sorry, I can’t help myself. 
The real alleged advantage of CVTs is their ability to maintain optimal (for the engine) gear ratios and their absence of losses during shifting. Note the use of the word “alleged”.
My reticence with CVTs is that they haven’t yet proven themselves to be expected to last the life of the car, which the overwhelming majority of do. And, I have to admit, I like shifting. Even with my automatic I often shift it. I grew up with and for most of my life drove manuals, and just prefer them. I’ve never driven a CVT, but my understanding is that you cannot control the ratios in any manner other than to use the gas pedal.
First, I do not disagree with Chunky. Earlier in this thread, I stated that I know people, myself included, that regularly beat the EPA estimates with a manual but most people, myself included, have trouble achieving the EPA estimates with any type of automatic transmission CVTs included.
I only challenged the notion that CVTs slip all the time. If you define slipage as metal surfaces moving against each other, then both the CVTs and the geared transmission have some slipage.
Now if you define the slipage as the input shaft turning faster than the output shaft by more than the ratio of the two, then geared transmissions have no slipage. If a CVT is slipping based on that criteria, then it has a problem.
As to matching top gears, when I had my Saturn with a manual, depending on conditions, I typically shifted between 1800 and 2200 rpm. At each upshift, the rpms would drop to between 1400 and 1700 rpm. In my Subaru, the CVT holds the engine at between 2000 and 2200 all the time while accelerating. That means, on the hole, the engines average rpm is higher than the Saturns. I would prefer that the transmission was a little quicker to upshift so that my engine speed was a little lower, like around 1800 rpm, but that is not the case. I’m pretty sure the Subaru would get better gas mileage if did. Not as good as the Saturn, but better than it does now.
Is any manufacturer offering CVTs with a means of custom setting the “shift” points (the changes in the ratio based on the sensor inputs, or perhaps the sensitivity of the CVT’s ration changes to the gas pedal)?* If not, perhaps they should!
*I have to admit, this is a rare instance where I’m having trouble articulating my thought. 
Keith: " CVT holds the engine at between 2000 and 2200 all the time while accelerating"
It’s been my experience that the RPM depends on the throttle position. Gentle pressure results in lower RPM. (Forester CVT). I can keep it at 1.5k for example.
However, when I had a manual transmission, I used 3000 for my shift point. I kept the RPMs between 2k and 3k.
Mine has paddle shifters, but it wont let you shift unless the arrows in the dash tell you its OK. Even though I still drive a manual in my truck and shifting is so automatic to me that I always shift at what I consider optimum, I can’t seem to master those paddle shifters. I only use the down shift paddle in a situation like a sudden down hill curve.
When you do use the paddle shifters, you are selecting a range and not a specific gear ratio. If the transmission don’t like your choice, it overrides you.
paddle shifters with a CVT? strange. The whole idea of a CVT is to not shift at all.
Yup, paddle shifters with a CVT. Fortunately the downshift paddle works in the automatic mode, you don’t have to move the shifter to manual first.