Yes. We've got one or two.
No, it doesn't help you go faster than the young turks with giant legs who ride derailleur bikes.
Here's what it does do...
We have some second-generation NuVinci internal CVT hubs on our bikes, and they ... are... GREAT!
Can't say enough good things about 'em.
NuVinci is the name of the hub.
We will save you the explanations of what goes on inside their hub, except to summarize like this:
The hub is totally enclosed and sealed against the weather.
Shifting takes place inside where they use spheres (balls) instead of toothed gears to vary the drive ratios, and a special fluid that momentarily turns into a solid, to transmit power.
The axel has ONE gear cog on the outside (unlike derailleur systems that have five, seven, nine... gears), and no spindly shifting mechanism or moving metal parts to catch on things or to rust.
OK, there's still a chain and that one cog, but the chain stays on that one cog all the time. It doesn't jump around.
The shifting is done by a special twist shifter on your handlebar, that has no clicking or indexing. Instead, it has a little rider icon on a tiny line to represent the road. When you shift to what would be "low gear", the "road" bulges up so the little rider appears to be on a hill. When you shift to longer and longer "gears", the "hill" flattens out until the rider is cruising the flats, just as you would be doing.
But... and this is the key part of it all... there ... are... no... gears.
Yup. It's all one continuous, smooth change in the ratio of input to output. It works the same as gears, allowing you a low range to a high range, much like a derailleur cassette, but with none of the switching and clicking and clanking. Did we say smooth? Smooth. And quiet.
When you arrive at a stoplight, on a derailleur bike, you must pre-plan and downshift before your wheels and pedals stop moving. Otherwise, you remember too late and you do that dance where you lift the back wheel off the ground and attempt to kick the pedals around while you attempt to downshift, all in aid of starting off in low gear when the light goes green.
When you arrive at a stoplight, on a NuVinci-equipped bike, you shift any time. The hub just shifts when you tell it to, moving or not. Even if you start off in high gear, having forgotten to shift down, you just twist the shifter and the shift happens while you are pulling away from the stop line. That is just so cool.
While you are riding, the terrain changes, the wind-speed and direction change, and you just unconsciously twist the shifter until it feels right.
There are no 'gears', so it's all smoothly continuous. You move it to where it feels right for the current speed and cadence, and it's there.
There is no "transmission hunting" where the gear you are in is just a bit too tall for the slope you are on, but the next ring is just a little too short... because... there are no gears.
There are no "forbidden" gear combinations. That's what happens on an external-gear (derailleur) bike when you have your chain on (say) the biggest ring of the chain-ring and the smallest ring on the back wheel. That's too big an angle for the chain and it can slip, strip gear teeth, and do other nasty things. Nope. You can have one, two, or three chain-rings on your crankset, but you'll have just the single gear on the back wheel, so with the NuVinci there's never an extreme-angle problem with the chain positioning.
Another problem that happens with multi-gear cassettes on the back and multi-ring cranksets on the front is that there's often a lot of overlap. That is you can have two or three different front-to-back gear combinations that work out to essentially the same gear ratio (so all but one combo is wasted). That doesn't happen with the internal hub NuVinci.
Yet another problem of multi-gear bikes is gaps in the gearing. That's one of the major reasons why they cram so many gears on front and back - so there won't be any big stretches in the gear range that aren't covered by a front-and-back combination. But see the previous paragraph... the more you add rings and cogs to ensure no gaps, the more you introduce useless duplication, and the more you complicate the whole system.
The more complicated a system - the more mechanical bits it needs, to work - the more things can break.
For example, when you have nine gears out back and three rings on the front, you might have a click-index shifter designed to skip over the duplicate and "forbidden" gear combinations. Well, it's nice that they can do that, but it's yet another thing on your bike to go wrong.
The NuVinci shifter doesn't have any clicking or fancy mechanicals inside. It's got two cables. You twist one way and one cable gets pulled, and in turn pulls the shifting ring on the hub in one direction, which also takes up the slack on the other cable. Twist the shifter the other way, and the second cable pulls the shifting ring in the opposite direction. Hard to get simpler or more reliable than that. Oh, and the little-guy "icon" that shows the shift position? That's basically a rubber band that gets pushed and pulled when the grip-shift is twisted. No fancy mechanicals there, either.
We mentioned that the hub is sealed at the factory? No maintenance. It laughs at dirt and road-salt - we've already had 'em through one winter in Canada, with no problem. We cleaned the chain and exposed single gear (and the chain-ring) a few times during the winter, and we made sure that any movable bits had lotsa lube, and that was the extent of our maintenance. Come the summer, we hosed-off, wiped down, and everything was in perfect shape.
[UDATE 2013: We're currently in the middle of our second winter, and it's workin' fine. ]
A derailleur would scream and run for cover.
We mentioned, elsewhere on this site, that we're all about doing what it takes and no more? "Minimum effective dose"? Well, the low (no) maintenance NuVinci bicycle hub is a fine exemplar of that philosophy.
Recommended. You or your LBS (local bike shop) will have to build it into a new wheel, but that's no big deal for experienced bike mechanics.Here's how to get to their site Fallbrook Technologies For the NuVinci Continuously Variable Planetary Transmission. Worth a look for your next bike, or as a retrofit on your current bike.
If this page wasn't where you wanted to be, then click here to return to the homepage from this CVT page.
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