NuVinci? Holy grail of motored bikes??

[duivendyk]

It is certainly possible in principle to use a smaller (lower torque engine) and make up for it with more reduction (lower speed) in order to negotiate steep hills.But then your speed on the flats will be reduced since you would otherwise be overrevving the engine.Look upon it as hill-assist.What I am saying in effect is that a gearbox, a CVT or a multispeed hub becomes the more indispensable,the smaller the engine is !.With a larger engine you would not have to gear down so much to make it up the hills and would have a higher max. speed.The ultimate along this line is a large displacement engine that loafs along on the flats,but still has enough torque to make it up (most) hills.Engine torque is basically proportional to displacement, a 70cc engine will have about twice the max. torque of a 35 cc one.Most frame mounted ones are in the 50/70 cc category.If reliable engines were around and the cops would not get on your case, this has a lot going for it.There is considerable doubt that the Chinese engines commonly used pass muster.Cheap thrills for people who love to tinker,but reliable transportation for commuters?,I have my doubts about that.
Various solutions to the gearing problem have been proposed or implemented,a recent radical one dispensed with pedaling ability alltogether,used the crank as a jack shaft to drive a multispeed hub or a rear derailler.The engine has to be pull-start.This has obvious legal ramifications.If an extra drive sprocket could be mounted on a geared hub,the pedaling function could be retained.Staton Inc managed to do this feat with the NV hub,but axial room is lacking on the others,which is too bad,because it would prob. be cheaper than the NV hub.
Some intrepid mechanical genius has managed to incorporate a 2 speed derailer on a left side output Staton gearbox and make it work,commendable, but regrettably not for sale as far as I know. Say an extra 1.5 ratio reduction,in conjunction with a torquey 50 cc engine would in my opinion go a long way towards mitigating the hill/flatts problem.

 

[loquin]

The ultimate might be to pair a Comet CVT with a GEBE (although that snap-on ring seems a kludge to me.) You would have an approximate 3:1 reduction at takeoff & hill-climb situations, ranging to a .85 to 1 increase in RPM under low-torque cruising situations. An overdrive, if you will. It's not as much of a range as the Nuvinci, but, a less moolah, and an easy to service system.

The comet, with a new belt, is around 95% efficient. The efficiency drops gradually as the belt wears, so, regular maintenence would probably include replacing the CVT belt every X thousand miles... Coupled with an apx. 95% efficiency rating from the GEBE belt drive, you're looking at an 85+% total system efficiency with new CVT belts, and 80% with worn belts. That I could live with.

 

[duivendyk]

That looks pretty good to me, transmission wise,a 3.5 range is really an overkill,the NV was intended for use in regular bicycles,3:1 is adequate I think,suppose you go down to 10 mph at 6k rpm in "low" gear, you could still cruise at 25mph at 5k in overdrive,which is not bad at all. I haven't a clue how it works out mechanically though.

 

[SirJakesus]

I have the nuvinci and it's it makes a MB a whole new beast. In the very high and low ranges under high torque you do have to let off the gas to shift but other than that all the shifting is smooth. If you stay light on the gas during acceleration you don't have to "clutch" at all and you can keep your engine humming along at the same rpm while still accelerating. It is a bit heavy but not overly so especially since its very low on the bike so I don't think it really affects handling or the feel of your bike. It's best feature other than its incredibly wide range of gear ratios is the fact that it's basically maintenance free. All you have to do is keep it clean and it keeps on doing it's thing. I have climbed some pretty serious DIRT hills with this thing and a mitsu tle43 with NO pedaling. It does give you better gas mileage since you can overdrive and keep the engine at fairly low revs and low throttle while maintaining the same speed. In my neck of the woods the roads are very rough, especially the dirt ones, and extremely hilly. I'm constantly shifting to keep the best engine rpm and speed. After 450 miles on my staton nv kit it hasn't missed a beat. Even if there were cheaper solutions out there why would you choose a system that needs more maintenance and needs parts to be replaced? From what I read the internals of the hub create very little friction as a special type of fluid is used that temporarily turns into a solid when compressed while the drive spheres move along. Staton included the dealer service manual in my kit for the hub and all it basically deals with is cable maintenance and adjustment and installation. Theres no mention in it of internal parts that need adjustment or periodic replacement but we'll see. I'm guessing it's going to outlive the engine.

 

[duivendyk]

I quite agree, having one myself,the NV is expensive and teamed up with a Staton box, on the heavy side,but if you live in hilly surroundings there are no good alternatives. For moderate terrain( below 5%hills),there might be cheaper alternatives,that's why I was looking at the internal gear hubs.For many applications a Shimano 4 speed hub with a 1.84 range would be adequate.I think you can get dual sprockets on the thing (with some machining),but you would lack freewheel capability on the pedal input and would therefore be subjected to forced exercise,not everybody's cup of tea I would imagine.

 

[edrock]

I've been on the lookout for a Black Nuvinci hub, with disc brake mounts for around $400(shipped).

I ran across this, this morning.
http://www.abikestore.com/Merchant2...eetwood-cruiser&Category_Code=&Store_Code=cbs

I cant wait to get it, next week. I feel kinda bad that I'm just buying it for the rear wheel/hub. Looks like I'm going to need another spare bike parts bin.

 

[machiasmort]

sidenote: as crudely mounted, as our "Happytimes" sprockets are mounted to our spokes. I have only had one broken spoke in 4 years.(with 4 bikes)
Spokes are really pretty tough.[/QUOTE]

You are a bigger built guy, too aren't ya? That's not bad if you consider the stress on those tiny little spokes. It's all about fitting the rag washer in there.