Gear Ratio with Predator 212cc and jackshaft

Discussion in 'Hubs, Gearboxes, Sprockets and Chains' started by Predator303, Oct 16, 2012.

  1. Predator303

    Predator303 New Member

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    Not quite sure where to post this but maybe someone with experience with this engine can give me a tip before I order the sprockets.

    I bought the engine from somebody in this forum and he ran the following setup

    13t clutch
    22t JS in
    9t SJ out
    48t rear sprocket

    I get a ratio of 9.026

    [​IMG]

    He said he had around 50mph at 6700rpm

    Now my goal is a good cruising speed of 50mph at a lower rpm

    The website where I can order the jackshaft only offers the JS sprockets from sizes 10 to 18 and it would be great to order everything from one place.

    So if I order the clutch with 12t then 18t in, 10t out and to a rear sprocket of 44t (which i still have around here somewhere)

    I get a ratio of 6.600

    [​IMG]

    If I calculate right, this would mean I can go same speed (50mph) with about 4904rpm. Which sounds perfect but then again I think it might be a little too long the ratio because of the start from dead stop.

    Now from what I heard the engine got lots and lots of torque so here is the question:

    Do you think this is a too long ratio for launching from dead stop?

    Compared to my current bike with a slightly tuned (higher compression) 80cc running a 34t sprocket in the rear I can still perfectly launch from dead stop without paddling so im pretty sure with a monster like the Predator it should be no problem with this ratio setup. Or not? ;)

    The clutch I want to get engages at 2.000rpm
     
    #1 Predator303, Oct 16, 2012
    Last edited: Oct 16, 2012
  2. dmb

    dmb New Member

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    carefull if thats the one i think it is. it can spin the hub clamp right through the spokes. looks like you got your wish. very good deal. now buy a big shoehorn. dennis
     
  3. Predator303

    Predator303 New Member

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    Can somebody explain me the different options they sell here and why you would either recommend a jackshaft or torque converter? And also - what rear sprockets are being used in the case of the converter??

    [​IMG]
     
  4. Predator303

    Predator303 New Member

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    Nevermind. I ordered everything :)
     
  5. potbunny

    potbunny New Member

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    what did u order and where from? is your engine stock, or is the governor removed? i am also making a bike and want a good speed, did yours turn out ok?
     
  6. JonnyR

    JonnyR New Member

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    take a look at his build thread most of your answers are here and its a sweet bike

    he got it already race ready from another member and saved a boat load on it

    governor is long gone look for buck0s videos he posted in the thread i linked

    what kind of speed do you want is the key to all of this this is a bicycle still
    http://motorbicycling.com/showthread.php?t=43358&highlight=predator
     
  7. potbunny

    potbunny New Member

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    i dont think i want to remove the governor as ive been told that it reaches 5500 rpm max with it...i was looking at 50 or so its on a chopper with pretty thick tires. i am completly ignorant to gear ratios, clutches, rear sprockets and all of that jazz, i honestly have no idea what im doing at this point. i really just want to run a chain from a 12 tooth clutch that engages at 2800 to a 55 rear sprocket and see what i get...do you think that will work? what are your suggestions?
     
  8. JonnyR

    JonnyR New Member

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    all governors are set to 3600

    and you need a 10:1 reduction from the motor since its a chopper you dont need the offset like the rest of us do but it may need to go the other way so you may still need a jack shaft
    to work right it would be a 120T rear sprocket a 55t if you could make the power to pull that gear is something like 80-90 MPH the gear reduction is the other reason we use a jack shaft so we can use a 40-55T rear sprocket its taken up at the jack shaft
     
  9. potbunny

    potbunny New Member

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    so i need a jackshaft? what sizes do i need on the jack shaft and rear sprocket? the same as predator did above? i would hate to take out the governor and i dont want to unless i really have too. what size sprockets should i use to get maximum speed?
     
  10. JonnyR

    JonnyR New Member

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    it idels at 2200 if your clutch in gauges at 2800 and the govenor is at 3600 that gives you 800RPM to use

    the sprockets arnt hard to work out its division mostly if your clutch is 12T and your rear is 55T thats 4.58:1
    with the suggested AGK jack shaft ratio 12T clutch 22T in 9T out and a 56T rear is 12.44:1
    if you switch to a 44T rear or a 11T on the output of the jackshaft it brings it close to 10:1
     
  11. potbunny

    potbunny New Member

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    and how fast do i go? and what if i get a 1800 to 2000 clutch i found
     
  12. JonnyR

    JonnyR New Member

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    your clutch wont work then the engine idles at 2200

    top speed is determined by rim size and max RPM
     
  13. potbunny

    potbunny New Member

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    and what is my top speed? is that the fastest i can possibly make it go to start out from a dead stop? i found a clutch that engages at 1800 to 2000, would taht help?
     
  14. JonnyR

    JonnyR New Member

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    no because it engauges below idle so you cant start the engine without it engauging top speed with the governor is not going to be to high 30ish without it 50 ish
     
  15. potbunny

    potbunny New Member

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    so what is ur final desision i should use to get the highest speed...and what would that speed be.
     
  16. JonnyR

    JonnyR New Member

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  17. potbunny

    potbunny New Member

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    so i need a 12t clutch 22t in 11t out 44t rear and that will amke me go 50 mph? how do u calculate top speed?
     
  18. potbunny

    potbunny New Member

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    i just found a gear ratio calculato and to get 10.083 i need a 10t out and a 55t on the axel
     
  19. JonnyR

    JonnyR New Member

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    thats about the highest geat ratio it should pull stock with the governor you will never see 50MPH without it you should be able to do it but the rest of the bike is going to need extensive modification wheels bearings tires forks the stronest frame you can find its not a cheap build alot of the guys have $1500-2000 in there 212cc bikes
     
  20. potbunny

    potbunny New Member

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    ok how fast can i go with the set up we have just established with the governor?
     

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