NuVinci hub on a Grubee 4-stroke Frame Mount

[duivendyk]

The front chain ring has nothing to do per se with the hub itself,wether it has a Nexus or a NV hub.The overall ratio is the product of the front to rear sprocket ratio multiplied by the hub ratio .The Nexus 7 hub has a ratio of 0.632 to 1.545 according to www.sheldonbrown.com .The overall transmission ratio depends on the front to rear sprocket ratio.The NV hub I have came equipped with a 16T rear freewheel, to the best of my recollection.For normal cycling use they require this ratio not to exceed 2 (32 T in my case)The potential problem with the NV hub with a motor drive is that your pedaling speed is proportional to the engine speed,since they are locked together,this can lead to a wide variation in cadence.Therefore I attempted to keep my front deraileur, with limited success since the NV rear freewheel had an unfavorable tooth profile for use with a front deraileur.I had to increase the chain tension a lot to keep it from skipping,making shifting front gears more difficult

 

[Irish John]

The front chain ring has nothing to do per se with the hub itself,wether it has a Nexus or a NV hub.The overall ratio is the product of the front to rear sprocket ratio multiplied by the hub ratio .The Nexus 7 hub has a ratio of 0.632 to 1.545 according to www.sheldonbrown.com .The overall transmission ratio depends on the front to rear sprocket ratio.The NV hub I have came equipped with a 16T rear freewheel, to the best of my recollection.For normal cycling use they require this ratio not to exceed 2 (32 T in my case)The potential problem with the NV hub with a motor drive is that your pedaling speed is proportional to the engine speed,since they are locked together,this can lead to a wide variation in cadence.Therefore I attempted to keep my front deraileur, with limited success since the NV rear freewheel had an unfavorable tooth profile for use with a front deraileur.I had to increase the chain tension a lot to keep it from skipping,making shifting front gears more difficult

The front chainring has a lot to do with pedalling a bike. Given that front derailleurs are not an option with a cruiser bike and 4-strokes go better on cruisers than other bikes, I would have thought you would opt for as big a chainring as possible so you get increased high gears and decreased low gears. That enables you to pedal along at speed which is the object of the exercise. The low gears aren't missed that much because you only need a couple for starting off and maybe cycling the bike if the engine stops running.
In fact derailleurs can be a problem because the chain does come off quite often whereas on hub gears this doesn't happen and the chain tension is constant. What I want to know is why is your pedaling speed proportional to the engine speed - I know that you have whatever CVT you have chosen for the motor to run through the hub but the size of the front chainring means everything because a big one would enable you to pedal slowly at a good speed. It's really important to be able to do this and if the NV can't allow it I can't see why. If I could run the engine chain onto my Nexus 7 it would mean that in top gear I would not have to pedal very quickly to get the pedal chain to be under load. The 44T front chainring on the N7 changes the ratios totally and it works really really well and makes driving the bike realy easy and comfy.

 

[duivendyk]

Of course the front sprocket affects your pedaling rate and deraileurs can have problems with chains,let me explain why the pedaling rate is proportional to engine speed, it's quite simple really,both drives share the input to the hub,it can be driven from either input via freewheels, call that speed S,then the engine speed is S*R (R is the reduction engine to hub), the pedaling speed is S*P ( P is the ratio between rear&frontsprockets),
Therefore the ratio between engine rpm and pedaling speed is R/P 'for instance if R= 25 and P= 1/2, the engine speed will be 50 times the pedaling rate,if your pedaling rate is 80 the engine will be running at 4000 rpm should you want to pedal along with it.This is a fixed ratio set by the gearing

 

[Irish John]

Of course the front sprocket affects your pedaling rate and deraileurs can have problems with chains,let me explain why the pedaling rate is proportional to engine speed, it's quite simple really,both drives share the input to the hub,it can be driven from either input via freewheels, call that speed S,then the engine speed is S*R (R is the reduction engine to hub), the pedaling speed is S*P ( P is the ratio between rear&frontsprockets),
Therefore the ratio between engine rpm and pedaling speed is R/P 'for instance if R= 25 and P= 1/2, the engine speed will be 50 times the pedaling rate,if your pedaling rate is 80 the engine will be running at 4000 rpm should you want to pedal along with it.This is a fixed ratio set by the gearing

Thanks for that Duivendyk. It's late now and I'm going to go to bed and think about that.

 

[sparky]

Of course the front sprocket affects your pedaling rate and deraileurs can have problems with chains,let me explain why the pedaling rate is proportional to engine speed, it's quite simple really,both drives share the input to the hub,it can be driven from either input via freewheels...

Forget all the math, Irish... this is the important part.

You want the largest front sprocket you can get, say 44t or larger if you can find it. BOTH the energy from the pedal chain and the engine chain go THRU the hub. Unlike any other setup, this transmission combines the total input and allows you to change the output ratio. BOTH pedals and engine will shift by twisting ONE shifter, which changes the input/output ratio by moving some ball bearings or something.

The only reason you need a front derailer is for uphill pedaling, but you've already got the hub for that... so you stick with a 44t for greater resistance while traveling at faster speeds. A front derailer with lower gears would only allow you to climb hills better, which would have to be a VERY steep hill since NuVinci seems to be doing alright. If you could find a larger front chainring like 44t + 60t, that might be beneficial to pedaling past 40mph with resistance.

 

[Irish John]

Yes I get all trhat which is why I always have 44T chainrings on my cruisers - anything larger means it can't fit under the chain guard and could impede the engine tray. The 44T with a 7 speed shimano derailleur isn't much good but with the Nexus 7 hub it is great because the gearing ratio is higher and you can pedal at speeds in excess of 45 km\hr. Front derailleurs are great cos the big ring really helps but they don't look good on a cruiser. Hub gears with no derailleur are the answer for 4 strokes I reckon but this NV seems a brilliant idea except I'm yet to read about it's speeds & performance on a frame mounted cruiser. Sir Jakesus gave a good report for his rear mounted Staton NV but I'm yet to read anything very explicit about a frame mounted rig with a NV hub. What I need to know is how it performs on the flat at it's topmost gearing and I can work out the rest for myself.

 

[duivendyk]

I am not all that familiar with frame mount systems,the NV can only be driven from the right side,so both final drives would have to be on that side too.I seem to remember that there is one drive system,for bicycles that is,that had a rear sprocketcluster+ a internally geared hub.This would appear to present at least the potential of having dual inputs on that side.The NV hub is intended for normal bicycles and has an input torque limitation of 95 ft.lbs.Based on that it could handle up to around 3.5/4 Hp,unless you use extremely low gearing.If you want to explore this further visit my thread: "power,torque and rpm,Nuvinci application".Wether it can handle continuous high speeds is an open question,there is a special fluid in the thing,centrifugal effects could impair it's functioning or durability,but there is no evidence for that to my knowledge .Experience will tell I suppose.

 

[Unhappy Time]

I have completed my build of a Cadillac Fleetwood that comes with the Nuvinci hub. I fabricated a jackshaft to bring the power from the Grubee kit to the right side of the hub. I still have some refining to do (play with gear ratio and add front brakes), but the bike and hub work great. Here is a link to some pictures:
http://www.motoredbikes.com/album.php?albumid=275

Wow thats beautiful!

 

[duivendyk]

I am impressed !,I would expect it to handle better than my rack NV setup, which takes some getting used to.Pay attention to the max torque input to the NV.See my thread "power torque rpm,NV application" on that subject