Just a thought Nuvinchi hubs

Clotho

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The Nuvinci has a pretty wide range already. If you should ever feel the need for more you could always use a dual sprocket freewheel like this one at the bottom of the page. DOS Freewheel you wouldn't even need a deraileur.
 
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jasonh

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While we're talking about the NuVinci, I noticed they will be selling a "developers kit" for light electric vehicles for $600. Has the regular hub, plus an electronic shift controller - which means an "auto" trans and wouldn't get the authorities so uppity. Thought it would be a cool idea for a bike...

Fallbrook Technologies
 

Dan

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Awesome idea Goat Herder! With a reducing jack shaft, 2 chains (like some electrics) and freewheeling cranks,would be an internal shift. Just woke thinking about your idea. Could easily be done and would work great. Would need a chain guard (round, flat plastic sheet) between the largest rear bike sprocket to isolate the engine chain but would work.

This could be a winner!
 
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Dan

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with an electric 30% would be an incredible loss. With gearing on a ICE would it be as great a concern? And not worth the return...

Asking
 

happyvalley

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Since my motor of choice is 1.6HP I would be losing a third.....down to about one horse.
Fairly significant.

This is presuming, of course, the Ebike guy on that link has it right at 30% loss.
Comprehensive dyno test would be the only true evaluative measure, but that's why I asked.

Aside from the cost, which comparatively speaking is more than something like the Nexus but far less than the Rohloff, there is the weight factor.
For me, this is a real trade off on the NuVinci coming in at around 9 lbs.
 

happyvalley

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Yes, I have seen the Fallbrook tech literature but considering it comes from their internal engineering dept. I would hardly expect anything different.
That's why I asked about either anecdotal or better yet empirical evidence. The Ebike
site I linked is one of the few conversations on this I've encountered.
On another motored bike forum, a well informed user when asked about the NV confirmed a fairly substantial power loss, in his estimate 25%. He seemed content to live with that however,
explaining his setup is primarily useful in low end torque in the off road riding he does and he
is running a fairly powerful motor.
 

jasonh

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There is always going to be a power loss in any type of gearing/transmission. You would measure this by strapping the motor to a dyno and get an hp reading. Then strap the bike with transmission to a dyno and get another hp reading. Then you can see the power lost. This is why cars are generally rated with hp of the motor, not at the wheels.

But 25% seems way too high.

So yes, there will be some power loss, but it ends up being a net gain in usability since you can go further faster for longer.
 

NEAT TIMES

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THE OLDER 4 WHEEL ATV, THE BANSCHEE WAS FAST. THEY USED CHAIN DRIVE TO AVOID SHAFT DRIVE (GEARS) POWER LOSS. I DO NOT KNOW HOW THIS WOULD RELATE TO NU VINCI..flg.
 

Clotho

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Anytime you make a system more complicated and add more parts (ie. a transmission) to it you will likely increase friction as well. This increase in friction correlates to a decrease in efficiency.

I found this quote far down the page Here

Internal gear hubs have a efficiency of 92% compared to 98% for derailleurs. These numbers are valid for new and perfect trimmed drivetrains!

Internally geared hubs like the Shimano 3, 5, 7 speed hubs are cleaner and simpler to operate so why doesn't everyone use them? 2 reasons. They are heavier and they less efficient than a derailleur style transmission. The difference may only be 6 percent between them but for many cyclists that would be 6 percent too much.

Our application is different however and other features such as gear range and durability are also important. I have found the Nuvinci to be excellent in both categories.

The Shimano style internally geared hubs may be 92% efficient but the Nuvinci is probably even less based upon the design. If you try to find hard numbers from Fallbrook they seem to evade the question and instead tell you to ride it and see for yourself. They claim that the ease of shifting and the ability to always be in the right gear overcomes any increased loss in efficiency. They may be correct.

As an example I have 2 bikes that are very similar. Both have 70cc (true) motors with the same hp modifications right down to the same style expansion pipe. Both have street tires and are well maintained. The biggest difference between them is that one has a Nuvinci hub and the other has a conventional derailleur. The Nuvinci bike has more top end and accelerates better. Now I know this doesn't make sense because of my statement that I thought the Nuvinci is less efficient. I get that impression from when I pedal them without being under power. The derailleur bike seems to take slightly less effort. So why is the Nuvinci bike faster? Perhaps Fallbrook is right and being able to always be in the right gear and smooth shifting counteracts any loss in efficiency. It is hard to tell but one thing I am certain about. If you are going to put a gas motor on a bike the decreased efficiency of the Nuvinci hub is more than made up for by all its other qualities.
 

happyvalley

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As an example I have 2 bikes that are very similar. Both have 70cc (true) motors with the same hp modifications right down to the same style expansion pipe. Both have street tires and are well maintained. The biggest difference between them is that one has a Nuvinci hub and the other has a conventional derailleur. The Nuvinci bike has more top end and accelerates better.
Good stuff. It's great to see some actual side-by-side experience cited as empirical evidence.

How are you transferring power from the engine to the rear wheel on the two bikes, left side drive sprockets or a jackshaft to the drive train?

Reading through the comments on the hub blog you linked I thought this was interesting also:

July 25, 2008 at 12:09 pm
Switching from derailleur to shimano nexus -8 has reduced my average speed on a 14 mile commute by 6%. This indicates an efficiency reduction of over 15%, considerably more than you state above. We are getting definitive efficiency measurements done for greenpower electric car racing & I will try to post results here. Results from that forum suggest that the Nuvinci CVT is significantly less efficient still. Note that the shimano alfine now has roller bearings on its planet gears and their advertising proudly boasts “our most efficient hub yet”. With those bearings & OEM grease replaced by automatic transmission fluid, this hub might get up to rohloff standards for efficiency, which would be a profound improvement!
 

jasonh

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Would it not stand to reason then that the higher top speed you mentioned with
the NuVinci is simply because of the higher overall gear ratio of the internal hub over
the traditional cog set?
I think it's more of having the "right" gear with the NuVinci. 6th and 7th gear on a derailer bike are pretty much unusable with most of these motors - there's simply not enough power to keep going faster. Now if you have a nuvinci, you can get a slightly different ratio and eek out that little extra speed that there is still power for.
 

Clotho

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I think Jason has it right. both transmissions have room on the top end but being infinitely variable the Nuvinci allows you to fine tune the sweet spot.
 

ChopperDave

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all I know is I love my NuVinci...clocked 52 mph (by gps and 50 by the following car's speedo) on the flats in both directions and there was still more gear than the engine could pull.