The Nuvinci CVP Hub Transmission - It's So Smooth!!!
This is currently a rough draft version. Information and opinions expressed here are subject to change. We will be adding pictures and more information soon.
Internal transmissions for bicycles have been around for years, and while advances have been made, the Nuvinci CVP is a totally different type of hub. A typical internal hub transmission uses a set of gears or combinations of gears to achieve different speeds or gear ratios. Because each gear ratio requires its own set of gears there is a practical limit as to how many gears you can put in a cycle wheel hub. Each of these ratios are spaced apart to provide a total gear range. The Nuvinci CVP hub transmission does not use gears internally, but instead uses ball bearings to change the ratio. The Nuvinci hub is called a continuously variable planetary transmission referred to by both the acronyms CVP and CVT. Continuously variable means that there are no distinct steps between the different gear ratios. The gear ratio can be adjusted infinitely within its total gear range. This works because the Nuvinci hub uses an input and output plate that the planetary bearings rotate around. As these plates move the effective rolling diameter of the bearing is changed, resulting in a different gear ratio. To really understand what's going on internally I recommend watching their video.
The beauty of the Nuvinci transmission is that you don't have to understand it to use it and appreciate it. The reasons to go with any type of internal hub transmission are numerous. For me the primary reasons are:
Easier Shifting - The actual twisting of the shifter is typically easier with an internal transmission than with a derailleur. This is mainly due to the mechanism sliding instead of the chain having to move to another sprocket.
Shift at any time - Internal hubs can be shifted while coasting or even stopped which absolutely cannot be done with a derailleur system.
Reliable - Since all the gearing elements on an internal hub are protected by the hub's housing they are protected from the elements. While an internal hub still has an external chain, it will ride up higher since it does not need to run through a derailleur. This means the chain is less likely to pick up dirt.
Less Maintenance - Cleaning the hub usually involves just spraying it down.
The Nuvinci CVP has all of these features. Since there are no gears in the CVP hub it is less likely that an internal component would break versus other internal hubs, even under extremely high torque scenarios. The Nuvinci is essentially a zero-maintenance hub. When it gets dirty just hose it off or scrub it down. There is never any reason to open the hub, as the Nuvinci has a special fluid that does not need to be changed. While gears will build up shavings after a while and require changing the oil, the ball bearings in the Nuvinci hub will not cause the same wear.
One of the nice things about having an internal hub, is that the chain no longer has to move from one sprocket to another to change ratios. To further simplify your drivetrain I recommend using a single chainring or a Schlumpf High Speed Drive up front. The Nuvinci hub, has a maximum torque input rating that allows for a 2:1 chainring/rear sprocket ratio. This means that if you are using a 19-tooth sprocket on the Nuvinci hub, your front chainring should be 38-tooth or larger. By changing your chainring in front, or the freewheel sprocket in the rear, the effective gear range can be moved up or down. Here are some examples using a 19T sprocket with a variety of chainrings on our trikes:
With a 19T sprocket on the Nuvinci Hub, the 46T chainring will provide a good range for most riders, but if you are a strong rider or want to go faster you may want a larger chainring or smaller sprocket. If you have lots of hills then you may want to go with a smaller chainring up front and/or a larger sprocket in the rear. Combining the Nuvinci with the Schlumpf HSD will give you a very wide range of gears great for going up and down hills. The Nuvinci can use freewheel sprockets as low as 16-tooth.
Installing the Nuvinci
The easiest way to get the Nuvinci hub on your trike is to order it with your trike, or bring it in for us to install. If you will be retrofitting your own trike with the Nuvinci CVP hub here are a few tips. The Nuvinci shifter uses two cables to push and pull the shifting pulley on the hub. So, you will need to run new cables. We suggest routing cable housing all the way from the shifter to the hub instead of using a split cable configuration like the stock rear derailleur uses.
Because the hub's shifter housing can be rotated, it is very easy to line the axle's locknuts with the trikes dropouts. Once the wheel is in place choose the angle for the shifter housing and press it on. Threading the shifter's spindle is the most difficult part of installing the Nuvinci hub. Follow the included insructions and have some patience.
Since you no longer need the rear derailleur, it can be removed from the trike. You will need some way to adjust the tension on the chain. If you will be keeping multiple chainrings on the front of your trike you need to make sure that there is enough chain in the system so each chainring can be used. If you choose to do that, you need to use a chain tensioner that can take up an adequate amount of chain. A problem arises here though because most chain tensioners mount to the rear derailleurs position. The Nuvinci's shifter housing prevents any of the standard derailleurs we have found from fitting. You'll have to be creative. Fallbrook Technologies (maker of the Nuvinci CVP) has told me that they will soon have a custom chain tensioner.
Running the Nuvinci CVP with a single chainring (or a Schlumpf HSD) makes things much easier. Just wrap the chain around the rear sprocket and the chainring and cut it as short as possible without going too tight. You can use a half link if you are inbetween links, or you can simply slide the boom forward some to tension the chain. On our aluminum trikes you can do the final tensioning by sliding the front boom. Our steel trikes have fixed-length booms, but the booms can still be slid forward by as much as an inch. If you do want to use a tensioner, the most promising tensioners we have found are the YESS versions that are thinner and can mount on the derailleur hanger with little modification. Their bottom bracket tensioner can fit on the front of the trike and doesn't need to be modified.
Nuvinci on the Road
Riding with the Nuvinci is a different riding experience than what you're used to. The Nuvinci CVP has a 350% gear range and takes a full 360-degree twist of the shifter to go from one end to the other. Because you have such a wide range of motion you can really fine tune the gear ratio you want. Going from one extreme to another will require more than one twist to go all the way around. I find that I need about three twists to make the shifter go the full 360 degrees. The shifter indicator is clever and visually shows what range you are in. When you are in an easier gear ratio the shifter shows a hill (as if you were climbing a hill). When you twist it to a higher ratio the indicator shows a straight line. This would be very evident on a horizontal bar, but with the vertical position of the majority of our trikes, it takes a little getting used to. Basically, don't worry about the indicator. Just twist it one way or the other until it feels right.
As you ride, you'll find yourself reaching your ideal cadence and then fine tuning your gear ratio. This is almost exactly opposite of a standard gearing setup, where you shift first and then adjust your cadence range to the gear. Twisting the shifter is addictive, and I find myself almost constantly adjusting the gear ratio. It is such a different riding sensation that it is hard to explain. It is kind of like having your own personal controllable torque converter. There are no clicks as you slide from one ratio to another. There are no slight jerks in the drivetrain as the chain jumps in the derailleur. It is just smooth, so smooth.
Like most internal hub transmissions you can change gear ratios while stopped or coasting. The Nuvinci CVP shifter can also be used while you are riding. Drastic shifting while riding (vs slight fine-tuning movements) feels a little weird though and takes some getting used to.
The more force that you apply to the pedals the harder it is to shift. This is particularly the case if you are shifting from a high ratio to a lower one (down shifting). The first time I experienced this I thought something was broken, but I just let the pressure off the pedals and the shifter turns very easily.
Really, about the only negative comment I have about the Nuvinci CVP is it's weight. It adds about 7-9 lbs of weight over the stock wheel, cassette, and derailleurs. All of the weight is in the rear wheel, so it does feel like it takes a little more effort to get the wheel spinning. Once you are out riding though, the weight is not very noticeable. If you are a weight weenie, or are looking to race, the weight will undoubtedly be a big issue. If you're looking for a great commuter hub, the 350% gear range and easy shifting makes this a great solution.
We often hear questions about the Nuvinci's efficiency. While the manufacturer won't come right out and provide efficiency numbers they do say: "we believe that the overall 'ride' efficiency of a NuVinci CVP is potentially better than that of internally geared hubs and may in some circumstances exceed that of derailleurs." Because it is such a different riding experience, I found it somewhat difficult to directly compare the Nuvinci with other internal hubs. The efficiency of always being in the right gear is definitely an advantage of the Nuvinci hub.
In our test we took three trikes with different drivetrains. One trike with the Nuvinci CVP, another with the Shimano Nexus 8 Premium hub, and another with the SRAM X.9 derailleur. We put the X.9 setup in its middle gear and then marked the distance traveled with one pedal revolution (gear inches). We then matched that by trial and error on the Nuvinci. We took turns riding each trike around in this single gear position. Once we completed that we put the Nexus-equipped trike in 4th gear and matched it with the Nuvinci trike. After riding all three setups we felt we could make a pretty good comparison. We all felt that the standard derailleur setup had the least drag and was the easiest to get moving. The Nuvinci setup felt like the hardest to get going mainly because of the weight (considering that we were in a middle gear). Once moving all three gearing setups felt about the same. Considering the wider range of the Nuvinci hub (350%) versus the Nexus 8 (300%) at only a slightly higher cost, I'd say that it is a pretty good option.
One thing I haven't mentioned yet is how quiet this hub is. If you are familiar with other internal hubs you know that they usually have a "gear" sound. The Nuvinci hub is practically silent. One thing that they've done is include an extremely quiet freewheel. While most freewheels will produce that familiar "tick-tick-tick" ratchet sound while coasting, not so much with this one. Making the freewheel quieter adds some drag I'm sure, but as long as your pedaling it won't matter.
Changing a flat tire
Another issue to consider when dealing with internal hubs is how easy it will be to change a tire when you get a flat. Of all the hubs that I've dealt with, the Nuvinci is one of the most difficult to remove. For this reason I'd recommend pairing it with a tire like the Schwalbe Marathon Plus, or putting a liner in your tire. If you do need to take of the wheel, you'll need to first remove the shifter housing at the hub.
Overall, I am really glad to see the Nuvinci come to the market. It is a terrific first generation release and I have no doubt that it will develop a devoted following. I love that you can dial in the gear ratio. This is perfect for a rider like me that likes to stay at a consistent cadence. I'd like to see them come up with a shifter mechanism that I could quickly twist from high to low, but I can live with the current set up. Other than that, Nuvinci will completely dominate the market if they can drastically lower the weight.