CVT Nuvinci/ worthless for hill climbing

Discussion in 'Transmission / Drivetrain' started by jawnn, Feb 13, 2010.

  1. jawnn

    jawnn Member

    The Nuvinci gear-hubs for bicycles are worse than useless, they can't handle more than 26 gear-inches of torque with human legs meaning that any motor will make them slip. :shout:

    The maximum torque before it starts slipping is 130Nm or 96 LbFT . One wheel revolution to one crank revolution is the lowest gear possible.

    Some one told me they saw a video of some guy jumping on the pedals, and thought that it showed how strong the thing is. All it really shows is that it takes much more leverage to move in higher gear. And it shows how strong the chain is; I have torn chain links just climbing hills in low gear.

    However there is an application that my be useful; let the motor do the job of bringing the bike up to a speed that you can pedal in high gear. the motor will have to be connected to the other side of the wheel.

    Has any one experienced this device differently?

  2. jawnn

    jawnn Member

    Am I wrong?

    gosh I was hoping that some one would prove me wrong by now.

    I realy like the idea of this device...:jester:

    If any one can climb a steep hill with one fo these please tell the estimated total weight and the grade of the hill and the speed.
    Last edited: Feb 20, 2010
  3. give me vtec

    give me vtec Active Member

    I have ridden my red barron in shell beach.... it almost idled up a hill I could not have pedaled up on a regular bike with a fixed gear to save my life. I would have definitely had to walk the bike up the hill. TOM knows what I am talking about... I am sure he has ridden his bike there.

    I have to respectfully disagree... maybe it was your clutch???? The way the nuvincci hub is designed... there is no metal to metal contact, nothing to slip... the torque transfers through a fluid. There is NO WAY for the nuvinci hub to slip.... NO WAY, NOT POSSIBLE
    Last edited: Feb 20, 2010
  4. SirJakesus

    SirJakesus Guest

    I've climbed long steep dirt roads and trails with mine that are literally a workout just to walk up hauling a pedal bike, which I've done several times. Just enough throttle to engage the clutch is all it took to haul my 200lb arse, the bike and the NuVinci kit. I don't know where you got your information from but I think these hubs would explode before they slipped. Theres absolutely no give in them. As far as them being impossible to pedal, it all depends on the sprockets you're using to drive the hub. Generally mine feels like it gears down to the pedal cadence of first gear on a 21 speed. A virtual crawl when pedaling.
  5. Pablo

    Pablo Motored Bikes Sponsor

    While I have NEVER rode a Shifter Kit bike with a NuVinci - YET - we have sold quite a few Shifter Kits to people with NuVinci's. In fact the some of the first kits two years ago were sold to a fellow with NuVinci's. Not one person has ever reported slipping.
    MotorBicycleRacing likes this.
  6. jawnn

    jawnn Member

    is this hub usable on steep hills?

    I have been trying to understand how to use a Nuvinci hub to climb steep hills. But I just can’t get past the idea that I may neede too much torque for the hub. And what if anything will happen to the hub if over torqued.

    The Nuvinci forum is usless for information.

    5mph with 400 to 500 lbs on an 18% grade powerede by a reasonable size motor,up to 750 watts, 36 to 48 volts.

    We use 20” drive wheels and don’t care to go faster than 20mph. we can not use V belts because of the extreme humidity here. Timeing belts work but not on an expanding pully.

    Is it possible to reduce the torque for the hub simply by reducing the seed before the hub?

    What is the maximum grade we can expect to climb with the hub?

    We need photos of a bike or trike set up correctly.

    It seems very difficult to get info about these things......what WOULD happen if over torqued?
    Last edited: Feb 22, 2010
  7. professor

    professor Active Member

    I don't have one either, but it would slip given sufficient tq. How could it not?
    They give you a torque rating, meaning- go over that and it slips. The reason it doesn't slip even for a big rider is the reverse gear ratio going from the crank back to the hub - your foot lbs. of twist gets cut down by the final drive ratio.
    I would also be surprised if anyone- even strong guys can put down,say 200 lbs/ft. of tq, since the pedal crank is a lot shorter than a foot and some body wt. is not being used.

    In the case of the off road use, you still stay under the rating because the miniscule torque generated by the engine(even multiplied by a gear ratio) is again, under the tq. rating.
    As was mentioned the principle is very similar to the old Paxton blowers only, there is a very different viscous fluid internally. Cleaver engineering.
  8. loquin

    loquin Active Member

    professor: Per their site, it "uses rolling traction to transfer torque." Ref the drawing from fallbrook's site, below. Depending upon the unit, three to twelve metal balls, mounted on an axis which can shift angles, placed between a pair of discs. There IS a lightweight oil inside, but, it's not used to transfer the torque.
    edit by loquin: My bad. The special oil is used in a thin-film state, and under pressure it does act to increase the transfer torque from rolling ball to disc surface. Apparently, a thin film, under pressure, requires a high shear force before it breaks down. In the words of the manufacturer, it acts like 'liquid gears.'

    jawnn: Suppose you weigh 200 pounds, you're on a standard bike, with a 38 tooth chainring and an 18 tooth freewheel. And you stand up on the front pedal. Your weight of 200 pounds is supported on first one pedal, the the other. Since the length of the crank is about 6 inches, the torque at the crank is therefore 200 * 6 inches / 12 inches per foot, or 100 foot-pounds.

    Now, the chainring is 38 teeth, and the rear sprocket is 18 teeth. So, the torque at the input of the Nuvinci becomes 100 * 18/38, or 47 foot-pounds.

    Since the hub is rated for 96 Ft-Lbs, you're good. On the above bike, the rider's weight would have to be more than 408 pounds before he would see any slippage when standing on a pedal...

    Attached Files:

    Last edited: Mar 10, 2010
  9. professor

    professor Active Member

    I do recall something (might have been in the Nuvinci video) about a special fluid they use that is key to it working - I just went to the Utube vid (can't figure out how to link) named" NuVinvi bicycle CV "and they explain about the fluid in the model demo.
    I suppose whatever drag is in the system is caused by the fluid.
  10. machiasmort

    machiasmort Active Member

    O.K., It's obvious somebody here had to use one of these things!

    How are they mating the engine drive sprocket to the hub? Is it for use w/shift kit (right side drive) only?
  11. ibdennyak

    ibdennyak Guest

    Well, I have one, but haven't finished the bike it is on yet. It is a bit heavy, but I am also eliminating the weight of the derailleur and associated mechanics. I may be getting ahead of myself, but I am pretty confident from reading reports, and going over the specs that it will do fine for me. IMO of course. Mine will be driven by a dual freewheel on the right side for the for pedal, and one for engine, with virtually no drag gong from one to the other. hopefully. :grin5:
  12. jawnn

    jawnn Member

    Motor torque?

    So far no one is saying any thing about what a motor will do to it.

    Will a one HP or even a 750 watt motor over torque it? well maybe if set up correctly it can accelerate slowly? but at what gearing?

    And will I ever be able to climb the any hills with 450lbs?????

    I presume that over torque will make it SQUEAL?
  13. professor

    professor Active Member

    The hub's intended application is for a bicycle, not likely a quarter ton bike. And not likely a quarter ton hill -climb bike.
    You are out in the wild frontier where no man has gone.
    Also, any motor that is in it, will likely over heat unless it geared real low to relieve the load placed on it or it water cooled and designed for such a load -regardless of the type of motor and drivetrain.

    Everything has limits.

    I peronally don't like to test limits unless I am protected from possible catastrophic results. It's also not enough to feel lucky.
    Sorry that we cannot answer your questions.
    Last edited: Feb 24, 2010
  14. loquin

    loquin Active Member

    jawnn - do you have this hub installed? Because the title of your thread implies that you do, and it has been proven to be useless for hill climbing.

    The info I saw, said that the hub was rated up to about 6 HP

    1 HP is 746 watts... (750 when rounded to the nearest 10 watts)

    The formula for calculating torque when you know the HP is

    T = (HP x 5252) / RPM

    If we assume that you've geared the motor down to about 120 RPM, then, for a 1 HP /750 watt motor, the torque is 43.8 ft-pounds.
    Last edited: Feb 24, 2010
  15. loquin

    loquin Active Member

    Also, note that few roads in this country have greater than 10% grade. (a 10% grade is a pretty steep road...) For a 10% slope, you would need, for a 450 pound load (inc. bike, motor and rider,) apx. 45 pounds 'thrust' to maintain speed.

    With a 24 inch wheel (chosen because the radius of a 24 inch wheel is 1 foot...) then the 1HP motor geared down to 120 RPM would almost take you up the hill unaided. At 117 RPM, it would do so.

    117 RPM on a 24 inch wheel is 8.35 MPH

    If you're using a smaller wheel, the same RPM would, of course, produce a speed that is less, by the ratio of wheel diameters, and the slope attainable would be correspondingly greater (again, by the same ratio).
    Last edited: Feb 24, 2010
  16. jawnn

    jawnn Member

    The hills here are too steep.....

    I was in the practice of clibing a 16% grade with 400 lbs with just my legs using oly 10.5 grar inches, not quit low enough. My psoas muscle is killing me now so I must stop and pay for power.

    the hill is short but messures a 3.4" ? rise over 20"... it's been a while sence I messured it. maybe it changed.....not.

    well I found this thread good info.

  17. Pablo

    Pablo Motored Bikes Sponsor

    I thought I did.

    You need to contact Clotho. He is not a small guy, he lives in an area with hills and has had a shift kit and Nuvinci for almost two years.

    You use the word "worthless". No way.
  18. Pablo

    Pablo Motored Bikes Sponsor

  19. loquin

    loquin Active Member

    "120 lbs pull (55kg).will lug over 400 lbs up a 25% grade!"

    This is a de-rated calculation; the maximum 'thrust' output calc for the Nuvinci was 170 pounds...
  20. jawnn

    jawnn Member

    what I realy need

    There is a lot of effort to say that the thing will not slip if set up correctly.
    If a one hp motor is several times stronger than I am I would have to put a 76 sprocket chain ring on the motor and 18 on the hub, that may reduce the torque but increase the speed witch will not be reduced any where enough to actual drive a heavy load up a steep hill.

    I use 10 gear inches 18 sprockets on the crank and 34 on the hub with a 20" wheel to climb a 16-17% grade [(4"/100) / (24"/100)= .16666] at 1.5 mph with my legs only.

    Obviously I really need a motorcycle transmission and connect the to the drive wheel with an automotive timing belt. Last year I tore two chain link plates, not at once, but I am using the bicycle stuff at its limit. A motor would destroy it much faster.
    Last edited by a moderator: Dec 15, 2015