GEBE Gearing Questions

Discussion in 'Rack Mounted Engines' started by Dr. J., Mar 21, 2007.

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  1. Dr. J.

    Dr. J. Guest

    How many teeth are on the motor and wheel pulleys? I am trying to figure the gear ratio. Also, does GEBE use a gear reduction where the motor joins the mount or is it a direct (inline) fit?


    Dr. J.

  2. bamabikeguy

    bamabikeguy Active Member

    There are three available, that screw onto the drive shaft.

    Mountain 11 teeth, for acceleration and pull

    Standard 12 teeth

    Highway 13 teeth for top end speed and highest mileage.

    On my demo bike I let folks use I have the standard, and I race along side them with the highway gear.

    I'll make pix you can see close up the grooves in the belt, the grooves in the spoke ring, and the different gears.

    I'll also take a picture of the drive shaft, so you can see how it is attached.
  3. Hugemoth

    Hugemoth Guest

    Dr. J.

    Bamabikeguy didn't address the gear reduction question. There is no gear reduction where the engine joins the mount, it is direct drive (through a centrifical clutch) to the small drive gear/pulley. Also the big ring that snaps on the spokes doesn't have teeth all the way around so it would be difficult to calculate the exact gear ratio.


  4. bamabikeguy

    bamabikeguy Active Member

    Phsew, gotta luv them bachelor of science guys, I was wondering how to explain the gaps in the spoke ring.

    Simple explanation, if you didn't have 3 gaps between the 3 toothed parts, the dam thing would take off when you cranked it.

    The gaps in the spoke rings are basically "idle" position.
  5. Dr. J.

    Dr. J. Guest

    Thanks guys for your replies. If I could find the working diameter of the drive sheave (on the motor) and the driven sheave (on the rear wheel) diameters, the ratio could be found. Would anyone have the measurements handy? I have an ongoing rear engine project and would like to find a place to start concerning gearing.

    Also, can you take off from a dead stop without pedaling using the GEBE setup?

    Dr. J.
  6. bamabikeguy

    bamabikeguy Active Member

    That part is yes, but it is not a big deal to get up to full speed, and peddling maybe 5 times around is enough for the engine to take over.
  7. bamabikeguy

    bamabikeguy Active Member

    Here are those pix, of the gear/belt in various stages.


    Note: the bottom right is Rocinante, my traveling bike.

    Take along a small can of WD-40 or sewing machine oil, a small tad behind the tension arm keeps that road grime from building up, disrupting "free motion".

    The plastic cover hides the grime, but every 500-700 miles take a peek.
  8. turkeyssr

    turkeyssr Guest

    Calculating the gear ratio

    Couldn't the gear ratio calcultion be done via the diameter of the pulley connected to the engine versus the diameter of the spoke ring? :grin:
  9. srdavo

    srdavo Active Member

    Re: Calculating the gear ratio

    yes sirreeeee! :D
  10. mppardee

    mppardee Guest

    24.6:1 gear ratio?

    I was considering the GEBE but wanted to know the gear ratio. I found on their site a passing mention of 148 teeth on the drive ring, and seems to indicate that only 2 out of the 4 quadrants of the drive ring are covered with teeth. So that would be like 148*2=296 teeth total.

    With a 12 tooth gear on the motor, that would be 296:12 or 24.6:1 gear ratio. That would give a theoretical absolute maximum top speed on a 26" wheel of:
    8000 revolutions/minute * 26/24.6 inches/revolution * pi * 60 minutes/hour / 63360 inches/mile = 25.15 mph max speed. If the engine is at 7000 rpms then speed is only 22 MPH.

    The GEBE site quotes top speeds for the 35cc robin-subaru with the 12 tooth at 27-28 MPH - how is this possible without revving the engine to 9000 RPMS?

    As far as I can tell the GEBE does not have any freewheel so if you have the throttle on and you are going down a big hill wouldn't the engine brake you at max RPM and never let you go faster?
  11. Jim H

    Jim H Guest

    Perhaps your calculations are off ? You would probably need to have the items in hand to do a proper calculation; just sayin'...
  12. bamabikeguy

    bamabikeguy Active Member

    Hills are conquered via familiarity and technique.

    When in 7th speed, the momentum has to get around 25 mph for your pedals to catch up to the motor and be able to assist.

    Momentum also gets you up in the lower 40 mph range on the bottom of a steep grade, which is full throttle PLUS. In other words, you want to be full throttle at the bottom of the grade to climb up the other side easier.

    If you were easing along at half throttle on level ground, then going downhill, you could stay half throttle. If you are going full throttle, then decending, might as well stay full.

    There is an adjustment a rider goes through to get acquainted with the engine/clutch potentials, the engine "talks to you", telling you either ease off or give it more throttle on both descents and ascents.

    That is also why you can't let too many strangers ride, they won't know how to communicate with the engine on uphill climbs.
  13. mppardee

    mppardee Guest

    This should be the definitive answer, straight from Julia at GEBE in response to an email I sent:

    By my calculations 22.25:1 gives a top speed of:
    8000 revolutions/minute * 26/22.25 inches/revolution * pi * 60 minutes/hour / 63360 inches/mile = 27.86 mph which is in line with quoted speeds

    Thanks Julia!
  14. JemmaUK

    JemmaUK Guest

    I am getting 34mph on the flat with the #13 gear which seems from tentative calculation to be about right... however I am using the HTD gears..

    Jemma xx
  15. Silvaire

    Silvaire Member

    No one has posted an answer to the original question:
    "How many teeth are on the motor and wheel pulleys?"

    GEBE does not state on their site how many teeth the drive ring has - only the number of teeth of the various pinion options.

    Regarding the drive ring they only make the cryptic statement "...less resistance allows for 148 teeth in the belt track..." but they do not state how many teeth there are on the drive ring.

    Crunching the numbers, there just have to be more than 148 teeth on the drive ring.

    From the information that mppardee posted above, from a response from Julia at GEBE stating:
    "the #12 gear offers ratio of 22.25:1"
    (Despite this number having four significant digits, it can't be all that accurate. This would work out with the drive ring having 265 1/2 teeth, which isn't physically possible.)


    Is there anyone out there who knows this number for certain (or who has a GEBE kit and would be willing to count number of teeth that there are on the drive ring)?

    A BIG "thanks in advance"!



    A thought just occured to me...

    Are there ANY TEETH AT ALL on the drive ring itself???

    If not, can anyone confirm this for me?

    Another "thanks in advance"!
    Last edited: Dec 24, 2008
  16. ocscully

    ocscully Member


    The circumference for the purpose of figureing gear ratios is 267t

  17. seanhan

    seanhan Member

    Don't know how it works but it works great.
    My GEBE Tanaka 32cc does 32MPH on my bike.
    That's 1 MPH per CC
    Ask yourself this. Do you really want to go over 32mph downhill or up hill for that matter?
    The real factor is do you want Chain,belt or friction.. then go from there ...
    I you want to go fast and freewheel down hill the only real option is the STATON chain drive with freewheel, and if you got the bucks get the nuvinchi hub with it..
    You will be a speed demen!!!!
  18. beachcruiser

    beachcruiser Member

    I have a new drive ring sitting by me. They are 74 teeth
    WITH 7/32" SPACING
  19. DetonatorTuning

    DetonatorTuning Active Member

    you are forgetting to consider the # of teeth that could / would occupy the "empty" area.

    the 267T that ocscully gave is correct for working out the ratios using varying drive pulleys.

  20. Silvaire

    Silvaire Member

    Thanks all for your help on this.

    From what I am able to piece together from the three pertinent replies, the GEBE drive ring has some teeth on it, but that it has blank areas between the teeth. Why they would choose make it like this is still a mystery to me though.

    Most important to me is that it has an effective equivalent of 267 teeth. I don't plan on buying a GEBE kit, so at this time I won't try to figure out just why they designed the drive ring as they did. I only wanted to be able to figure their total reduction in consideration for my own design.
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