How is NuVinci Hub differs from Sturmey Archer (IGH) system?

[Biker Chick]

How is NuVinci Hub differs from Sturmey Archer (IGH) system? I am thinking of changing my rear derailleur to Internal hub system. Hate the uneven shifting .. Gear skipping. Sorry for hijacking the thread

 

[spinningmagnets]

The NuVinci uses steel friction balls rubbing against steel rings, and the pivots of the balls change their angle. This means it has no "steps" when shifting. Within its range, it can be adjusted to provide any ratio. A 7-speed Nexus has several small steps to make it easier to find the best possible gear for any given hill, a 3-speed IGH has a big 30% jump in between each of the 3 gears. The NuVinci can make incredibly tiny changes in the gear ratio.

Another benefit is that the NuVinci can be shifted at a stop. With many IGH's, you have to train yourself to down shift while the bike is still moving, just before the stop. If you come to a sudden unexpected stop, you will be starting in a high gear, and you have to get the bike moving before you can downshift.

For a mid drive, the NuVinci cannot take high power, but I have heard they work well with a 750W BBS02

Here's a video: https://www.youtube.com/watch?v=kN8CCY1vFC8

 

[scfoster]

Another benefit is that the NuVinci can be shifted at a stop. With many IGH's, you have to train yourself to down shift while the bike is still moving, just before the stop. If you come to a sudden unexpected stop, you will be starting in a high gear, and you have to get the bike moving before you can downshift.

For a mid drive, the NuVinci cannot take high power, but I have heard they work well with a 750W BBS02

Here's a video: https://www.youtube.com/watch?v=kN8CCY1vFC8

Which is specifically why I have one on order for my BBS02 powered bike. Lots of sudden stops for red lights and traffic in urban commuting, so I find it difficult to downshift quick enough and set up for the start. This results in painful gear grinding and awkward start in traffic which I would rather avoid.

 

[John in CR]

Other than the continuously variable gearing, the biggest difference is the low efficiency of the NuVinci. At it's most efficient, which I believe is at the direct 1:1 gearing, the NuVinci is only 90% efficient. I recall that getting that minimum 10% loss out of the manufacturer was like pulling teeth, and they never did give us any efficiency info throughout the range. That's obviously because it must be even higher at lower gearing. Those using them on pedal bikes report the drag feeling similar to riding around on tires low on air. With an electric it's quite likely that it's possible to gain much of the efficiency loss back by using the NuVinci to allow your motor to spin up to higher rpm where efficiency is higher, the extra weight of a NuVinci and it's relatively low torque handling make it dubious as an electric drive system component. You would come out way ahead in terms of efficiency and durability by investing that weight in more motor.

As far as IGH's, some have tried them with electric drives, and from what I've seen none have held up to more than low power use. If you run such a low power motor that variable gearing is required, then give up regen and the ability to roll backward and go with a Retro-Direct 2 speed.

 

[pjgold]

There is no doubt that the Nuvinci is less efficient in direct comparison.

The interesting question is how much efficiency is gained by being in the correct gear with the motor spinning a peak performance and not loosing power as heat?

I have just changed from an Alfine 8 IGH to a Nuvinci 360 with a BBS02 750w but I haven't done enough kilometers on it yet for a good assessment.
http://endless-sphere.com/forums/viewtopic.php?f=6&t=65590

 

[Chalo]

If you can't be bothered to keep derailleur gears in adjustment, do yourself a favor and avoid internally geared hubs like Sturmey-Archer and SRAM. If you let those go out of adjustment and ignore the warning signs, you can break them expensively. They are low-maintenance, but they aren't for people who can't be bothered to fix stuff when it needs fixing.

However, the NuVinci is unique in that it's always "in gear", which is to say fully engaged and capable of transmitting its maximum rated torque. You'll never hurt a NuVinci by running it out of adjustment because it doesn't really have any adjustments that matter to the hub. The adjusters only affect shifter feel.

The spectacularly expensive Rohloff Speedhub has a similar quality; not of always being in gear, but in being more or less immune to misadjustment at the shifter and cables. It's the most efficient gearhub of all, with the widest range of ratios too.

 

[Chalo]

Another benefit is that the NuVinci can be shifted at a stop. With many IGH's, you have to train yourself to down shift while the bike is still moving, just before the stop. If you come to a sudden unexpected stop, you will be starting in a high gear, and you have to get the bike moving before you can downshift.

For a mid drive, the NuVinci cannot take high power, but I have heard they work well with a 750W BBS02

I've never run across a gearhub that can't be shifted at a dead stop. Most of them won't shift when there is a significant effort at the pedals, though; they wait until the torque eases and then complete the shift.

The original NuVinci N171was rated for 5kW of mechanical power, and the newer N360 is rated for half that much if I remember correctly.

 

[melodious]

Putting 900ish watts into a nexus 7 via 36v 25a middie in a 20" wheel. I'm currently at 400ish miles and it's still functional, meaning my inane habit of trying to flog the motor & IGH into an IGH scrapfest has so far been unsuccessful. Part of my success is really due to the ramping of the motor, relieving undue stress to the drivetrain.

 

[d8veh]

I used a Nuvinci N360 on my GNG crank-drive. It makes riding the bike a bit more complicated, especially if your controller is based on speed control rather than current control. If you can't get in the right gear with a derailleur, I don't think a Nuvinci will solve your problem. Instead, you should look for a 500w geared motor like a MAC, BPM or Bafang CST. You don't have to worry about gears with them. If you're caught in a too high gear, you just open the throttle until you get to a high enough speed for pedalling. They're much more relaxing for commuting and touring.
As mentioned, the Nuvinci starts to slip at about 1000w from the battery too. Also, it doesn't like to shift under the higher torques you get from crank-drives.

In summary, they're good if you have a front hub-motor or a low-powered crank-drive.

 

[amberwolf]

Remember the NV input is not so much "power"-limited, as "torque"-limited.

As long as you don't exceed the torque limits at it's input (meaning, you gear the input to it based not on the speed you want out of it, but rather the max torque your system is able to put into it), it'll probably survive fine up to the actual power limitation of whichever version you get.

Alternately, you can limit the max torque output of the system prior to NV input by limiting the current to the motor (via controller settings), based on the motor's torque output vs current, and your gearing ratios needed for the speeds you're after, etc. THat method means you aren't limiting your *speed* via gear ratios, just limiting torque input to the hub to below the NV's limits.




FWIW, one other difference between the NV and the SA (and other IGHs, probably not including Rohloff) is that at least some of those IGHs suffer from "lash"-induced stresses, when the gears are not fully meshed and then high motor torque is suddenly applied, slamming the teeth against each other. This appears to be the cause of a failure mode seen in some disassembly pics of failed units (like in one of AussieJester's build threads, I think it was), where teeth are broken off at the root, and then they can rattle around in the IGH where it is possible for them to get in between other teeth and cause further damage.

It's more a matter of IGH design, and manufacturing precision, than of how an IGH actually works, but since the NV is always in contact and doesn't use teeth, it doens't have "lash" like that. It has *other* potential issues with sudden hard application of torque (like slippage), but those shoudl only happen if it's outside ti's torque and/or power limits.

 

[kriskros]

i use a Nuvinci 360 on my wood bike with a 42 v,20amp lipop and a 1600 wat cyclone mid drive .. hill climbing often draws as much as 45amps.. neverhad a problem.... 47kph with a 20" rear wheel :|