Notes on a Nuvinci

[CJ]

Efficiency the downside (for people that want to go far/fast).

It is a mistake to assume that efficiency matters only to people who want to go far or fast. It actually matters MORE to people who want to go easy.

Here's two reasons why:

1) Those who want to go fast are happy to work harder and as you'll see from the graphs, most things are more efficient when you shove like 200W through them, you lose a smaller percentage. Whereas the poor old guy who can't output more than 50W is going to suffer a proportionally much larger reduction in whatever low speed and range he might nevertheless achieve.

2) The faster you go the greater the proportion of your effort goes into overcoming wind resistance and the power to do that increases with the cube of speed. That means to go 1% faster you need 3% more power. On the bright side however, if you are able to ride so hard that aerodymanic (I think I'll leave that spelling mistake as it is!) drag totally dominates your equation of motion: a 3% LOSS of power results in only a 1% reduction in speed! But if on the other hand, you are riding so slow that wind resistance is trivial, so that rolling drag and gravity predominate, a 3% loss of power will take a whole 3% off your already rather slow speed!

Herein lies the problem with how bikes and bike equipment is reviewed: mostly by sporty types. They have enough power and speed to mask the niggling little inefficiencies that loom so much larger for the rest of us.

[Brucey]

efficiency also matters even if you are not pedalling; a local vendor of e-bikes says his customers who have used both NV and Nexus hubbed machines with the same mid-drive motor system routinely get more distance between charges using the nexus hubs. I suspect that the NV might last longer though.

In a carrier bike a NV hub needs relatively little maintenance. I'd advise being sure that the wheel itself is in good shape; loose spokes should be attended to promptly before they have a chance to wear the hub flange.

The owner's manual for the current hub is here

http://www.nuvincicycling.com/_Resources/Persistent/233d7727e2e2eba7ebe2d321fbd8fd78c1450602/Manual%20Nfinity%2020_02_2017.pdf

more here

http://www.nuvincicycling.com/en/service/downloads.html

cheers

[kwijibo]

Thanks for the advice. I'll stop worrying and report back if things change.
The manual suggests the lubrication is good for the life of the hub. Makes me wonder what the life of the hub is,.. only doing city family journeys but they add up amazingly quicky when you are measuring.

[mercalia]

well I wonder whether it is possible to have an automatic version that senses the effort being put into it? now that would be something to try out? no wires no controls just the hub, the ultimate in practicality and simplicity? seamless carefree cycling?

[barrym]

well I wonder whether it is possible to have an automatic version that senses the effort being put into it? now that would be something to try out? no wires no controls just the hub, the ultimate in practicality and simplicity?

Isn't that what the SRAM 2 speed automatic offers. It's speed sensitive rather than effort as such. No idea if there's ever been one with more gears.

[[XAP]Bob]

Efficiency the downside (for people that want to go far/fast).

It is a mistake to assume that efficiency matters only to people who want to go far or fast. It actually matters MORE to people who want to go easy.

Here's two reasons why:

1) Those who want to go fast are happy to work harder and as you'll see from the graphs, most things are more efficient when you shove like 200W through them, you lose a smaller percentage. Whereas the poor old guy who can't output more than 50W is going to suffer a proportionally much larger reduction in whatever low speed and range he might nevertheless achieve.

2) The faster you go the greater the proportion of your effort goes into overcoming wind resistance and the power to do that increases with the cube of speed. That means to go 1% faster you need 3% more power. On the bright side however, if you are able to ride so hard that aerodymanic (I think I'll leave that spelling mistake as it is!) drag totally dominates your equation of motion: a 3% LOSS of power results in only a 1% reduction in speed! But if on the other hand, you are riding so slow that wind resistance is trivial, so that rolling drag and gravity predominate, a 3% loss of power will take a whole 3% off your already rather slow speed!

Herein lies the problem with how bikes and bike equipment is reviewed: mostly by sporty types. They have enough power and speed to mask the niggling little inefficiencies that loom so much larger for the rest of us.

Does it matter more - it certainly has more effect, but if I'm only pushing 50W for 5-10 minutes then losing 10W to something loses about 10W*300-600 seconds = 3-6kJ
If I'm pushing 200W for an hour and lose even 5W (which I think is unlikely, I suspect the loss goes up, just slower than the input) then I lose 5W*3600 seconds, 5 times as much energy loss.

I suspect it impacts both groups in different ways - but you are absolutely right, we need to measure efficiency at the power input, and 'pulsed' correctly for proper comparison.

[Brucey]

Thanks for the advice. I'll stop worrying and report back if things change.
The manual suggests the lubrication is good for the life of the hub. Makes me wonder what the life of the hub is,.. only doing city family journeys but they add up amazingly quicky when you are measuring.

IIRC the original recommendation was that the fluid should be changed after several tens of thousands of miles. I think there is an appreciable chance that it will leak out before then.

cheers

[CJ]

Efficiency the downside (for people that want to go far/fast).

It is a mistake to assume that efficiency matters only to people who want to go far or fast. It actually matters MORE to people who want to go easy.

Does it matter more - it certainly has more effect.

How much something matters is a value judgement and admittedly that makes it open to individual interpretation. But I think that the effect it has on journey time provides the best way of judging how much a thing matters to a person who uses a bike for transport (rather than sport).

It is self-evident from the greater lengths they go to avoid them, that hills matter more to weaker riders. Strong riders on the other hand, do not mind too much that their route includes some long and steep ups and downs. I do not think there are many experienced cyclists who would disagree with the observation that hills do not matter as much to strong rider. And if you do the maths you find that hills have a markedly greater proportional effect upon the journey time of a 50W rider, than one who puts out 200W.

I proved above that mechanical inefficiency likewise has a greater proportional effect upon the speed of a less powerful rider. I thus feel able to assert likewise, that efficiency matters more to riders who are unable, or unwilling, to exert themselves hard, than to those who are both willing and able to give it some welly.

[Roadster]

I'm not sure whether all such weak and feeble riders even realize that some IGHs are less efficient than others, let alone whether it matters to them or not. I mean, if most of them did actually know that, hardly any of them would have bought a NuVinci hub in the first place and the company would have gone out of business long before now.

[Brucey]

the NuVinci outfit is just a small offshoot of a larger company known as Fallbrook technologies (or somesuch) which makes similar drive systems for industrial use. Quite how their business is viewed (is it required to chip in profits to the parent company to support the manufacturing infrastructure?) I don't know.

Regarding efficiency 'does it matter?' then there are various situations that might give a different result. I can think of two disparate ones;

1) If you are riding in a group, then being the strongest or the weakest rider brings its own issues. In most groups being the weakest rider is something only a few would choose, and in most cases the weaker riders would think anything that increased their average speed might be very important. The converse of this is that I have known the strongest riders in a group deliberately hamstring themselves (with more luggage weight or slow tyres) to even things out.

2) For solo-riding utility/touring cycling purposes, one's 'range' may be limited by effort or time available. There is no particular obligation or necessity to ride at any given pace. A less efficient bike just means your 'range' is less than it would be otherwise, or you can carry less shopping home or something.

In the latter instance a rider might choose to sacrifice efficiency for other virtues (like load carrying capacity, ease of use, reliability, or lack of maintenance). Absolute speed is not as important perhaps.

So conceivably the same rider might have a completely different view on the importance of efficiency depending on the occasion, e.g. whether they are riding to work or out on the weekend, riding with a group. I have always had utility bikes , and I would not usually choose to ride these in a group, because they are not always terribly efficient; their place is elsewhere.

However I think it is important that people are able to make a rational choice about what kind of bike they really need, and the choice of transmission is a key part of that. For example if you choose an IGH, you might assume that the reduced burden of maintenance always comes at the expense of speed/efficiency; well it certainly does in some cases, but rather less so in others.

cheers

[Roadster]

Yes of course, but there must be very many buyers of utility bikes for whom the relative efficiency of different IGHs is not just of lesser importance, but is of no consideration at all. I wonder how many of them turn to the salesman and ask, "Under exactly the same conditions, which of these bikes will be the easier to pedal?"; and how many ask instead, "I like the look of this one, but can I change its saddle for a different one three times wider and four times thicker, preferably stuffed with royal jelly?"...

[Oran]

well I wonder whether it is possible to have an automatic version that senses the effort being put into it? now that would be something to try out? no wires no controls just the hub, the ultimate in practicality and simplicity? seamless carefree cycling?

My first post on the forum, couldn't resist joining this conversation as I have a bit of experience with NuVinci hubs. Currently own 6 of them, most I have opened, one was modified, all a bit worn out, most leaked a little but none have let me down yet.

In relpy to mercalia's question, yes it is possible and I'm currently living that dream of mine. If anyone wants to know all about it I post on this forum
http://normandnadon.com/forum/showthrea ... 08#pid5108

And here's an example of some data I recorded. The power meter is also homemade, cost £15, details also on the forum.





Makes for an amazing ride experience and due to years of CVTs I've become so sensitive to my cadence I can estimate my power output by the rpm of my legs. Convinced that optimising cadence based on power is the best way to maximise muscle efficiency but does it make up for losses in the hub that's the question.