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NuVinci fixed gear.
#1
The following post is part of a topic copied from the discontinued NuVinci Forum. It contains some posts written by members of the old forum and not by me.

This is for those who have wondered whether this is possible.


by iperov on Sat Mar 10, 2012 7:40 am

How I can remove freewheel and install fixed gear cog ?

Re: Nuvinci fixed gear.
by Oran on Sat Mar 10, 2012 5:49 pm

This is a question that has been asked before. The basic answer is you can probably find a way to do it but it would be a waste of time. CadenceKing’s answer to the same question back in 2008 explains the reason very well so I have quoted it below. It is referring to the N170/ 171 so if you have an N360 the bits about the threaded freewheel adapter aren’t relevant. However the internal workings of the N360 still work in the same way.

As further proof that CadeneceKing is right I have attached some photos of the parts inside the hub responsible for adjusting the clamping pressure. It is obvious that something like this doesn’t work in reverse. The top ring in the first photo is the traction ring which drives the balls. In the second photo it is turned upside down so the ramps can be seen.

[Image: ljm7.jpg]
[Image: 8g8g.jpg]

Citation :One could physically mount a fixed (track) cog onto the threaded freewheel adapter but the combination would not act as one might expect. The hub internals will slip rather than 'drive' in reverse. (You would not be able to backpedal in an attempt to brake.)

(This reverse slippage in the NuVinci hub is not experienced when a freewheel is mounted because it occurs at a somewhat higher torque than the ratcheting action of a typical freewheel - the freewheel 'freewheels' first.)

A fixed-gear NuVinci bike would act like a NuVinci bike with a extremely gummed-up freewheel. As far as handling the "forces in the reverse direction," I doubt this reverse slippage would damage anything. . . I just can't see any reason to do it.

I believe the reason this behavior occurs is because NuVinci has cleverly designed the internal rolling elements so that they are progressively clamped together as the input torque increases. The harder you pedal, the harder the discs and balls are wedged together. . . preventing slippage. When you try to 'back-drive' this system, the rolling elements slip - since they are not being clamped against each other. If NuVinci had taken an alternate (brute force) approach, and simply bolted the hub together with enough clamping force to always prevent slippage at the maximum input torque, the efficiency (and life?) would drop since more losses would occur at the 'rolling' contacts between the discs, tilted balls and within the thrust bearings. Remember, at any ratio other than 1 to 1, the action of the balls on the discs is a combination of rolling (good) and pirouetting (lost energy.) The use of the Valvoline Invaritorc traction fluid further reduces the need for high clamping pressures.

Sorry for the long answer. I'd stick with using a freewheel since the Nuvinci hub does not drive in reverse and my desire is to minimize drag when I'm coasting. By the way, this may be obvious, but the NuVinci hub's freewheel adapter is not threaded for a left-hand threaded lockring (like a track hub is.)

Time to go out for a ride. . .

Regards,

CadenceKing,

........__o
........\<,
......()/()

Re: Nuvinci fixed gear.
by CadenceKing on Sat Mar 10, 2012 8:37 pm

I agree with Oran that the N360 would not be a candidate for a fixed gear system (for the same reason as the N170 and N171 hubs.)

Oran, I enjoyed seeing the photos of the internal parts of the hub! Which model hub is this and how did you end up taking your hub apart? (I've always wanted to study the inside of a NuVinci hub but have feared that it might end up being an expensive misadventure if it turned out that special tools, fixtures and/or gaging were required for proper reassembly! I guess I'll wait until one of mine fails internally.)

Those parts certainly seem to be ruggedly built! Are the roller cage parts molded out of glass-filled plastic? Weight can still be barrier to people considering a NuVinci hub. . . even with the strides made with the N360.

Cheers,

CadenceKing
He's a smooth operator,
smooth operator,
smooth operator,
smooth operator. . .

Re: Nuvinci fixed gear.
by iperov on Sun Mar 11, 2012 12:42 am

its too bad ((
I so want fixed gear and nuvinci

Re: Nuvinci fixed gear.
by CadenceKing on Mon Mar 12, 2012 10:17 am

Hi iperov,

There's no inherent reason which would prevent a continuously variable 'fixed gear' system from working. It's just that the currently available hubs from NuVinci were not designed for that application and, therefore, include the internal wedging system in addition to a freewheel. Bypassing these mechanisms would be way beyond the skill level of the home handyman or garage tinkerer. Unfortunately, "fixies" are a tiny market segment and I can't imagine NuVinci introducing a limited-edition 'fixed' version of their bicycle hub.

As an alternate solution to your problem, have you considered the Sturmey Archer S3X hub. It's a 3-speed, fixed gear hub using a tweaked arrangement of their planetary gear system. Here's a link to more information on this hub:

http://www.sturmey-archer.com/products/h...id/47.html

They were introduced a couple of years ago. The street price for them has fallen. I'm not sure why, but it may be because of saturation of a small niche of a niche market. There are mixed reviews of the hub's performance/reliability online.

Hope this helps!

Cheers,

CadenceKing
He's a smooth operator,
smooth operator,
smooth operator,
smooth operator. . .

I had a think about this while I was editing the post and I think there might be a way of achieving this. My idea is to add some packing beneath the rings so that the rollers are stuck and the bottom of the ramp. In other words the minimum clamping pressure is set a bit higher. This is instead of it being set very low by some springs. The result of this would be that in reverse the hub will be able to transmit some torque.

A potential problem is that if the minimum clamping pressure isn’t high enough the hub will slip in reverse. This idea is only really viable if the torque transferred in reverse is much less than that in forward. Otherwise it’s as CadenceKing said
Citation :If NuVinci had taken an alternate (brute force) approach, and simply bolted the hub together with enough clamping force to always prevent slippage at the maximum input torque, the efficiency (and life?) would drop…
- Oran
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