Need help with gearing and setup

Discussion in 'General Questions' started by migueralliart, Oct 20, 2014.

  1. migueralliart

    migueralliart New Member

    Hi all,

    I'm trying to get some prebuild questions answered. I'm building a gt2-a frame with a 66cc engine and would like to avoid the sbp shift kit. The problem is I do live in a hilly area and part of my commute is also flats.

    My approach will be to get a rear nuvinci hub and use a disc sprocket adapter and run it straight from the engine to take advantage of the gearing.

    If say my rear sprocket is 20t and the engine one is 10t what would be my range of speeds? I wanna try and keep the engine below 5000rpm for longevity.

    Thanks in advance for any help!

  2. piecepatrol99

    piecepatrol99 Member

    Running the 10Tooth sprocket in the motor to a 20Tooth on the back wheel direct drive will give you a 2:1 gear ratio. Most motors barely have the torque to pull that on flat ground with out a combination of upgrades to the carb, motor and exhaust.
    The gear ratio I've heard recommended most often for direct drive is between 5:1 to 9:1. 5:1 should move you along at about 25 to 30mph, but it doesn't offer a great deal of hill climbing ability. 9:1 is great for hill but you will sacrifice top speed.

    I went with the jackshaft kit into a 7speed internal shift hub. My bike topped out at 32mph pulling my 280lb frame. Hills were not an issue, I just down shifted ;-)
    No pedaling for me except to get the motor started and an occasional red light or stop sign...

    On a side note: sadly the fork on my cruiser broke. I took it back to the store and exchanged it. Unfortunately the cruiser was no longer kept in stock (it was available online only).
    The replacement bike is a flip flop fix. My 7speed hub in a 26" wheel doesn't quite fit the 700c chainstay width. For now I have about the equivalent of fifth gear only.
    I'm so fond of being able to shift I've ordered a 3speed freehub for the 700c wheel and I'm looking into how to make the pedal crank with triple chainrings (one dedicated to the JS output and the other two for high/low range to the back wheel).
    My objective is to make a 6speed bike like few others...
    The really neat trick is going to be mounting an '80s rear deraileur to a horizontal rear dropout while keeping the stock servicing of the rear wheel and not having to fumble with the deraileur when doing service...

    I know you said you're trying to avoid the jackshaft, but now that I'm stuck with a 4:1 overall gear ratio, I don't know how everyone else makes due with direct drive.
    I don't have hills in my area, I've got small and medium mountains...

    IMG_20140722_140842.jpg FB_IMG_1413255836696.jpg
  3. Fabian

    Fabian Well-Known Member

    The Nuvinci hub is well regarded as a hand grenade hub in a motorised bicycle application.

    Just get yourself a SickBikeParts shift kit and be done with messing around, considering the shift kit is well proven to be reliable and bullet proof with the White Industries heavy duty freewheel bearing system.
  4. Fabian

    Fabian Well-Known Member

    If you get a shift kit, you can make this modification to give this level of extra functionality:

    Last edited by a moderator: Dec 15, 2015