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Is the NuVinci N360 like having a Biopace chainwheel?
#1
I wrote this a while ago and posted it on the old forum but forget about it until now. It’s something I thought of and might be of interest.

Anyone who frequently switches between a derailleur and a NuVinci equipped bike may have noticed that there a something different about a NuVinci bike, apart from having no gears. The way the pedals respond when you push against them, there isn’t that feeling of a direct connection you get with derailleur gears.

Having read the topic “Inner gear ratios of the NuVinci 360” it made me think, could this be explained by something that was written about in this topic?
What is the effect when the bicycle is being ridden of having the ratio to some extent dependant on how much torque is transferred through the hub?

It is written in all the N360 specifications that the ratio range is 0.5 underdrive to 1.8 overdrive. However it has been discovered that with an extremely low torque the range is higher at 0.56 - 0.58 underdrive to 2.0 – 2.1 overdrive.
This means that in the “dead spot” of your pedal stroke the ratio will be higher, which is the same effect the Biopace type of elliptical chainwheel was designed to create.
The original elliptical chainwheels are the opposite and have a lower ratio to get you through the “dead spot” quicker.

There have been a lot of debates in the past about the benefits of non-round chainwheels and which type is best. As far as I can tell due to the way the NuVinci hubs work you end up with the equivalent of an elliptical chainwheel whether you like them or not.

According to my calculations the change in ratio between the power part of the pedal stroke and “dead spot” is approximately equivalent of a 42t chainring becoming a 48t.It depends on a lot of factors but it gives a rough idea that what I’m talking about is not insignificant.

As the ratio change is driven by torque could this be like a perfect biopace chainring?

An advantage of biopace chainrings is better traction. I’m convinced that NuVinci hubs have the same characteristic. I have slick tyres on my bike and I’m always amazed at how much traction I have when off-road. The lower the ratio and the harder you crank the pedals the more elliptical the chainwheel that the hub mimics and the more it smooth’s out the power to the wheel.
- Oran
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#2
I did not notice that on my own bike... Of course I am geared for road though.
The only thing I realise is when I am shifting while pedaling, it take a lot of movement to feel a difference in my legs.
It may have something to do with the torque... Since the torque I apply on the pedals doesn't change much, the ratio stays in the same spot even if I "shift" ???

One thing is sure, this hub has been smooth on my knees from the beginning!
I think I will be opening it sometime soon just to check how it looks inside with a little wear.
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#3
The delayed shifting may be to do with your electronic shifter. The more torque the hub is transferring the harder it is to shift. Although it’s possible to shift under load the hub will tend to resist and instead shift when the load is reduced such as between pedal strokes.

If you could take a look inside your hub it would be interesting to see if there is a difference in the wear pattern. You should have done enough mileage to see some wear, if you give the hub as much abuse as I do.
- Oran
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#4
The electronic shifter has more torque than my hands can give!

As for wear, my hub must have around 2 500km, maybe more... I lost count!

I was thinking about draining the fluid, filtering it to remove metalic particles and re-pour it in.
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#5
That sounds like a good idea. You’ll have to drain the fluid anyway if you want to examine the wear because the stator has to come out of the hub.

I’m having more issues with leaking seals on the pre 2012 hub I’m still using. This time it’s the 40 x 47 x 4 seal around the freewheel. I’ve come to the conclusion that it has to be the metal particles that are making the seals fail.
- Oran
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#6
If only Fallbrook could give us a clue about what fluid is used inside those hubs!!!

We, serious riders could "maintain" our hubs and make them last... but I think that their target customers are casual riders on hybrid bicycles...

I think I will be giving the sanotrack lube a try once the warranty on the hub will be over...

I could drill a drain plug hole to so that it does not have to be dismanteled every time!
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#7
I can tell you what traction fluid they use but I’d be amazed if you can find any of Valvoline's INVARITORC 638 for sale.

It would be fun to try some sanotrack lube and see if my calculations are correct. I would predict that the hub will slip. For sanotrack lube to work the clamping force needs to be more than 10 times that of torque, preferably 12 – 14 times. A NuVinci hub provides a clamping force of only 8 times according to my calculations.

A drain plug hole is a good idea for dismantling the hub as well. As you will find out it’s difficult to drain the fluid when the hub is built in to a wheel.
- Oran
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#8
Might worth a look... Valvoline is not offering this oil only to Falbrooks...

http://www.nuvinci.com/valvoline_THreadable.pdf
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